1 Extending FPGA Verification Through The PLI Charles Howard Senior Research Engineer Southwest Research Institute San Antonio, Texas (210)

HowardMAPLD2005/1932 Background Verilog is a hardware description language for digital logic design (FPGA/ASIC/PLD) Typical usage –Design End item design description (RTL for synthesis) –Verification Modeling input interfaces (providing proper data/control relationships) Generation of test stimuli, esp. for low-level verification activities. Robust & simple first order DV with standard tools –Not adequate with growing complexity, multiple devices

HowardMAPLD2005/1933 Low-level Verification Results of this first order modeling are often verified by visual means –Finite limitation on the amount of transactions that can be verified visually Rudimentary checking of interface protocols in Verilog models –Repetitive pattern detection –Interface timing Verilog checkers increase verification capabilities tremendously –Directed tests are excellent for nominal function –Perfect for small number of scenarios It is at this point that the real strength of Verilog is revealed – the programming level interface (PLI).

HowardMAPLD2005/1934 The Verilog PLI The Programming Language Interface is a procedural interface between Verilog simulation and other software programs –Verilog models can invoke external program during simulation Accessibility to every attribute within the simulation structure Capability to read and/or modify any value in the simulation Flexibility to perform any simulation task –Initializing memories at simulation start –Verifying end of simulation results.

HowardMAPLD2005/1935 A Few PLI Applications PLI can be used to link any type of application to the simulation –Delay calculators –Custom displays –C language models –Hardware modelers –Co-simulation environments –Reading test vector files –Custom user interfaces –Design debug utilities

HowardMAPLD2005/1936 PLI Implementations C programs can be tied through the PLI to Verilog shell models C programs then used to: –Dynamically generate test stimuli –Check design outputs –Scoreboard non-linear data flows –Incorporate random features Layered approach –Sequences and scenarios Random and directed –Coverage

HowardMAPLD2005/1937 PLI Advantages Simulations do not need to be limited –Time, complexity or randomness Extended to reflect the real world More simulation cycles can occur Capability to randomize each test Coverage –Regression tests

HowardMAPLD2005/1938 PLI Goal In short, the PLI allows the designer to build a robust virtual test bench that allows the functional interaction of hardware and software to first be characterized without lab space. –Recent experiences (what I have learned in the customer’s lab) Flow Control from multiple sources FSW access order

HowardMAPLD2005/1939 Randomization An immense number of HW/SW interactions can be characterized for flaws Using random and directed test techniques, functional verification of the logic design can be extended far beyond first order techniques. Resulting design is much more robust and likely to function when moved into silicon.

HowardMAPLD2005/19310 Our approach PLI extension of FPGA verification capabilities Development of several key bus functional models and PLI routines Specific approaches and examples will be presented.

HowardMAPLD2005/19311 Verification Environment Simulations –Each FPGA undergoes directed simulation at the chip level. Verifies logic, timing, and functionality –FPGAs are integrated into a larger multi-FPGA, board level simulation as they are completed. Verifies processor -> local bus traffic Verifies inter-FPGA local bus traffic

HowardMAPLD2005/19312 Board Verification Board GSE is designed to verify board level requirements. –Mixture of automated and manual measurements. Board Test Cases have been defined based on PFS –Basis for PLI functions IR&D funds for enhanced simulation environment –Three fundamental testing blocks: cPCI Telemetry RX Serial command TX

HowardMAPLD2005/19313 PLI Verification Environment cPCI –Memory peeks / pokes, config cycles, resets –Exhaustive memory tests, VTC duration testing, serial command verification, telemetry packet generation, 1553 traffic, access order dependencies, etc. Telemetry RX –ASM detect, de-randomization, frame length check –Frame integrity, FHP check, packet integrity, data integrity Telecommand TX –Inject telecommands, monitor response –Error injection, data integrity (PCI side)

HowardMAPLD2005/19314 Results Simulation run length Coverage metrics COME ON, NOW, REALLY… I’m still working on this, and trying to bring up hardware in the lab!!!