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README.md

Overview

This directory contains the testing framework for the Risc-V core.

  • The top testbench file tb.sv instantiates the core and creates log files
  • module_top.sv imports a memory file with a pre-compiled program to the main memory. An example memory.txt is located in this directory

To run the simulation on Modelsim/Questasim 2 script files are provided.

  • Open Questasim and navigate to the sim directory
  • Execute do compile.do to build the RTL and enter the simulation
  • A wave window will appear with pre-loaded signals, stated in the wave.do file
  • Run the simulation, 2 log files with be created and updated with information on the commited and flushed instructions commits.txt and flushes.txt
  • The tb.sv tries to detect when the programs finishes or crashes, by detecting consecutive jumps to the same PC address. While this detection generally works, it might fail depending on the PC alignment and branch predictor training

We use 2 flags on the RTL

  • MODEL_TECH to include the structs.sv, this is defined by default on Questasim
  • INCLUDE_SVAS to include the related sva, this is defined optionally on compile.do

Compile C code and generate Memory File

This directory contains various examples. We provide precompiled files (*.elf) and the equivalent memory files (memory.txt). Bellow we also provide instructions on how to generate your own files.

Before compiling you need

  • the RISC-V GNU Compiler Toolchain (link). Clone the repo and install by running
./configure --prefix=/opt/riscv --enable-multilib
make
  • a utility named elf2hex (link) provided by sifive to convert the elf file to a supported memory file. Clone the repo and follow the instructions
git clone git://github.com/sifive/elf2hex.git
cd elf2hex
autoreconf -i
./configure --target=riscv64-unknown-elf
make
make install
  • a linker script, lscript
  • a bootloader assembly code that calls the main()
  • the C code

Compile

riscv64-unknown-elf-gcc -march=rv32im -mabi=ilp32 -T lscript  bootstrap.s notmain.c -o hello.elf  -nostdlib
  • Replace notmain.c with your own C files and modify the lscript and bootstrap.s
  • include flags, for example optimization (-O)
  • Tested with version riscv64-unknown-elf-gcc (GCC) 8.2.0

Convert elf to memory

riscv64-unknown-elf-elf2hex --bit-width 512 --input hello.elf --output memory.txt

Recover the assembly

riscv64-unknown-elf-objdump -D hello.elf >FINAL.objdump -f

Compile step by step

This is a more detailed version of the riscv64-unknown-elf-gcc command. We can compile each file and then link them all together.

Assembly code

riscv64-unknown-elf-as -march=rv32im -mabi=ilp32  bootstrap.s -o bootstrap.o

C code

riscv64-unknown-elf-gcc -march=rv32im -mabi=ilp32  -c notmain.c -O2 -o notmain.o

Link

riscv64-unknown-elf-ld -T lscript -m elf32lriscv bootstrap.o notmain.o -o hello.elf

Notes

Median example operates on a matlab generated image stored after the 3d line of the memory. The image is also included separately at image.txt.