Rappit
Framework for Synthesis of
Host-Assisted Scripting Engines for
Adaptive Embedded Systems
Jiwon Hahn, Qiang Xie, Pai Chou
Center for Embedded Computer Systems,
UC Irvine
CODES+ISSS
September 22, 2005
Embedded Systems
Host-involved
Standalone
GPS tracer
Toy
ATM
Medical Device
Sensor-net
Embedded
Set-top box
Copier
SD
systems
Printer
Battery emulator
SD
Disk drives
Smart-UPS
Hybrid
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RATE
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Vending
machine
MP3 player
Cell phones
Digital camera
PDA
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Embedded Systems Programming
Current Methodology
Low-level programming (e.g., C, assembly)
Single processor, platform specific approach
Unchanged for decades!
Drawback
Time consuming on re-inventing low-level abstractions
eg., registers, timers, interrupts, I/O ports
Error prone
Requires frequent firmware update
Programming flash or burning EEPROM
In-field configuration unsupported
Not adequate for emerging large-scale, distributed, adaptive
embedded systems
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Our Solution: Scripting
High-level programming
Human readable
Utilize platform-independent APIs
Productivity gain
Interactivity
Easy communication between user and platform
Enables efficient test/debugging
Reconfigurability
No compilation or F/W update required
In-field configuration
Code size reduction
Scripts are usually x5 to x10 shorter than C code [Ousterhout]
Reduce memory size & cost, power
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Comparison of design flow
Traditional: 6-stage debugging cycle
F/W coding
Enter bootloader
mode
Compile
Execute
Erase Flash
Load Program
Verify Flash
Restart Board
Scripting: 3-stage debugging cycle
Load script
Write script
Synthesize
scripting
engine (F/W)
Compile
Restart Board
Execute
5
Enter bootloader
mode
Erase Flash
Load Program
Verify Flash
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Scripting vs. Runtime Overhead
Scripting for General Purpose Computers
Assume unlimited resources
Full feature scripting engine for convenience
Slower than system programming language
Scripting for Embedded Systems
Limited memory, CPU, power, …
Need scripting engine optimization
Host assist
Language subsetting
Library subsetting
Efficient memory usage
Scripting may be even faster than compiled code!
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Outline
Related Work
Our Methodology
Code Synthesis
Runtime environment
Experimental Results
Conclusion
Future Work
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Related Work
Name
Platform
Language
H I
PyBAR
Router
Python
Y Y Y N/A
x10
SensorWare Sensor
tinyTcl
Y Y Y >237K
‘high’
Mate
Sensor
asm-like
Y Y 17K
‘low’
Agilla
Sensor
asm-like
Y Y 45K
‘low’
Luxdbg
General
Tcl
Y Y N >237K
x10.6
Rappit
General
Python-like
+ APIs
Y Y Y 1K-17K None
* H: High level
I: Interactivity
R C
R: Reconfigurability
PO
C: Code size
PO: Performance overhead compared to compiled implementation
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Overview of Rappit Runtime System
Target System
Host
Rappit S/W
Application
Script
Wired/Wireless link
#include <stdio.h>
void main(void)
{
int a;
.
.
For(i=0;i<2;i++)
{
.
a =b * c;
}
.
.
return;
}
Rappit F/W
Device Drivers
H/W Device
Provide user one integrated environment
of the host and target systems
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Runtime Flow
10
Scripting Engine
(ack)
Scripting Engine
msg
Depacketizer
Packetizer
(cmd)
Packetizer
I/O
GUI
msg
Depacketizer
Response
Msg Generator
I/O
Parser
Script
Parser
Command
Target
Platform
Comm
Link
Host
Platform
Control
Platform
Response
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Scripting Engine Optimization
Language Subsetting
Host Assist
“print reg1”
• User friendly
Host Parser/
Msg. gen.
“0x4A0x01”
• Easy to parse at node
• Efficient command representation
Library Subsetting
Full-Featured
Component Library
(compact packet size and runtime repr.)
Customized Library
MCU
Interrupts RF
RF
Dataflash
SPI UART GPIO Interrupts ADC
LCD
Joystick
Sensor1 Sensor2
11
GPIO
UART
ADC Sensor1
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Our Methodology
System
Description
1. Code Synthesis Flow
2. Runtime Flow
Code
Synthesizer
Script
GUI
HostAssisted
Parser
12
Component
Library
MCU
Scripting
Engine
Application
Primitives
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I. Code Synthesis
Input
Architecture
Application
Communication
Description
Description
Description
Code
Synthesis
Interactive
Language
Output
Host S/W
(Parser,
MsgGen,
Compatible
GUI, …) Message format
Host
13
Component
Library
Target F/W
(Scripting
Engine,
Native
Routines, …)
Binary
Executable
Target
System
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I. Code Synthesis Packet Format Examples
Command Packet Format
Dest.
Msg ID
Opcode
Arg1
Arg2
Arg3
CRC
Command Message Format
Response Packet Format
Src.
Msg ID
Msg Type
Data Type
Payload
CRC
EOP
Response Message Format
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II. Runtime Environment
Host
IDE
Parser
Cmd
prompt
GUI
Component
Library
Msg
Gen.
MCU
Packetizer/ packet Packetizer/
Dispatcher
Depacketizer
Packet
Manager
Admission
Controller
Scripting
Engine
Native
Routines
command
response
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II. Runtime Environment –
Scripting Examples
Interactive port setting
>>
>>
>>
0
>>
>>
1
PORTA[2] = 1; PORTA[2] = 0 # toggle clock
PORTA[1] = 1 # set port A pin 1
PORTA[0] # read input pin
PORTA[2] = 1; PORTA[2] = 0 # toggle clock
PORTA[0] # read input pin
System configuration
>> mcu.sysclock = 1 MHz # set system clock speed
>> uart.baudrate = 9600 bps # set baudrate for UART
>> rf.power = -5 db # set RF tx power
>> rf.speed = 1 Mbps # set RF throughput
>> rf.config # query the configuration
{’payload’: 1, ’power’: -5, ’speed’: 1000000, ’channel’:
100, ’mode’: ’TX’}
Scheduling
>> every(50 ms, ’sample’)
>> stop(’sample’)
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Experimental Setup I
AVR Butterfly board
Atmel ATmega169
8-bit MCU @ 8MHz, 512B
EEPROM, 1KB SRAM,
16KB program flash
Connected to dataflash,
speaker, sensors, joystick, LCD
USART serial link at 9600 baud
AVR Butterfly w/ Wireless module
AVR Butterfly
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Experimental Setup II
HC12 Controller in Mini-FDPM
FreeScale16-bit MC9S12NE64
16KB RAM, 64KB program flash
SPI, I2C, GPIO, ADC
Built-in Ethernet
Mini-FDPM
Laser 1
RF
Filter
Switch
Laser 2
Filter
Mixer
Amp Power
Divider
Laser 3
Local
Oscillator
Broadband
Oscillator
1
Power
Coupler
Mixer
Laser 4
Broadband
Oscillator
2
Amp
Filter
TCXO
Phase
Detector
Mixer
16bit microcontroller
with ethernet
Power
Splitter
Crystal
Filter
Amplitude
Detector
HC12
Host Computer
Ethernet
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Metrics and Modality
Observation Metrics
Metric
Unit
Code size
Bytes
Execution Speed
Cmds/sec
Execution Modality
Modality Approach Programming Method
Native
Compiled
Program the firmware onto the Flash
Batch
Scripting
Preload a script program onto the RAM
Interactive
Scripting
Send one line of command to the RAM
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Experimental Results - Code Size
Experiment
Test code included 100 cmds,
9
instruction types
Same subroutines and packet
handlers used
Code size observed from compiled
code and memory map
Result
Scripting engine is a thin layer
Rappit achieves big reduction in
application code size
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Experimental Results - Execution Speed
Experiment
Relative comparison by setting
host timer with same conditions
Same experiment repeated
several times
3 different applications
Result
Batch mode scripting can be
faster than native!
Same pattern observed in other
experiments
Observed up to 25.7% speed-up
Memory access could be the key
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Summary of Results
Code size reduction
Application
Native
Rappit
Reduction
Reg setting
4.356 KB
1.664 KB
61.8%
LCD usage
12.45 KB
4.2 KB
66.3%
Performance overhead components analysis
Native
Interactive
Batch
Communication
1
3
1
RAM Access
3
1
1
ROM Access
3
1
1
2: tolerable
Packetization
1
2
2
3: slow
Interpretation
1
2
2
(bottleneck)
Total cmd/sec
92
4.75
111
22
1: fast
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Conclusion
Scripted the embedded systems
High-level programming
Interactivity
Reconfigurability
Code size reduction
Overcame scripting overhead
Host assistance
Script subsetting
Library subsetting
Effective memory usage
Synthesis
Systematic generation of scripting environment
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Future Work
More dynamic scheme
Allow new native code to be added
Mapping to richer set of syntax
Eg., http to allow access as web device
Memory management in the target
Set evaluation order to reduce memory usage
Parser optimization
Parsing simplicity vs. expressiveness
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Thank you!
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Backup Slides
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Code Size of Each Rappit Components
Host Code (.py)
Lines Size (KB)
MCU Code (.c)
Lines Size
(KB)
GUI
644
21.8
Cmd
127
2.87
Interpreter
260
-
Parser &
Msg Generator
221
4.97
Primitives
90
-
300
-
263
6.396
Packetizer &
Depacketizer
Library
Packetizer &
Depacketizer
82
2.0
Total
750
1.484
Packet Mgr
42
0.92
Total
1379
38.96
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Goals of Embedded Systems
Fast development cycle
High Adaptability
Embedded
System
Low power
Goals
Low cost
Small size
High performance (speed)
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I. Code Synthesis
Input: system description script
# example: pin mapping for an RF module
mcu = MCU(ATmega169)
# instantiate an atmega169 MCU
import RF
# load a transceiver module
rf = RF(nRF2401)
# instantiate nRF2401 transceiver
rf.CS = mcu.PORTB[0]
# connect the chip select pin
rf.CE = mcu.PORTB[1]
# connect the chip enable pin
rf.DR1 = mcu.PORTB[2]
# connect the data ready pin
rf.CLK1 = mcu.PORTF[1] # connect the clock pin
rf.DOUT1 = mcu.PORTF[2] # connect the data pin
Output: Rappit software for host,
ware for the target platform
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firm
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I. Code Synthesis
Command Format
Machine-efficient representation of a command
Application-specific
Pain to reinvent for each application
Need auxiliary code to handle each command format
Automatic Command Format definition
Synthesizer generates the command format
Coherent between host and target
End user syntax parsed and mapped to command format in the
host parser
Command format interpreted by the target scripting engine
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