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LiteX

FemtoRV can be used with LiteX.

LiteX is an easy-to-use framework for creating SoCs.

  • it supports many different FPGA boards
  • it includes gateware for many different devices (SDRAM, HDMI, SDCard, SATA ...)
  • it has basic software support (a BIOS)
  • with some cores (VexRiscV) it can even run Linux (not possible with FemtoRV though)

The remainder of this file contains the instruction to install LiteX and its dependencies.

Install open-source FPGA development toolchain

Before starting, you will need to install the open-source FPGA development toolchain (Yosys, NextPNR etc...), instructions to do so are given here.

Install LiteX

Follow setup instructions from LiteX website

TL;DR

$ mkdir LiteX
$ cd LiteX
$ wget https://raw.githubusercontent.com/enjoy-digital/litex/master/litex_setup.py
$ chmod +x litex_setup.py
$ ./litex_setup.py --init --install --user 
$ pip3 install meson ninja
$ sudo ./litex_setup.py --gcc=riscv

Synthesize

Instructions to synthesize are different, depending on the board you have.

Connect to the SoC

Start a terminal emulator. You can use the one bundled with LiteX (lxterm). You will need to determine on which port it is plugged (one of /dev/ttyUSBnnn), use $dmesg right after plugging it (or try different values). Supposing it is ttyUSB0, do:

  $litex_term /dev/ttyUSB0

Then press <enter>. You will see the litex> prompt.

  • As you may have guessed, do litex> help to see the possible commands.
  • Try litex> sdram_test. If everything went well, it should say Memtest OK.
  • To exit, press <ctrl><\>

FemtoRV variants

LiteX can use all the variants of FemtoRV, from the tiniest: femtorv-quark (RV32I) to the bigest one with an FPU: femtorv-petitbateau (RV32IMFC+irq).

variant instruction set
quark RV32I
electron RV32IM
intermissum RV32IM+irq
gracilis RV32IMC+irq
petitbateau RV32IMFC+irq 
$ python3 -m litex_boards.targets.radiona_ulx3s --cpu-type=femtorv --cpu-variant=petitbateau --build --load --device LFE5U-85F --sdram-module AS4C32M16

Software

Time to compile and install software on your SoC.

Compiling RiscV software for the device

See LiteX demo here

$ cd <LiteX installation directory>
$ litex_bare_metal_demo --build-path build/radiona_ulx3s/

Sending software to the device

lxterm can be used to send a binary to the device, as follows:

$lxterm --kernel <software.bin> --speed 115200 /dev/ttyUSB0

Notes - LiteX cheatcodes and files

If you want to learn more about how LiteX works, reading the sourcecode is a good idea ! Some important links and files:

  • simulation: litex_sim --cpu-type=femtorv --with-sdram
  • ULX3S pins: litex-boards/litex_boards/platforms/radiona_ulx3s.py
  • ULX3S: litex-boards/litex_boards/targets/radiona_ulx3s.py
  • femtorv: litex/litex/soc/cores/cpu/femtorv/core.py
  • bios: litex/litex/soc/software/bios/main.c
  • framebuffer: litex/litex/soc/cores/video.py
  • wishbone-utils