White Paper
Implementing Industrial Ethernet
Field Device Functionality
by Using FPGAs
Executive Summary
Industrial Ethernet protocols like PROFINET or EtherCAT are currently taking over the communication role in automation applications from fieldbuses. These protocols are based on various
Ethernet and IT standards and provide real-time communication capabilities up to and including
isochronous motion control.
The implementation of Industrial Ethernet field devices requires hardware as well as software
components. Different implementation approaches are available. While a conventional implementation for instance uses an Industrial Ethernet ASIC, a modern approach is based on FPGA
technology. Here all the required hardware and software components are combined into just one
component providing maximum implementation flexibility.
This White Paper gives an overview of the implementation aspects of an Industrial Ethernet device
based on FPGA technology and discusses the advantages of using this solution in comparison
to conventional approaches. The aspects of using FPGAs for implementing individual Industrial
Ethernet protocols are presented as well.
White Paper
Table of Contents
1. Introduction.............................................................................................................................. 1
2. Industrial Ethernet Overview.................................................................................................... 2
3. Implementing an Industrial Ethernet Field Device.................................................................... 4
3.1 Conventional Industrial Ethernet Field Device Implementation............................................ 5
3.1.1 Industrial Ethernet Field Device Implementation Based on ASIC.................................... 5
3.1.2 Software-Based Industrial Ethernet Field Device Implementation................................... 7
3.2 Industrial Ethernet Field Device Implementation Based on FPGA Technology..................... 8
3.2.1 FPGA Technology............................................................................................................ 8
3.2.2 Implementing the Industrial Ethernet Subsystem Based on FPGA Technology............... 9
3.2.3 Aspects of Industrial Ethernet Field Device Implementation Using FPGA..................... 11
3.2.3.1 Support of Different Implementation Architectures.................................................... 11
3.2.3.2 Performance Acceleration......................................................................................... 14
3.2.3.3 Hardware Options..................................................................................................... 17
3.2.3.4 Common Application Programming Interface............................................................ 18
3.2.3.5 Required FPGA Resources....................................................................................... 20
3.2.3.6 IT Channel Implementation....................................................................................... 23
3.2.3.7 Evaluation Kit............................................................................................................ 23
4. Implementing Specific Industrial Ethernet Protocols Using FPGA Technology...................... 24
4.1 Implementing a PROFINET Device Using FPGA Technology............................................ 24
4.1.1 PROFINET Technology................................................................................................. 24
4.1.1.1 System Model........................................................................................................... 24
4.1.1.2 Device Model............................................................................................................ 25
4.1.1.3 I/O Data Exchange.................................................................................................... 26
4.1.1.4 Acyclic Data Exchange............................................................................................. 27
4.1.1.5 Device Description.................................................................................................... 27
4.1.2 PROFINET Organization and Specifications................................................................. 29
4.1.3 Implementing a PROFINET Device............................................................................... 30
4.1.3.1 Conventional Implementation of a PROFINET Device.............................................. 30
4.1.3.2 PROFINET Device Implementation Based on FPGA Technology.............................. 30
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4.2 Implementing an EtherCAT Slave Using FPGA Technology............................................... 31
4.2.1 EtherCAT Technology.................................................................................................... 31
4.2.1.1 System Model........................................................................................................... 31
4.2.1.2 Device Model............................................................................................................ 32
4.2.1.3 I/O Data Exchange.................................................................................................... 33
4.2.1.4 Acyclic Data Exchange............................................................................................. 33
4.2.1.5 Device Description.................................................................................................... 34
4.2.2 EtherCAT Organization and Specification...................................................................... 34
5. Advantages of Using FPGA Technology for Industrial Ethernet Field Device
Implementation...................................................................................................................... 36
5.1 Flexibility for Implementing an Industrial Ethernet Field Device......................................... 36
5.2 Further Advantages............................................................................................................ 38
5.3 Support of Different Protocols by One Hardware............................................................... 39
6. Summary............................................................................................................................... 40
7. Abbreviations and Acronyms................................................................................................. 41
8. About Softing......................................................................................................................... 43
9. Authors.................................................................................................................................. 44
10. References............................................................................................................................ 44
11. List of Figures........................................................................................................................ 45
12. List of Tables......................................................................................................................... 46
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1.
Introduction
Following the success of fieldbuses during the last decades, Industrial Ethernet is today, in a next
innovation phase, gaining increasing acceptance with regard to communication within factory and
process automation applications. Industrial Ethernet extends standard Ethernet to suit automation
requirements, and supports deterministic real-time communication with cycle times of 1 ms and
below, which is suitable for all types of applications, including motion control.
Despite all efforts it has not been possible to standardize on just one Industrial Ethernet protocol.
Rather, a number of different Industrial Ethernet variants is available on the market, which differ
from protocol to protocol and which are not compatible. According to the market share the most
important Industrial Ethernet protocols include EtherCAT, EtherNet/IP, Ethernet POWERLINK,
PROFINET and MODBUS TCP.
Basically, it is possible to implement Industrial Ethernet in software only. However, to fulfill individual requirements like real-time behavior with short cycle times and low jitter, support of various
network topologies including daisy chain or ring-based media redundancy, specific hardware
components need to be included in the Industrial Ethernet implementation. Different approaches
are available here. While conventional implementations use special hardware components or
result in a reduced performance, an advanced implementation option is based on Field Programmable Gate Array (FPGA) technology. This approach combines the different elements required for
an Industrial Ethernet implementation into a single electronic component. Application-specific parts
can also be added in a very flexible way.
This White Paper outlines the implementation aspects of an Industrial Ethernet field device based
on FPGA technology and discusses the advantages of using this technology. In the first part, the
focus is on the general aspects common to all the individual protocols. The second part addresses
the protocol-specific aspects of implementing a PROFINET Device or an EtherCAT Slave based
on FPGA technology.
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2.
Industrial Ethernet Overview
Industrial Ethernet is based on the standard Ethernet technology specifying hardware (e.g. cables,
distribution devices, network interfaces) and software (e.g. protocols) components for cable-based
data transmission. However, the requirements of automation communication go beyond these
capabilities and include a collision-free deterministic communication, which is suitable also for very
fast motion applications. Thus cycle times of significantly less than 1 ms combined with minimum
jitter have to be supported. Depending on the achieved cycle time and the jitter Industrial Ethernet
protocols are subdivided into real-time protocols and hard real-time protocols.
These requirements resulted in the definition of the powerful Industrial Ethernet communication technology. It is based on Fast Ethernet (transmission rate of 100 Mbit/s) and makes use of
switches, full-duplex data transmission and message prioritization.
Industrial Ethernet can be understood as the common platform for a variety of individual communication protocols including EtherCAT, EtherNet/IP, Ethernet POWERLINK, PROFINET and Modbus
TCP. In general, it follows the Open Systems Interconnection (OSI) Reference Model (see
Table 1).
OSI Layer
7 - Application Layer
(Software Based)
Standard Industrial Ethernet Implementation
Application Protocol
6 - Presentation Layer
(Software Based)
5 - Session Layer
(Software Based)
4 - Transport Layer
(Software Based)
Transmission Control Protocol (TCP) and
User Datagram Protocol (UDP), respectively
Additional IT Standards
3 - Network Layer
(Software Based)
Internet Protocol (IP)
2 - Data Link Layer
(Hardware Based)
Carrier Sense Multiple Access / Collision Detection (CSMA/CD)1
1 - Physical Layer
(Hardware Based)
Ethernet Transmission Technology
Table 1:
1
OSI Layers and Their Industrial Ethernet Implementation
The access mechanism Carrier Sense Multiple Access / Collision Detection (CSMA/CD) is responsible for
solving data collisions and handles the overlapping data transmission of two or more stations. In contrast,
the use of Switched Ethernet technology avoids data collisions without the CSMA/CD method.
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The OSI layers 1 (Physical Layer) and 2 (Data Link Layer) of Industrial Ethernet protocols are
described by the Ethernet standard. The layer 3 (Network Layer) supports, in particular, the
addressing of stations via IP addresses. Layer 4 (Transport Layer) consists of the TCP and UDP
protocols. IT standards like the Hypertext Transfer Protocol (HTTP) and the File Transfer Protocol
(FTP) are also located at this layer. Layer 7 (Application Layer) provides the application interface.
The OSI layers shown in Table 1 describe the standard implementation parts of Industrial Ethernet
protocols. However, individual protocols make more or less use of this ideal layer model. In fact,
the implementation of these layers varies from one Industrial Ethernet protocol to the next. From
a general point of view the protocols that use more Ethernet and TCP/IP standards provide less
real-time support, while protocols providing hard real-time features are usually based on special
implementations. Here the range reaches from Modbus TCP and EtherNet/IP at the more standards-based and less real-time support end to PROFINET IRT and EtherCAT at the isochronous
hard real-time end with little jitter.
In addition to the differences within the OSI layers, the various Industrial Ethernet protocols also
vary in the basic protocol architecture, the individual application protocol, the object model as well
as the engineering concepts and tools.
When used as a fieldbus, Industrial Ethernet in general makes use of two types of stations,
controllers and devices. Devices typically perform slave functionality and interact with the environment by reading or setting values, or execute motion control applications, whereas controllers
are usually responsible for master functionality such as the calculation of values that are sent to
actuator field devices based on the values read by sensor field devices.
Industrial Ethernet protocols support the “One Ethernet” concept, which defines a joint usage of
the Ethernet cables by the automation application together with IT systems.
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3.
Implementing an Industrial Ethernet Field Device
As the Industrial Ethernet communication is structured in layers (see Table 1), a complete
Industrial Ethernet field device implementation has to address the individual required layers. Thus,
an Industrial Ethernet field device implementation consists of a hardware and a software portion.
The hardware portion of the Industrial Ethernet field device implementation typically comprises
the time-critical functionality, which is responsible for accessing the Industrial Ethernet network at
the logical level. The Industrial Ethernet protocol stack covers the software portion of the Industrial
Ethernet field device implementation, which deals with the remaining communication functionality
(see Figure 1).
Figure 1:
Structure of Industrial Ethernet Field Device Implementation and Its Reference to the
OSI Layer Model
To minimize the dependency on individual suppliers, field device manufacturers in general are
interested in basing an Industrial Ethernet implementation on standard components as much as
possible. In addition, they demand that all the Industrial Ethernet protocols needed are implemented using identical hardware to ensure maximum flexibility.
The following sections present various conventional approaches used for implementing an
Industrial Ethernet field device. These approaches are discussed with respect to the individual
demands of field device manufacturers. In another section a state-of-the-art Industrial Ethernet
field device design based on an FPGA architecture is described.
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3.1 Conventional Industrial Ethernet Field Device Implementation
There are various conventional strategies for implementing an Industrial Ethernet field device.
3.1.1 Industrial Ethernet Field Device Implementation Based on ASIC
The conventional approach for implementing an Industrial Ethernet field device makes use of
a dedicated Application-Specific Integrated Circuit (ASIC). This component combines specific
Industrial Ethernet hardware responsible for real-time access with a processor core executing the
Industrial Ethernet protocol stack.
In general, there are two types of ASICs available for implementing an Industrial Ethernet field
device. One type of ASIC is especially focused on one specific Industrial Ethernet protocol (“Single
Protocol ASIC”). Typically, this type of ASIC is manufactured by the technology leader of this
specific protocol. For implementing further protocols, components from other sources have to be
used, if this is possible at all.
The other type of available ASIC supports the implementation of multiple Industrial Ethernet
protocols with a single hardware platform (“Multiple Protocol ASIC”).
Table 2 gives an overview of advantages and disadvantages related to the implementation of an
Industrial Ethernet field device based on ASICs.
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Relevant for
Aspect
Single
Protocol
ASIC
Multiple Advantage /
Protocol Disadvantage
ASIC
Description
Combined
Component
X
X
Advantage
The ASIC combines the specific
Industrial Ethernet hardware with a
processor core executing the protocol
stack. As a result no additional main
components are required for implementing
the Industrial Ethernet field device functionality, reducing the hardware development effort in comparison to an approach
using standard hardware components.
Compatibility
X
X
Advantage
A Single Protocol ASIC available from the
technology leader ensures the compatibility with other stations within an Industrial Ethernet network. Multiple Protocol
ASICs can also provide this advantage.
Support
of Multiple
Protocols
X
Disadvantage A specific ASIC is required to be implemented for each individual supported
protocol, resulting in additional development effort for each additional protocol.
X
Advantage
Only one ASIC is required for implementing all the required protocols. Thus,
there is no need to support different
hardware platforms.
Closed
System
X
X
Disadvantage The supported functionality is defined by
the ASIC manufacturer. Thus, there are
only limited possibilities of adapting this
functionality to address specific Industrial
Ethernet field device requirements.2
Single
Source
X
X
Disadvantage The Industrial Ethernet field device ASIC
is only available from one manufacturer,
increasing the dependency on the implemented Industrial Ethernet field device.
The manufacturer may discontinue the
ASIC at any time, which directly jeopardizes the availability of an implemented
Industrial Ethernet field device.
Table 2:
Advantages and Disadvantages of Using Single Protocol and Multiple Protocol ASICs
for Implementing an Industrial Ethernet Field Device
2
For instance, there is no possibility to integrate additional hardware-based functionality like motion control
support or to modify the implemented memory interface.
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3.1.2 Software-Based Industrial Ethernet Field Device Implementation
The Industrial Ethernet field device can also be implemented completely in software by making
use of standard hardware, e.g. a PC platform for accessing the Ethernet.
This Industrial Ethernet field device implementation approach involves advantages and disadvantages, which are summarized in Table 3.
Aspect
Advantage /
Disadvantage
Description
Low Price
Advantage
A standard hardware is sold in high quantities and thus is
typically available at very competitive prices, which are lower
than prices resulting from other implementation approaches.
Known
Hardware
and Development Tools
Advantage
The standard hardware plus the respective development tools
are well known. Thus less learning effort is required than for
getting acquainted with an unknown hardware and development
environment, as may be the case with ASICs and FPGAs.
High
Processor
Performance
Required
Disadvantage A purely software based Industrial Ethernet field device implementation requires a high processor performance for supporting
a real-time adequate Ethernet functionality.
No
Guarantee of
Determinism
Disadvantage Depending on the processor performance and the individual
tasks to be performed by the processor, the fully deterministic
responses required for an Industrial Ethernet communication may
not be guaranteed.
Additional
Processor
Required
Disadvantage In order to limit the load of the processor executing the Industrial
Ethernet communication, an additional processor is required to
run the Industrial Ethernet field device application.
Restricted
Disadvantage Not all Industrial Ethernet functionality3 can be implemented in
software on a standard hardware platform. Thus a softwareFunctionality
based Industrial Ethernet implementation typically results in a
restriction of the supported functionality.
Table 3:
Advantages and Disadvantages of Using the Completely Software-Based
Implementation of an Industrial Ethernet Field Device
3
For instance, this applies for support of hard real-time, daisy chain topology and media redundancy.
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3.2 Industrial Ethernet Field Device Implementation Based on FPGA Technology
As the various discussed conventional approaches to implementing an Industrial Ethernet field
device (see Section 3.1) have disadvantages e.g. regarding their flexibility, scalability, performance, usability and/or their cost/performance ratio, it makes sense to look for alternatives when
implementing Industrial Ethernet field devices. When analyzing the market demands, a natural
choice is the use of FPGA technology, which directly results in a number of advantages. Based
on the FPGA-based Industrial Ethernet solution from Softing, this option will be discussed in more
depth in the following sections.
3.2.1 FPGA Technology
The FPGA is an electronic component which can be programmed after its production. FPGAs are
available from various manufacturers, including Altera and Xilinx. The FPGA is structured in logic
elements which, on the one hand, can be used for directly implementing specific functionality and,
on the other hand, also support the loading of individual IP Cores providing pre-engineered functionality. These IP Cores can be “wired together” to provide the overall functionality of an FPGA.
For an FPGA, IP Cores are available from different sources, including FPGA manufacturers and
various service providers. Plus, they also can be developed individually to meet specific needs.
One type of IP Core provided by FPGA manufacturers is the processor IP Core. It allows the
execution of individual programs as in a standard processor. Modern FPGA architectures in
addition include an ARM-based System-on-a-Chip (SoC) hard processor system, providing the
ultimate combination of hardened intellectual property (IP) for performance and power savings with
the flexibility of programmable logic.
Other types of IP Cores support a specific communication technology (e.g. Real-Time Ethernet IP
Core for supporting Industrial Ethernet communication), allow connecting peripheral components
like memory and I/Os, or provide a special functionality (e.g. closed loop control for drives).
A major advantage of this approach is that, based on these individually available IP Cores, a
specific set of hardware and software can be loaded into an FPGA to deliver the desired functionality. As loading into the FPGA is performed at runtime, the support of re-configurability and
updates in the field comes as a free added benefit. All in all, the FPGA offers an additional level of
flexibility unknown in other electronic components.
For implementing an Industrial Ethernet field device, a hardware part (Ethernet real-time access)
as well as a software part (protocol stack) is required (see Chapter 3). Both parts can be ideally
combined into an FPGA, together defining the Industrial Ethernet Subsystem. This combination
is a ready-to-integrate solution and requires only minimal integration effort by the field device
manufacturer. Thus, this White Paper primarily focuses on the internal aspects of an FPGA-based
Industrial Ethernet field device implementation rather than on specific integration tasks.
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Figure 2 shows the overall hardware architecture of an FPGA-based Industrial Ethernet
Subsystem using two IP Cores4.
Figure 2:
Hardware Architecture of Industrial Ethernet Subsystem Implemented on FPGA5
3.2.2 Implementing the Industrial Ethernet Subsystem Based on FPGA Technology
The hardware part of the Industrial Ethernet Subsystem is the Ethernet real-time access. It is
responsible for accessing the Industrial Ethernet network, for transforming the serial data stream
into individual frames, and for observing the Industrial Ethernet timing rules. The Ethernet real-time
access is implemented as an FPGA IP Core and provides functionality comparable to that of a
specific Ethernet hardware component. An overview of the advantages when implementing an
Ethernet real-time access as an FPGA IP Core is given in Table 4.
4
5
In fact the FPGA implementation uses more than two IP Cores, the processor IP Core and the Industrial
Ethernet IP Core being the relevant ones.
The terms used in the figure refer to Altera FPGAs.
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Advantage
No External Parts
Description
In comparison to using standard processors, the Ethernet real-time
access is completely implemented inside the FPGA, together with additional components like memory interface, level shifters, etc. This results
in reduced costs and space requirements.
Possibility to Provide In comparison to using ASICs and standard processors, the FPGA can
Additional
be used for implementing any other application-specific requirements in
Functionality
parallel. Thus, there is no need for additional components. This results in
a highly integrated solution, supporting a small footprint.
Interface Flexibility
Table 4:
An FPGA provides flexibility for accessing external resources. For
instance, the data exchange can be performed via an external dual port
memory or via a Serial Peripheral Interface (SPI).
Advantages of Implementing an Ethernet Real-Time Access Based on FPGA
Technology
In summary, the implementation of a real-time Ethernet access based on FPGA technology uses
an IP Core which supports an extensive set of functionality while focusing on the time-critical part
of the Industrial Ethernet protocol stack. This implementation is 100% compliant with the individual
Industrial Ethernet standard.
The implementation of a real-time Ethernet access is typically available to the manufacturers of
Industrial Ethernet field device applications in an encrypted format which allows them to include
this IP Core in their own FPGA design.
The protocol stack defines the software part of the Industrial Ethernet Subsystem. Industrial
Ethernet protocol stacks are available in binary format for direct execution on a processor IP Core
in an FPGA. As opposed to the classical approach, the stack does not need to be ported to the
target processor and operating system. It is designed from the outset for use with the IP Core and
uses a royalty-free operating system.6 The stack comprises the complete Industrial Ethernet
Application Layer as well as the non-time-critical parts of the Industrial Ethernet protocol.
The use of an FPGA-based Industrial Ethernet field device implementation provides additional
flexibility to the device manufacturer. For instance, it allows supporting a device architecture with
direct access to the protocol stack through an external application. This feature is useful for implementing an application, acting as an Industrial Ethernet controller and device in parallel.
From the user’s point of view, the complete Industrial Ethernet Field Device implementation is
encapsulated and provides an application interface, typically based on a dual port memory, for
exchanging data with an additional application.
6
The Softing approach uses the eCos operating system.
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3.2.3 Aspects of Industrial Ethernet Field Device Implementation Using FPGA
This section discusses some aspects regarding the implementation of Industrial Ethernet protocols
in field devices based on FPGA technology.
3.2.3.1 Support of Different Implementation Architectures
Being flexible and scalable, an FPGA allows different implementation approaches for Industrial
Ethernet field devices, which are all based on an identical communication connection and leverage
the advantages offered by modular FPGA architecture. This makes it possible to select the implementation structure to suit the existing field device resources (such as available microprocessors,
peripherals and memory).
The most flexible implementation approach, which is also suitable for complex field device applications, uses two processors or one processor together with an ARM-based SoC in the FPGA
(see Figure 3). While one processor is responsible for executing the communication protocol, the
second processor runs the device application, such as executing the measurement algorithm,
processing the I/O data or controlling the drives. For this processor, the field device manufacturer is free to choose the environment in which it will run, so that manufacturers can continue to
use existing implementations to a great extent. Alternatively, the integrated ARM-based SoC can
also be used for this task. The two processors exchange information via a dual port RAM and
the application programming interface (API). This implementation approach ensures optimum
load balancing, decouples the communication protocol from the device application, and avoids
mutual interference in resource usage. Additional functionality can be integrated into the FPGA as
required by using additional IP cores, which for example provide access to external peripherals
(General Purpose I/O, GPIO) or contain special algorithms, e.g. for motion control.
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Figure 3:
Allocation of the Industrial Ethernet Communication Protocol and the Device
Application to Two Different Processors Within an FPGA
A second implementation approach places the device application on the same FPGA processor
as the communication protocol (see Figure 4) and is typically used for less complex field devices.
In this case, no dual port memory is required for the exchange of information because the two
components are more tightly coupled than in the first implementation structure.
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Figure 4:
FPGA Processor Shared Between the Industrial Ethernet Communication Protocol and
the Device Application
Another implementation option uses the FPGA only as a communication processor; for the device
application, a separate microprocessor outside the FPGA is used (see Figure 5). This approach
is recommended if comprehensive application software is already being used on an external
processor and there is no need to integrate it into the FPGA.
The communication protocol and the device application can then exchange information in a
number of ways – via dual port memory of different sizes or by using a standard bus system like
Modbus RTU, or standard hardware protocols (e.g. SPI, etc.) with proprietary communication.
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Figure 5:
Use of the FPGA As Communication Processor and Execution of the Device
Application on an External Microprocessor
3.2.3.2 Performance Acceleration
The minimum achievable cycle time of an Industrial Ethernet implementation defines how fast
input and output data can be exchanged between communicating devices. Thus, it is often seen
as an important key performance index of an Industrial Ethernet implementation and used for
comparing different communication systems. As this value is measured at the communication
medium, however, this value does not necessarily allow to determine the supported performance
for accessing input and output data at the application level. Here the delay caused by the implemented mechanism for data transfer between the communication medium and the application has
to be considered as well.
In general, an Industrial Ethernet implementation may also cause latencies related to
• Delays of the PHY component
• Delays of the Ethernet interface (e.g. MAC, switch, etc.)
• Delays of the Industrial Ethernet protocol stack
• Delays caused by the implementation of the interface between the protocol and the application
software
• Delays within the application implementation
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Using an FPGA allows implementing performance optimizations to overcome some of these
various delays.7
When analyzing the different delays of an Industrial Ethernet implementation it can be found that
the major part of the overall delay within a field device is related to the protocol stack. As a consequence, this component offers the biggest optimization potential.
The implementation of a configurable DMA channel for input and output data is a key to significant performance acceleration. This approach uses the DMA channel for the direct data exchange
between sources and sinks of I/O data, bypassing the protocol software. This solution allows to
directly exchange data between the specific Industrial Ethernet IP Core (e.g. switch or EtherCAT
Slave Controller) and the dual port memory or the application’s IP Core. The FPGA architecture
of this implementation is presented in Figure 6. Table 5 shows the delay measured between the
Industrial Ethernet IP Core and the application interface for the PROFINET and EtherCAT protocols.8
7
8
The optimizations related to the Industrial Ethernet implementation are already integrated into the solution
offered by Softing. Additional options for performance improvements regarding the interface between
the protocol software and the application as well as within the application are described in the available
documentation.
The delays shown have been measured based on the Softing FPGA-based Industrial Ethernet
implementation.
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Figure 6:
Performance Acceleration in FPGA-Based Industrial Ethernet Implementations Using
the DMA Channel
PROFINET Implementation
EtherCAT Implementation
Maximum
Delay
Mean Delay
Maximum
Delay
Mean Delay
Without Optimization
160 µs
125 µs
220 µs
150 µs
Using DMA Channel
9.7 µs
9.7 µs
7.1 µs
7.1 µs
Table 5:
Performance Optimization Potential Using the DMA Channel
Analysis of the data shown in Table 5 indicates that the use of a DMA channel decreases the delay
by at least a factor of 15. In addition, it can be seen that the related jitter has vanished completely.
As a result, the implementation of a DMA channel allows to exchange new input and output data in
every cycle at cycle times as low as 50 µs.
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3.2.3.3 Hardware Options
Field device manufacturers can choose from different hardware options for implementing the
Industrial Ethernet field device functionality based on FPGA technology. One is to use an
embedded communication module that comprises all the required hardware and software of the
Industrial Ethernet Subsystem, and is integrated into the target hardware as a piggy-back board
(see Figure 7). Another option is a custom FPGA hardware development, including the Industrial
Ethernet Field Device functionality and all manufacturer-specific functions in a cost-optimized
manner.
Figure 7:
FPGA-Based Communication Interface for Implementing an Industrial Ethernet Field
Device
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3.2.3.4 Common Application Programming Interface9
After defining the FPGA platform as a general hardware platform for implementing Industrial
Ethernet field devices, the next step is to address the requirements of the market and of individual
customers in order to provide a unified interface for programming the application for the various
supported Industrial Ethernet protocols.
Therefore, the individual protocols were analyzed and similarities in accessing these protocols
were identified despite the differences between the individual protocols. These similarities eventually formed the base for the implementation of a common Application Programming Interface (API)
which covers the complete range of supported Industrial Ethernet protocols.10,11 As a result, only
minor implementation modifications during initialization are required within the application when
migrating from one Industrial Ethernet protocol to the next.
The API has been implemented in such a way that it is fully independent of the hardware and
operating system being used. Thus porting is quite easy, resulting in a flexible interface library that
can be used with all types of field device platforms.
Another advantage is that the API can be implemented in very lean way so that just a few protocolindependent calls are necessary to start, perform and stop the Industrial Ethernet communication.
The resulting calling structure of a common API is shown in Figure 8.
9
10
11
From a general point of view the use of a common API is not necessarily related to the FPGA-based
implementation of an Industrial Ethernet field device. Softing has implemented a common API which can
be used for FPGA implementations as well as conventional implementation approaches. This section
describes Softing’s API solution (Simple Device Application Interface, SDAI).
The various Industrial Ethernet protocols differ to some extent e.g. regarding the diagnosis features,
alarming or dynamic I/O data re-configuration. These individual features are implemented in Softing’s
SDAI and require an application modification during the Industrial Ethernet protocol migration, if these are
used.
The idea of defining a common API for accessing various Industrial Ethernet (as well as fieldbus) protocols
has its origin at Softing.
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Figure 8:
Lean Calling Structure of the Common Application Programming Interface for Industrial
Ethernet Field Devices12
12
The shown calling structure refers to the routines implemented in the Softing Simple Device Application
Interface (SDAI).
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3.2.3.5 Required FPGA Resources
The FPGA size required for implementing an Industrial Ethernet field device is driven by the
specific functionality supported in the individual case. Here, it is important to note that the various
Industrial Ethernet protocols do not define and require the same range of functionality: For
instance, some protocols support extended diagnostic capabilities, which, as a consequence,
also require additional resources when implemented. Based on the implemented features the
resources can be determined and the appropriate FPGA size can be chosen. Typical FPGA
resource requirements for implementing various aspects of an Industrial Ethernet field device are
given in Table 7.13
The overall FPGA combining the Industrial Ethernet subsystem plus the application subsystem
is shown in Figure 9. In general, the Industrial Ethernet implementation consists of more than
just the individual Industrial Ethernet protocol stack, but also includes additional IP Cores. The
resource consumption of these additional IP Cores is given in Table 6. Included in these additional
IP Cores is a DDR RAM Soft IP Core. The resources associated with the DDR RAM Soft IP Core
are not required if a Hard IP Core or a memory type other than DDR RAM is used. In addition, the
resource consumption of the application subsystem also depends on the specific use case.
13
The information presented in this section refers to FPGA-based Industrial Ethernet designs created for the
Softing Protocol IP V1.20 using the Altera Quartus 14 design software for an Altera Cyclone V E A7 FPGA
supporting 149,500 logic elements and 6,860 M10K blocks.
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Figure 9:
FPGA Design of the Industrial Ethernet Subsystem Together with the Application
Subsystem
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ALMs Used in Final
Placement
M10K Blocks
866
3
Memory
(DDR RAM Soft IP Core)
2,232
24
Application Subsystem
2,544
25
Functionality
Common
Table 6:
FPGA Resource Consumption of Additional IP Cores Required for an Industrial
Ethernet Implementation
Table 7 shows the resource consumption of the overall Industrial Ethernet FPGA design including
the resources given in Table 6, the resource consumption of the Industrial Ethernet subsystem as
well as the resource consumption of the specific Industrial Ethernet IP Core. Depending on the
implemented Industrial Ethernet protocol the Industrial Ethernet IP Core consists of
• EtherCAT Slave Controller (for EtherCAT)
• Hub (for Ethernet POWERLINK)
• Switch without IRT Support (for PROFINET RT, EtherNet/IP and MODBUS TCP)
• Switch with IRT Support (for PROFINET IRT)
Overall Design
Industrial Ethernet
Subsystem
Industrial Ethernet
IP Core
ALMs
M10K
Blocks
ALMs
M10K
Blocks
ALMs
M10K
Blocks
EtherCAT
18,400
102
13,076
50
7,828
9
EtherNet/IP /
MODBUS TCP
13,358
122
7,409
70
4,732
36
POWERLINK
9,617
125
3,825
73
1,231
40
PROFINET RT
(Cycle Time 1 ms)
13,239
122
7,530
70
4,582
36
PROFINET IRT
(with DMA)
17,156
142
11,198
90
7,283
48
Table 7:
Required FPGA Resources for Overall Design, Industrial Ethernet Subsystem and
Industrial Ethernet IP Core of an Industrial Ethernet Field Device Implementation for
Different Industrial Ethernet Protocols
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3.2.3.6 IT Channel Implementation
Implementing the specific Ethernet hardware based on FPGAs allows to provide individual additional functionality to the device manufacturer. Following the “One Ethernet” concept a separate
internal Ethernet port can be provided, which allows the execution of additional Ethernet services
beyond the scope of the specific Industrial Ethernet protocol, e.g. IT services within the field device
in parallel to the pure Industrial Ethernet communication. This channel can be used, for example,
to update the firmware of the field device or to access a web server which can be used for defining
device parameters.
3.2.3.7 Evaluation Kit
Evaluation kits are helpful for integrating the Industrial Ethernet Subsystem into the field device
as well as for developing the device application running within the FPGA. Typically, appropriate
evaluation kits are available from the FPGA manufacturers.14 These evaluation kits come with a
full-featured development environment focusing on the specific features of the FPGA being used.
14
The Softing solution is available for the Altera INK, Altera CVE as well as the Altera CVSoC evaluation
boards.
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4.
Implementing Specific Industrial Ethernet Protocols Using FPGA Technology
While so far the implementation of an Industrial Ethernet field device based on FPGA technology
has been discussed from a general point of view, this chapter now addresses specific aspects
required for implementing the protocols PROFINET (see Section 4.1) and EtherCAT (see Section
4.2). These aspects include an introduction to the protocol technology as well as a comparison of
conventional vs. FPGA-based implementation approach.
4.1 Implementing a PROFINET Device Using FPGA Technology
4.1.1 PROFINET Technology
PROFINET is an open, cross-vendor Industrial Ethernet communication standard for factory
and process automation. The protocol is based on various Ethernet and IT standards and offers
scalable real-time communication including an optional isochronous mode (PROFINET IRT).
4.1.1.1 System Model
The PROFINET specification distinguishes three different station classes: PROFINET Controller,
PROFINET Device and PROFINET Supervisor. A number of (1…n) PROFINET Controllers
exchanges data cyclically and acyclically with a number of (1…m) PROFINET Devices. A
PROFINET Supervisor can be integrated into the system in addition to the PROFINET Controller.
A PROFINET Supervisor can be used, for example, for commissioning (as part of an engineering
tool) or for the parameterization of PROFINET Devices.
The use of PROFINET requires 100 MBit/s full-duplex, switched Ethernet. The switch functionality
can be implemented as part of an external device (switch) or as part of the automation device. The
use of these two implementation types allows the support of different topologies, including star,
line, tree and ring topologies. A ring topology is a line topology that has been closed to form a ring
in order to support media redundancy. A sample structure of a PROFINET topology is shown in
Figure 10.
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Figure 10: PROFINET Network Structure
4.1.1.2 Device Model
PROFINET Devices are based on a modular device model, in which modules can be plugged into
slots. If a device has only virtual modules and virtual slots that cannot be plugged by the user, this
device is referred to as a Compact Device.
In addition to the modules that establish a connection to inputs and outputs, there is another
special device module type – the Device Access Point (DAP). The DAP is used for modeling the
communication interface of the device. A device family can include more than one DAP. This
allows the description of different interfaces (e.g. copper, fiber optic, 1 Ethernet port, 2 Ethernet
ports, etc.) of the device family.
Slots/modules are further subdivided into subslots/submodules. As no devices supporting
pluggable submodules are available in the market today, this subdivision so far is always a virtual
subdivision. The submodule 0 acts as a special submodule, representing the respective alarm
messages of the module. Thus, the submodule 0 cannot contain any I/O data, records or diagnostic information, while all other submodules provide access to I/O data, records or diagnostic
information.
The structure of the PROFINET Device is shown in Figure 11.
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Figure 11: PROFINET Device Structure
4.1.1.3 I/O Data Exchange
PROFINET supports the exchange of I/O data on a cyclical basis. Different cycles are possible
within a PROFINET system. The transmission cycle of the PROFINET Controller is used as the
calculation basis for the entire scheduling. The transmission cycle is a property of the PROFINET
Controller and describes its performance. Every PROFINET Controller must support a transmission cycle of 1 ms. Other cycles, which may be shorter or longer, can be additionally supported.
The ReductionRatio value is used to define the specific cycles for the exchange of inputs and
outputs. All parameters for the scheduling of I/O data are specified during commissioning and
transmitted to the PROFINET Controller, which distributes these parameters to the PROFINET
Devices at the beginning of the data exchange. The basics for scheduling the cyclic data exchange
within a PROFINET network are shown in Figure 12.
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Figure 12: PROFINET Communication Schedule of I/O Data
4.1.1.4 Acyclic Data Exchange
Within PROFINET networks alarms are exchanged acyclically. They can be transmitted and
acknowledged by PROFINET Controllers as well as by PROFINET Devices.
Read and write access to records is also executed acyclically. A special PROFINET protocol based
on UDP/IP is used for this purpose.
4.1.1.5 Device Description
A Generic Station Description Markup Language (GSDML) file is used for describing the properties of a PROFINET Device. It is based on XML. While GSD is the result of many years of experience with the description of device properties in the PROFIBUS environment, GSDML also
describes extensions that have been introduced with PROFINET (subslots, different communication interfaces, etc.).
XML is used by various PROFIBUS & PROFINET International (PI) workgroups. A style guide has
been created to prevent inconsistencies. The GSDML specification is based on all three sources
as shown by Figure 13.
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Figure 13: Sources of the GSDML Specification
A useful tool for viewing and checking GSDML files is the PROFINET XML Viewer, which
PROFIBUS & PROFINET International (PI) members can download from the PI website. A sample
GSDML file and a representation of the different parts displayed in the PROFINET XML Viewer are
shown in Figure 14.
Figure 14: Different Parts of a GSDML File and Their Representation in the PROFINET XML
Viewer
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4.1.2 PROFINET Organization and Specifications
The different aspects of a PROFINET system (communication protocol, device description,
profiles, installation guidelines, etc.) are defined in different specifications. PROFINET specifications are created by the respective workgroups established by PI. PI members can download the
specifications from the PI website www.profinet.com. PI has about 1,400 members worldwide.
The majority of specifications have been submitted to the applicable international standardization
bodies.
An overview of the currently available PROFINET specifications is shown in Table 8.
PROFINET
Specification
International
Standard
PROFINET IO V2.3
Ed2MU1
IEC61158,
Ed. 4.0
Industrial Communication Networks - Fieldbus Specifications
PROFINET RT/IRT
IEC61784
Industrial Communication Networks - Fieldbus Specifications
Profile Sets – Part 2
GSDML V2.31
ISO15745
Industrial Automation Systems and Integration -Open Systems Application Integration Framework
PROFINET
Security Guideline
V2.0
IEC62443
Security for Industrial Process Measurement and Control.
Network and System Security
PROFIsafe V2.6.1,
PROFIdrive V4.1
PROFINET
Cabling and
Interconnection
Technology V3.1
Table 8:
15
Title
IEC61784-4 Industrial Communication Networks - Fieldbus Specifications
Profile Sets – Part 4
IEC61784-3 Industrial Communication Networks - Fieldbus Specifications
Profile Sets – Part 3
IEC61918
Industrial Communication Networks Installation of Communication Networks in Industrial
Premises
IEC61784-5 Industrial Communication Networks - Fieldbus Specifications
Profile Sets – Part 5
PROFINET Specifications15
(Source: PROFIBUS & PROFINET International)
The PROFINET specification overview reflects the status as per June 2015.
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4.1.3 Implementing a PROFINET Device
4.1.3.1 Conventional Implementation of a PROFINET Device
This section details the discussion from Section 3.1 for the Industrial Ethernet protocol PROFINET.
A PROFINET Device can be implemented by using off-the-shelf microprocessors with or without
integrated Ethernet MAC. This type of device can only support PROFINET RT functionality as
defined by the Conformance Classes A and B.
The implementation of a pure PROFINET Device functionality is typically accompanied by the
implementation of additional functionality like the integration of switch functionality into the device.
The support of this commonly requested feature requires the addition of an external switch
component.
Alternatively, a PROFINET Device can also be implemented using ASICs from different vendors.
As described in Section 3.1.1, Single Protocol ASICs (which only support the implementation of
PROFINET Devices) as well as Multiple Protocol ASICs are available. Both types of ASICs support
the implementation of the PROFINET RT as well as the PROFINET IRT protocol.
Disadvantages associated with a conventional PROFINET Device implementation are given in
Table 9.
Disadvantage
Performance
Requirements
Cannot be Met
Table 9:
Description
Isochronous data exchange requires special hardware support. This
functionality is not available in off-the-shelf microprocessors.
Disadvantages of PROFINET Device Implementations Using Conventional Implementation Approaches
4.1.3.2 PROFINET Device Implementation Based on FPGA Technology
This section details the discussion from Section 3.2 for the Industrial Ethernet protocol PROFINET.
The implementation of a PROFINET Device based on FPGA technology consists of two main
components as described in Table 10.
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Component
Description
Switch IP Core
The switch IP Core implements standard switch functionality plus
additional switch functionality as required by PROFINET, including
PROFINET IRT.
Protocol Stack
The protocol stack implements the remaining PROFINET Device
functionality. It runs on an IP Core processor16 on top of an operating
system17.
Table 10:
Main Components of a PROFINET Device Implementation Based on FPGA
Technology
Access to the implemented functionality is provided through an Application Programming Interface
as described in Section 3.2.3.4. It provides the necessary functionality to set up and use the
PROFINET communication in a PROFINET Device.18 Typically, the application-related part of the
API is provided in source code and can be easily ported.
4.2 Implementing an EtherCAT Slave Using FPGA Technology
4.2.1 EtherCAT19 Technology
4.2.1.1 System Model
EtherCAT uses standard Ethernet frames but a completely different communication structure idea.
An EtherCAT network consists of an EtherCAT Master and a number of EtherCAT Slaves.
With EtherCAT different topology structures like star topologies, daisy chain topologies and drop
line topologies are supported. These topology variants can be used in any combination. Almost
any number of devices (up to 65,535) can be wired in a line structure. There are no restrictions
due to cascaded switches or hubs.
An overview of different topology structures supported by EtherCAT is shown in Figure 15.
16
17
18
19
For instance, the protocol stack can run on the IP Core processor NIOS II for Altera FPGAs or on the IP
Core processor µBlaze for Xilinx FPGAs.
The Softing implementation uses the operating system eCos.
The Softing Simple Device Application Interface (SDAI) by default supports a 4 KB dual port RAM
interface.
EtherCAT is a patented technology, licensed by Beckhoff Automation.
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Figure 15: Different Topology Structures Supported by EtherCAT
Each EtherCAT frame contains data for the various slaves within the network and its relevant
data is accessed and processed by the individual slave on the fly, resulting in very short cycle
times. When the frame reaches the end of the network, it is sent back to the master directly. The
Ethernet full-duplex mode allows to create a logical ring supporting this communication behavior.
An example of an EtherCAT frame is shown in Figure 16.
Figure 16: Structure of an EtherCAT Frame
4.2.1.2 Device Model
The EtherCAT Slave consists of the EtherCAT Slave Controller and the implementation of the
individual EtherCAT communication protocol features like cyclic synchronous communication and
asynchronous communication. The EtherCAT Slave Controller implements the Data Link Layer
and provides an interface to the EtherCAT fieldbus.
Figure 17 shows the architecture of a typical EtherCAT Slave.
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Figure 17: EtherCAT Slave Structure
4.2.1.3 I/O Data Exchange
EtherCAT exchanges data cyclically. Usually the cyclic frames are for process data and cannot
be modified during system runtime. The cyclic frames depend on the configuration. The EtherCAT
Master is responsible for sending them out. The most widely used software PLC for EtherCAT
usually works with cycle times between 50 µs and 100 ms.
4.2.1.4 Acyclic Data Exchange
Acyclic data can be exchanged as part of the cyclic frames and are also sent out by the EtherCAT
Master. Acyclic data is used to send diagnostic information, mailbox communication or communication within subordinate fieldbuses.
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4.2.1.5 Device Description
The EtherCAT device description file is based on XML and describes the properties of the
EtherCAT Slave. The information contained in the EtherCAT device description file is listed in Table
11.
Component
Description
Vendor
Vendor Information Like Vendor ID, Name, etc.
Device Groups
Organization Units to Help Configuration Tools
Device
Device Information Like Device Type, Name, Process Data Interface
Type, etc.
Process Data Object
(PDO)
Description of RxPDOs (Output Process Data)
and Description of TxPDOs (Input Process Data)
Fieldbus Memory
Definition of FMMU Usage
Manage Unit (FMMU)
Allowed Values:
• ‘Outputs’: FMMU is Used for RxPDO
• ‘Inputs’: FMMU is Used for TxPDO
• ‘MBoxState’: FMMU is Used to Poll Input Mailbox
Size and Address Information Regarding FMMU
Table 11:
Components of EtherCAT Device Description Files
This XML description provided by the device description file can be used by the EtherCAT configuration tool to configure the device and the network. The specification of the file format is defined in
an XSD schema.
4.2.2 EtherCAT Organization and Specification
EtherCAT is a worldwide standard allowing data exchange inside a communication network based
on Ethernet technology. EtherCAT stands for very short cycle times for applications in real-time
environments. Since its publication in 2003 the EtherCAT Technology Group (ETG) is responsible
for the further development.
The ETG has over 2,400 members who can influence the development of the technology in
different working groups.
EtherCAT is an official IEC specification: 61158 – Type 12 (Industrial Communication Networks,
Part 3/4/5/6). Currently EtherCAT is defined by the standards listed in Table 12.
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EtherCAT
Specification
EtherCAT
Specification
ETG.1000.x
Version 1.0.3
International
Standard
IEC61158,
Ed. 4
Title
Industrial Communication Networks - Fieldbus Specifications
EtherCAT Slave
Information (ESI)
Specification
ETG.2000 V1.0.7
ISO15745-4 Industrial Automation Systems and Integration –
Open Systems Application Integration Framework
Drive Profiles
and Mapping to
EtherCAT V1.0
IEC61800-7 Adjustable Speed Electrical Power Drive Systems
Safety over
EtherCAT
ETG.5100 V1.2.0
IEC61784-3 Industrial Communication Networks - Fieldbus Specifications
Profile Sets – Part 3
EtherCAT
Installation
Profile, Version
from May 14, 2010
IEC61784-5 Industrial Communication Networks - Fieldbus Specifications
Profile Sets – Part 5
Table 12:
20
EtherCAT Specifications20
(Source: EtherCAT Technology Group)
The EtherCAT specification overview reflects the status as per June 2015.
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5.
Advantages of Using FPGA Technology for Industrial Ethernet Field Device
Implementation
There are a number of advantages to be gained from using the FPGA technology for implementing
an Industrial Ethernet field device. These advantages are discussed in this chapter.
5.1 Flexibility for Implementing an Industrial Ethernet Field Device
A main advantage of FPGA technology is that it provides a high level of flexibility for implementing
an Industrial Ethernet field device. Different aspects resulting from the provided flexibility are
discussed in Table 13.
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Flexibility Aspect
Description
Supported Scalability
The FPGA image is structured by individual IP Cores which can be
combined into one FPGA providing scalability. Thus, different Industrial
Ethernet field device architectures can be implemented, including
a pure Industrial Ethernet protocol or the additional implementation
of the application processor within the same FPGA and IP Core
processor, respectively (see Figure 2, Figure 3 and Figure 4).
The required FPGA size is determined by the individual functionality to
be supported.
Integration of
Communication and
Application
Depending on the individual requirements, using an FPGA allows to
combine both, communication and application implementation into one
component.
Support of Protocol
Extensions and New
Protocols
The FPGA-based Industrial Ethernet implementation allows to extend
a specific protocol implementation individually as needed. It also
allows to support additional Industrial Ethernet protocols using the
same hardware.
Scope of Implemented The FPGA allows manufacturers to not only implement the Industrial
Functionality
Ethernet field device functionality, but also add individual capabilities
(e.g. access to the backplane bus) according to their specific
requirements. This is done by simply adding the appropriate IP Cores.
Integration of
Interfaces
IP Cores supporting different types of memory interfaces (e.g.
SDRAM, DDR2RAM, etc.) and interfaces for application integration
(e.g. dual port memory, Serial Peripheral Interface, etc.) are available
and can be integrated directly into the FPGA of the Industrial Ethernet
field device implementation.
IP Core Loading Time
FPGAs provide flexibility to load the IP Cores of an Industrial Ethernet
field device. For instance, the IP Cores can be loaded as part of the
field device production. Alternatively, the IP Cores can also be loaded
after installation, making use of the provided IT channel.
Support of
Specification Updates
The functionality provided by an FPGA is not fixed, but can be updated
as required by simply loading the individual IP Core into the FPGA.
This way, for instance, a future specification update can be implemented and used within an existing FPGA hardware.
Upgrade to Next
Technology Level
Device manufacturers are free to decide on a new hardware
generation on the basis of their own individual considerations and
not driven by external factors like the discontinuation of an individual
electronic component. Existing IP Cores can be re-used with nextgeneration FPGAs, and new IP Cores (e.g. supporting a new memory
technology) can easily be added.
Table 13:
Flexibility Provided by Using FPGA Technology for Industrial Ethernet Field Device
Implementation
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5.2 Further Advantages
Besides flexibility there are other benefits in using FPGA technology for implementing an Industrial
Ethernet field device.
One is that with FPGAs, the investment in the Industrial Ethernet field device implementation
is guaranteed for the future: A specific Ethernet hardware component as well as an Industrial
Ethernet field device ASIC are specialized components which are typically only available from a
single manufacturer. Some of these niche products have already been on the market for several
years, which increases the probability of supply bottlenecks and product discontinuation in the
near future, and thus directly impacts the product availability of the Industrial Ethernet field device
implemented based on these components.
FPGAs in contrast are universal mainstream products which are produced and distributed in large
amounts. Their product maintenance is thus of vital interest to FPGA manufacturers. Improvements in semiconductor technology can be implemented very quickly and additional IP Cores, for
instance supporting new memory technologies, continuously become available. Therefore, basing
an Industrial Ethernet field device implementation on FPGA technology ensures its continued
availability in the future.
The easy integration of the Industrial Ethernet field device protocol stack is another advantage
of using FPGA technology. As the environment (i.e. processor IP Core, operating system, and
memory access) is fully defined, the executable format of the Industrial Ethernet field device
protocol stack can be prepared in advance. This eliminates the need to port this protocol stack
to the target platform. All that has to be implemented is the access to the planned application
interface, resulting in significantly less effort.
Within an existing Industrial Ethernet field device implementation, an application like the communication via the backplane bus is often already provided using FPGA technology. Thus, the decision
to use an FPGA for implementing the Industrial Ethernet field device does not require additional
hardware components. Instead, this functionality can be merged into an existing FPGA.
Automation device hardware more and more includes consumer components, e.g. memory. In
comparison to dedicated automation components, consumer components are typically available
only for a short time (3 to 4 years). This makes component obsolescence a real challenge. ASIC
manufacturers guarantee that their products will be available for 10 years and more. However,
they cannot guarantee the availability of the other components used. Thus, it may happen that
new components can no longer be interfaced with the ASICs in use. FPGAs are more flexible here
and allow the manufacturer to make a free choice of components.
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5.3 Support of Different Protocols by One Hardware
Using FPGA technology for implementing the Industrial Ethernet field device allows to support a
set of Industrial Ethernet protocols with just one hardware platform. The selection of the specific
Industrial Ethernet protocol to be used is done by loading the appropriate image, e.g. from the
Flash memory, or by loading a new firmware.
This approach provides additional freedom to hardware manufacturers. It allows using a universal
hardware and application platform to support multiple protocols within several product families.
All in all this results in the effective use of the implementation effort invested and minimizes the
required amount of stock held by the manufacturer.
In addition, the FPGA-based implementation of an Industrial Ethernet device also allows to support
IT services by the device as well. Here standard Ethernet protocols like HTTP or FTP are used
for implementing a transparent IT path using the same infrastructure. For instance, functionality
such as access to device data via a web server and the internet or the firmware download can be
provided by the device.
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6.
Summary
FPGA technology allows implementing a fully functional Industrial Ethernet field device while
offering advantages over a conventional closed implementation.
To sum up the FPGA advantages, a comparison regarding various aspects of an Industrial
Ethernet field device implementation is given in Table 14.21 This comparison addresses the usage
of an FPGA vs. an ASIC or a standard processor.
Topic
FPGA
(see Section
3.2)
ASIC22
(see Section
3.1.1)
Standard
Processor
(Pure Software
Solution)
(see Section
3.1.2)
Full Support of Industrial Ethernet Field
Device Functionality
(Including Ethernet Access Functionality)
+
o
-
Support of Different Protocols by the
Same Hardware
+
o
o
Integration of Application
+
o
o
Scalability
+
o
-
Long-Term Availability of Technology
(Including Successor Products)
+
o
o
Flexibility Regarding Support of Add-On
Functionality
+
-
-
Price of Relevant Components
(Protocols, Processor, PHY, Memory)
+
+
o
Table 14:
Advantages of FPGA Usage in Comparison With Conventional Implementation
Approaches22
(Coverage of Topic: +: Good, o: Neutral, -: Bad)
The FPGA hardware platform which has been developed as part of an Industrial Ethernet field
device implementation also provides additional capabilities. It makes use of a universal hardware
architecture which results in a general platform supporting multiple communication protocols.
21
22
Softing’s FPGA solution allows to make use of the individual advantages presented.
Within this summary table the term ASIC includes Single Protocol ASICs as well as Multiple Protocol
ASICs as described in Section 3.1.1.
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7.
Abbreviations and Acronyms
ALM
Adaptive Logic Module
(Abbreviation refers to Altera FPGAs)
ASIC
Application-Specific Integrated Circuit
API
Application Programming Interface
CPU
Central Processing Unit
CSMA/CD
Carrier Sense Multiple Access / Collision Detection
DDR
Double Data Rate
DMA
Direct Memory Access
DPRAM
Dual Port Memory
ESC
EtherCAT Slave Controller
FPGA
Field Programmable Gate Array
FTP
File Transfer Protocol
GSDML
Generic Station Description Markup Language
(Abbreviation refers to PROFINET protocol)
GPIO
General Purpose I/O
HTTP
Hypertext Transfer Protocol
IP
Internet Protocol
IP Core
Intellectual Property Core
I/O
Input/Output
IRQ
Interrupt Request
IRT
Isochronous Real-Time
(Abbreviation refers to PROFINET protocol)
MAC
Medium Access Control
MII
Media Independent Interface
MM Bridge
Memory-Mapped Bridge
(Abbreviation refers to Altera FPGAs)
Mutex
Mutual Exclusion
PHY
Physical Layer
PI
PROFIBUS & PROFINET International
PIO
Programmed Input/Output
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PLC
Programmable Logic Controller
PLL
Phase-Locked Loop
RAM
Random-Access Memory
SDAI
Simple Device Application Interface
Unified API developed by Softing supporting different communication
protocols including PROFINET and EtherCAT
SoC
System-on-a-Chip
SYSID
System Identifier
TCP
Transmission Control Protocol
UDP
User Datagram Protocol
XML
Extensible Markup Language
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8.
About Softing
The Softing Industrial Automation segment is part of the Softing group founded in 1979.
Softing Industrial Automation is a global specialist in industrial communication technologies such
as fieldbuses and Industrial Ethernet. With over 35 years of experience, Softing’s Industrial
Automation business units deliver connectivity, diagnostic products, and services to customers in
the factory and process automation industry.
The options offered by Softing for implementing an Industrial Ethernet field device are based on
the great technical experience and the high quality resulting from implementing a vast number of
field-proven products and successful customer-specific projects. Thus, for an individual
Industrial Ethernet field device implementation a unique combination of perfectly matched highquality products and professional services is available from a single source. Softing’s relationship
with its customers is shaped by a high degree of flexibility for adaptations to individual requirements as well as by a long-term partnership. A network of sales offices and distribution partners
around the world enable Softing to address individual customer needs in a quick and appropriate
way.
The Softing products are tailored to the requirements of system integrators, device vendors,
machine and equipment manufacturers, or end users and are known for their ease of use and
functional advantages.
Softing Industrial Automation GmbH
Richard-Reitzner-Allee 6
DE-85540 Haar
Germany
Phone: +49 / (0)89 / 45656-340
Fax:
+49 / (0)89 / 45656-488
E-mail:
info.automation@softing.com
http://industrial.softing.com
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9.
Authors
Tobias Heilmeier
Product Manager Factory Automation
Softing Industrial Automation GmbH
Haar (near Munich), Germany
Frank Iwanitz
Product Manager Real-Time Ethernet
Softing Industrial Automation GmbH
Haar (near Munich), Germany
Georg Süss
Product Marketing
Softing Industrial Automation GmbH
Haar (near Munich), Germany
10. References
•
PROFINET Technology and Application – System Description
October 2014
Order Number 4.132
Available at:
http://www.profibus.com/download/technical-descriptions-books/
(as of March 24, 2015)
•
EtherCAT Brochure
November 2014
Available at:
www.ethercat.org/download/documents/ETG_Brochure_EN.pdf
(as of March 24, 2015)
Implementing Industrial Ethernet Field Device Functionality by Using FPGAs
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11. List of Figures
Figure 1:
Structure of Industrial Ethernet Field Device Implementation and Its
Reference to the OSI Layer Model.............................................................................. 4
Figure 2:
Hardware Architecture of Industrial Ethernet Subsystem Implemented on FPGA....... 9
Figure 3:
Allocation of the Industrial Ethernet Communication Protocol and the
Device Application to Two Different Processors Within an FPGA.............................. 12
Figure 4:
FPGA Processor Shared Between the Industrial Ethernet Communication
Protocol and the Device Application.......................................................................... 13
Figure 5:
Use of the FPGA As Communication Processor and Execution of the
Device Application on an External Microprocessor................................................... 14
Figure 6:
Performance Acceleration in FPGA-Based Industrial Ethernet
Implementations Using the DMA Channel................................................................. 16
Figure 7:
FPGA-Based Communication Interface for Implementing an Industrial
Ethernet Field Device................................................................................................ 17
Figure 8:
Lean Calling Structure of the Common Application Programming Interface
for Industrial Ethernet Field Devices......................................................................... 19
Figure 9:
FPGA Design of the Industrial Ethernet Subsystem Together with the
Application Subsystem.............................................................................................. 21
Figure 10: PROFINET Network Structure.................................................................................. 25
Figure 11: PROFINET Device Structure..................................................................................... 26
Figure 12: PROFINET Communication Schedule of I/O Data.................................................... 27
Figure 13: Sources of the GSDML Specification........................................................................ 28
Figure 14: Different Parts of a GSDML File and Their Representation in the
PROFINET XML Viewer............................................................................................ 28
Figure 15: Different Topology Structures Supported by EtherCAT.............................................. 32
Figure 16: Structure of an EtherCAT Frame............................................................................... 32
Figure 17: EtherCAT Slave Structure......................................................................................... 33
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12. List of Tables
Table 1:
OSI Layers and Their Industrial Ethernet Implementation........................................... 2
Table 2:
Advantages and Disadvantages of Using Single Protocol and Multiple
Protocol ASICs for Implementing an Industrial Ethernet Field Device......................... 6
Table 3:
Advantages and Disadvantages of Using the Completely Software-Based
Implementation of an Industrial Ethernet Field Device................................................ 7
Table 4:
Advantages of Implementing an Ethernet Real-Time Access Based on
FPGA
Technology................................................................................................................ 10
Table 5:
Performance Optimization Potential Using the DMA Channel................................... 16
Table 6:
FPGA Resource Consumption of Additional IP Cores Required for an
Industrial Ethernet Implementation........................................................................... 22
Table 7:
Required FPGA Resources for Overall Design, Industrial Ethernet
Subsystem and Industrial Ethernet IP Core of an Industrial Ethernet Field
Device Implementation for Different Industrial Ethernet Protocols............................ 22
Table 8:
PROFINET Specifications......................................................................................... 29
Table 9:
Disadvantages of PROFINET Device Implementations Using
Conventional Implementation Approaches................................................................ 30
Table 10:
Main Components of a PROFINET Device Implementation Based on
FPGA Technology..................................................................................................... 31
Table 11:
Components of EtherCAT Device Description Files.................................................. 34
Table 12:
EtherCAT Specifications........................................................................................... 35
Table 13:
Flexibility Provided by Using FPGA Technology for Industrial Ethernet
Field Device Implementation..................................................................................... 37
Table 14:
Advantages of FPGA Usage in Comparison With Conventional
Implementation Approaches...................................................................................... 40
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