Interaction of SystemC AMS Extensions
with TLM 2.0
Markus Damm, Christoph Grimm
Institut für
Computertechnik
ICT
Vienna University of Technology
Martin Barnasconi
NXP Semiconductors
Institute of
Computer Technology
10.03.2016
1
Embedded AMS systems
Receiver
Modulator/
AMS-TLM
demod.
DSP
interface
Serial
Interface
ADC
Calibration & Control
Antenna
front-end
SystemC AMS
Transmitter
DAC
RF
detector



Microcontroller
Temp.
sensor
Oscillator
Host
processor
SystemC TLM
Memory
Imaging
DSP
Audio
DSP
High
Speed
Serial
Interface
to all blocks
Clock
Generator
Power
Management
Tight interaction between AMS and digital HW/SW sub-systems
Dedicated interfaces between analog and digital domain
How should a TLM AMS interface be defined?
Institut für Computertechnik
10.03.2016
2
SystemC AMS TDF
…implies a samling
period of 20 s here!
Sine-source
e.g. sampling
period of 2 ms
here…
A
B
50
20
s
20
s
100
1
1
Bit-source
C
100
20
s
20
2 ms
Modulation
2 ms
data rates
s
1
D
Environment
“TDF-Cluster“
Schedule: B A A C D…D
100x



Timed DataFlow – Synchronous Dataflow with timing annotation
Enables static scheduling – fast simulation of sampled analog
signals at discrete time points
Sampling period associated to token production/consumption
Institut für Computertechnik
10.03.2016
3
SystemC AMS – SystemC synchronization




SystemC AMS has its own execution semantics and
simulation time  synchronization needs!
SystemC AMS provides converter ports which allows TDF
modules to connect to usual SystemC Discrete Event signals.
Accessing these ports triggers synchronization to SystemC kernel
Note: SystemC AMS is temporally decoupled, similar to the
TLM 2.0 loosely timed coding style!
tTDF
26 ms
32 ms
38 ms
26 ms
32 ms
38 ms
TDF-module
2 ms
token
valid at 26 28 30 32 34 36 38 40 42 ms rate 3
3 ms
rate 2
26 29 32 35 38 41 ms
tDE
20 ms
38 ms
20 ms
38 ms
synchronization
tTDF ↔ tDE
Note that tTDF  tDE always holds!
Institut für Computertechnik
10.03.2016
If the data rate is > 1, the data
token even “warp ahead“ tTDF !
4
Requirements for AMS-TLM interface

Avoid “signal-level” interface (DETDF converter ports) between
AMS and TLM



Create direct interface between AMS Timed Data Flow and TLM
2.0 Loosely-timed coding style



avoid unnecessary kernel context switching
maintain concept of “loosely coupled independent processes”:
avoid strict timing synchronization between processes
maintain temporal decoupling for both engines
efficient packing an unpacking of “analog samples” (data) in/from
transactions
Introduction of specialized converter modules / channels


can be instantiated and configured by the user
part of design refinement methodology
Institut für Computertechnik
10.03.2016
5
Basic idea of a generic TLMTDF converter
TLM
Interconnect





TLMTDF
converter
input-buffer
dummy
DE signal
output-buffer
TDF
TDFCLUSTER
TDF
sub
module
sub
mod
ule
DETDF
converter
port
WRITE transaction data is streamed to TDF cluster directly
Incoming TDF “samples” are passed to READ transactions
The converter has to be part of the TDF-cluster
Transactions mostly won’t come in regularly  We use buffers
which are accessed via transactions
The TDF cluster might run ahead too far in time
 We need synchronization means!
…and: what means “too far” exactly?
Institut für Computertechnik
10.03.2016
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Implementation

Our current conversion approach assumes loosely timed initiators



Blocking interface, no backward path used
Initiators may use temporal decoupling
Issues:



Transactions may arrive out of order (delays)
 we need buffers which also keep timing information
If a write-transaction has a delay annotation, the converter doesn’t
know if the buffer has enough space by that time
 we need a projected free buffer space concept
TLM and TDF might warp ahead too much of each other
 we need to trigger synchronization
Institut für Computertechnik
10.03.2016
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TLMTDF converter implementation
WRITE-transactions 
TLM
Interconnect
TDF
TLM  TDF
converter
sub module
TDFCLUSTER
output-buffer

The output buffer keeps the timestamp of the transaction the
respective data was sent with (similar to payload event queue).




If the TDF sub-module fires, it uses only data with a
timestamp  the current SystemC AMS time
If an incoming transaction has a delay > 0, a projected free buffer
space is computed
the transaction is returned with an error if the (projected) free
buffer space is too small for the data
Synchronization: buffer underrun
Institut für Computertechnik
10.03.2016
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TDFTLM converter implementation
READ-transactions 
TLM
Interconnect
TDF
TDF  TLM
converter
sub module
TDFCLUSTER
input-buffer

If the TDF submodule fires, the incoming data token are copied
into the input buffer (usual FIFO).




We store only the timestamp of the oldest buffer token
Transactions are annotated with an delay according to the
timestamp of the youngest token returned
If buffer holds not enough data for the read request, an error is
returned
Synchronization: buffer overflow
Institut für Computertechnik
10.03.2016
9
Conclusion / future work

Connecting TLM2 and SystemC AMS models makes sense
regarding the design of mixed signals SoCs


Efficient communication between AMS and digital HW/SW part
Sophisticated synchronization

TLM2 temporal decoupling processes can work well together
with SystemC AMS statically scheduled TDF processes.

The presented work is a technical feasibility analysis, more
groundwork has to be done.


Study Approximately-timed initiators and converter channels
Apply methods to Real-life demonstrator
Institut für Computertechnik
10.03.2016
10
Thank you
for your
attention!
Your:
 questions
 comments
 ideas
 objections
Institut für Computertechnik
10.03.2016
11