In an effort driven by European semiconductor companies and
universities, the Open SystemC Initiative (OSCI) last week announced
the first version of the SystemC analog/mixed-signal language standard, AMS
1.0. Since Cadence is the industry leader in mixed-signal design and verification,
and is strongly promoting a transaction-level modeling (TLM) based design and
verification flow on the digital side, it's natural that folks at Cadence would
take an interest in this development.
The message I get from our mixed-signal team is that while
it's too early to speak of any potential support plans, Cadence is watching
this development carefully and is seeking to learn more about the proposed
standard and its current and future applications. We are reviewing closely the
use of SystemC AMS, how it compares to other mixed-signal behavioral modeling
approaches, and what the level of customer interest is.
Some background and commentary about SystemC AMS follows.
What it's all about
With increasing analog and mixed-signal content on systems-on-chip,
design teams are looking for faster ways to run system-level simulations. They
also need to incorporate mixed-signal functionality into system-level design
and architectural exploration. Spice and Fast Spice are too slow for full-chip,
top-level verification, and even languages like Verilog-AMS can pose a
According to the OSCI announcement, SystemC AMS extends the
SystemC class library to provide functional modeling, architectural
exploration, virtual prototyping, and integration validation for "embedded
analog/mixed-signal systems." The extensions are intended to help engineers
understand the interaction between hardware/software and mixed-signal
subsystems at the architectural level.
A SystemC AMS
whitepaper points out that system-level tools such as Simulink are often
used for functional modeling but don't target architecture. It adds that
Verilog-AMS and VHDL-AMS don't support hardware/software co-design at a high
level of abstraction, and that co-simulation that mixes SystemC and Verilog-AMS
or VHDL-AMS does not provide sufficient performance.
The whitepaper describes three types of SystemC AMS
The SystemC AMS 1.0 language reference manual (LRM) and
associated documentation can be downloaded from the OSCI web
site. Meanwhile, a 2009 article
by Martin Barnasconi of NXP, OSCI AMS working group chair, provides more detail
about modeling formalisms. The article notes support from NXP,
STMicroelectronics, and Infineon in addition to several universities.
Questions and commentary
The basic idea behind SystemC AMS is right - mixed-signal
design and verification need to move to higher levels of abstraction in order
to run much faster. "When we talk about a system strategy, we need to make sure
we include analog," said Andreas Kuehlmann, director of Cadence
Research Labs. "To simulate any functionality, you need to simulate analog
components together with software, processors, DSPs and so on."
There are, however, a number of practical questions, such as
what one can and cannot do with transaction-level modeling in the analog world.
Another question is what capabilities SystemC AMS might provide compared to other
analog modeling approaches for high level design and verification, like
Verilog-AMS wreal and VHDL real, and mixed language approaches like the
combination of SystemC with Verilog-AMS/VHDL-AMS in a true mixed-signal
As noted in a recent
whitepaper, real number models can represent analog behavior in a digital
context, and the Cadence Incisive
Enterprise Simulator can then run wreal and real models in a pure digital
environment with all the advantages of high performance and metric-driven
AMS Designer can deal with mixed-language scenarios including SystemC,
Verilog-AMS, VHDL-AMS, and Spice, providing a smooth path down to
transistor-level implementation if needed.
So far, most of the push behind SystemC AMS has come from a
few large European semiconductor companies, especially NXP, and academia. Now
that the standard is out, will the interest extend more broadly? "As part of
our interest in system-level analog modeling, this [SystemC AMS] is one of the
options we will carefully monitor," Andreas said.
Feedback from analog/mixed-signal designers is very welcome!
We have worked out a solution consisting of high level simulation using Timed Data Flow Model of Computation in SystemC AMS and Cadence Incisive. We use our setup for cosimulating implementable models in Cadence IUS with the SystemC AMS specification models. Please check "Fast and Unified SystemC AMS - HDL Simulation" for rationale, "On Mixed Abstraction, Languages, and Simulation Approach to Refinement with SystemC AMS" for simulation based digital model refinement and "Analog Behavior Refinement In System Centric Modeling " a solution for cosimulating analog models with SystemC AMS. The scheme uses PLI interface for accessing simulation data. Once VHPI-AMS has been approved by IEEE and implemented in Incisive we would be able to directly probe continuous time nets. Until then analog event based modeling and conventional real valued discrete time object access is the solution.