{"id":1355,"date":"2020-03-01T17:08:00","date_gmt":"2020-03-01T16:08:00","guid":{"rendered":"http:\/\/www.fabienm.eu\/flf\/?p=1355"},"modified":"2020-03-04T17:08:54","modified_gmt":"2020-03-04T16:08:54","slug":"test-your-chisel-design-in-python-with-cocotb","status":"publish","type":"post","link":"https:\/\/www.fabienm.eu\/flf\/test-your-chisel-design-in-python-with-cocotb\/","title":{"rendered":"Test your Chisel design in python with CocoTB"},"content":{"rendered":"\n

Chisel<\/a> is a hardware description language embedded in Scala<\/a> language. Compared to VHDL\/Verilog Chisel it’s a high-level language. With Chisel it’s easier to parametrize and to abstract your hardware. It’s the language used for all SiFive<\/a> RISC-V cores and for Google Edge TPU<\/a>.<\/p>\n\n\n\n

What’s great with chisel that it generate Verilog sources for synthesis. And we can use this Verilog generated design for simulation or formal prove<\/a>. <\/p>\n\n\n\n

Simulation can be done in Scala with chisel.testers<\/a>. But this tester is mostly under development project for the moment. And there is no test library for common busses and devices like SPI, Wishbone, AXI, PWM, …<\/p>\n\n\n\n

CocoTB<\/a> is a cosimulation testbench framework written in Python<\/a>. Main advantage of CocoTB is that you write your testbench stimulis in python language. Python is really comfortable programming language. The other advantage of using CocoTB is that there is a growing library<\/a> of modules available to test devices like SPI<\/a>, Wishbone<\/a>, USB<\/a>, uart<\/a>, … And its easier to use a library than to reinvent the wheel.<\/p>\n\n\n\n

Then, let’s write Chisel testbench with CocoTB !<\/h4>\n\n\n\n

As an example we will use the ChisNesPad<\/a> project (yes, same as formal prove article<\/a>). <\/p>\n\n\n\n

The directory structure is following :<\/p>\n\n\n\n

\/\n|-- build.sbt  <- scala build configuration\n|-- src\/   <- all chisel sources\n|   |-- main\/\n|       |-- scala\/\n|           |-- chisnespad.scala <- Chisel module we will test\n|           |-- snespadled.scala <- \"top\" module to test with\n|                                    tang nano (gowin)\n|-- formal\/   <- formal directory \n|-- platform\/ <- some usefull files for synthesis with \n|                final platform (gowin).\n|-- cocotb\/   <- python cocotb tests\n    |-- chisnespad\/ <- test for chisnespad core\n    |   |-- Makefile    <- makefile to compile and launch simulation\n    |   |-- test_chisnespad.py <- cocotb stimulis\n    |-- snespadled\/ <- test for \u00abtop\u00bb project that toggle leds\n        |              when push buttons\n        |-- Makefile\n        |-- test_snespadled.py<\/code><\/pre>\n\n\n\n
To launch tests we needs following dependencies :<\/p>\n\n\n\n