Interactive Analog/Digital Mixed Signal Modeling via Foreign VHDL/Verilog C Interface

PLI interface, initially designed for Modelsim environment was successfully tested with NCSim in Linux/Sun environment. Compared to VHPI, PLI revealed to be faster and less memory demanding; furthermore it is suitable for almost every digital simulator able to run mixed VHDL/Verilog simulations.

Real Time Interactive Web GUI

Thanks to the PLI interface, final version of the simulator can be compiled in both Modelsim and NCSim environments.

To facilitate the usage of such simulator, a web GUI was developed, so allowing, independently from the adopted operating system, to use a digital simulator running on a server and to modify simulation parameter values in real time. At the end, the tool acts just like a ‘live datasheet’. Java language was used for the web GUI, this due to the possibility to use many functions for telnet, ssh or ftp. The only prerequisite for the end user is to eventually install the java run time environment, which is freely available for the most common operating systems.

When the simulation starts, the web GUI connects to the server via ssh, checks for licenses and starts Modelsim or NCSim digital tool. Parameters are passed to the simulator by means of a text file via ftp. Every plotting step (e.g.20ms) simulator checks for parameters and plots values. The Registers Page of the user interface allows the user to act as a micro, giving the possibility to send and receive SPI commands, force some faults and see results in real time, in an explicit view (by means of colored flag) or in a more detailed view where every single register bit is showed (Fig. 4 and Fig. 5). When the simulation starts, the web GUI connects to the server via ssh, checks for licenses and starts Modelsim or NCSim digital tool. Parameters are passed to the simulator by means of a text file via ftp. Every plotting step (e.g.20ms) simulator checks for parameters and plots values. The Registers Page of the user interface allows the user to act as a micro, giving the possibility to send and receive SPI commands, force some faults and see results in real time, in an explicit view (by means of colored flag) or in a more detailed view where every single register bit is showed (Fig. 4 and Fig. 5).

For example, a Vcc1 under voltage fault is forced and a change in the LED Current set point value applied (Fig. 6).

As consequence of the former action, some flags related to Vcc1 became red, thus indicating a warning or an error involving this parameter and the Global Error Flag (GEF) as well. The latter action leads to a SPI frame sending for every variation of the set point of the current flowing through the LEDs chain. In the picture both the current set point (in blue) and how the device is behaving (in red) are visible.

In another window (SPI Interface) all the SPI frames are recorded and a batch sequence of SPI frames can be programmed to be sent at specific time (Fig. 7).

Conclusion

A/D Mixed mode simulation was done for commercial STMicroelectronics L99LD01 High Efficiency Constant Current LED Driver, converting Simulink analog parts to C and interfacing them to digital simulator via VHDL/Verilog foreign C architecture. With this unique mixed-signal simulation environment, based only on Modelsim or NCSim digital tools, users are able to simulate A/D mixed models.

A solution for complete standalone environment is under evaluation. To do this, in addition to the analog part model conversion into a Code (ex. C/C++), able to be compiled and made executable in a standalone file, VHDL/Verilog code conversion is required as well, in the same language. At present the L99LD01 digital code has been manually converted into an embedded Matlab function, from this to C code and then integrated with the C code related to the analog parts. The conversion of VHDL/Verilog code is the real bottle neck of the entire process. An automatic tool could represent a huge improvement in the direction of developing A/D mixed mode simulators in standalone format.

References

[1] Matlab, Simulink and Simulink Coder manuals
[2] Modelsim SE Foreign Language Interface manual – Version 6.4
[3] 1364-2005 IEEE Standard for Verilog Hardware Description Language
[4] The Verilog PLI Handbook, Stuart Sutherland, Sutherland HDL, Inc. (partially available on Google book)
[5] Modelsim VHPI/pli/vpi examples
[6] Mixed-signal modeling using Simulink based-C, Shoufeng Mu – Michael Laisne, Qualcomm Inc
[7] Java – Netbeans user guide