Standards are living, evolving entities, and SystemC -- standardized in 2005 as IEEE 1666 -- is no exception. This language, which has become indispensable for virtual platforms, high-level synthesis, and transaction-level modeling (TLM) design and verification, is undergoing a new revision this year. Here's a brief preview of what to expect.
Every IEEE standard must be reviewed at least every five years, and updated if necessary. In 2010, the IEEE 1666 working group developed a language reference manual (LRM) for an updated version of SystemC, which is currently under review by the working group. Main features of the update include:
- Inclusion of the Open SystemC Initiative (OSCI) TLM-1 and TLM-2 modeling standards into the IEEE 1666 SystemC LRM
- Addition of process control constructs
- Addition of named events
- A large number of small enhancements and corrections
Stan Krolikoski, group director of standards at Cadence, chairs the IEEE 1666 working group. He expects that the new revision (P1666-2011) will go to ballot late in the first quarter of 2011, and will probably attain full confirmation as an IEEE standard by the end of 2011. He noted that representatives from over 25 companies actively participated in the standards update.
While the inclusion of TLM-1 and TLM-2 in P1666-2011 represents the IEEE stamp of approval, it doesn't result in significant core language changes. Two features that do result in language changes, process control constructs and named events, are described further below. Thanks to Stuart Swan and Bishnupriya Bhattacharya of Cadence, both of whom have been heavily involved with P1666-2011, for providing the following information.
Process Control Constructs
Processes are the basic behavioral entities in SystemC, and they run under the control of the SystemC kernel scheduler. An application can influence how and when a process is scheduled, but prior to P1666-2011, SystemC lacked a direct API for controlling one process from another. The new process control constructs make it possible for one process to suspend-resume, disable-enable, or kill/reset another.
The new constructs facilitate testbench modeling. For example, with a complex stimulus generator, you might want to have one block suspend stimulus generation for a period of time, then resume it. Process control constructs also make it easier to model low-power systems where transitions are occurring between different power modes.
Another important use of process control constructs is to allow modeling of asynchronous resets or triggers. For example, a graphics co-processor inside a laptop computer may be in the middle of some graphics processing when the laptop goes from AC power to battery power. The co-processor may need to immediately switch to a low-power mode. One way to model this is to allow a process to throw a user-defined C++ exception into another process. This capability is provided by the new constructs.
Process control constructs are based on a specification written by Cadence and submitted to OSCI several years ago. They are already supported in the Cadence Incisive Enterprise Simulator. A Cadence paper describes further details.
Objects in SystemC have hierarchical names that are distinct from variable names, a feature that is very useful in debugging. But events in the 2005 SystemC standard do not have names. The event naming proposal originated by Cadence rectifies this discrepancy, making it much easier to track events during debugging. The named events feature is currently implemented in the Incisive Enterprise Simulator.
After the IEEE standardization process is finished, Stan noted, the ball goes back to OSCI, which will develop the next contributions to the IEEE. Meanwhile, OSCI is continuing to work on aspects of SystemC that are not currently part of the IEEE standard, such as analog/mixed-signal extensions and a synthesizable subset. A brief overview of OSCI working groups is available here.
A standards-based ecosystem is a crucial part of the EDA360 vision. And few standards are as important to that ecosystem as SystemC. P1666-2011 is thus a significant milestone for the EDA and semiconductor industries.