Signaloid C0-microSD Litex Integration

This is an example RISC-V SoC implementation on the Signaloid C0-microSD FPGA that can run C/C++ software.
This project offers Makefiles to build and flash the FPGA bitstream, and the firmware binary.

Gateware

This example utilizes the default Signaloid C0-microSD target design from litex-boards. It consists of:

• VexRISC-V-Lite SoC, with IM support.
• UART interface for serial communication support.
• 12MHz default system clock.
• 128kiB SRAM.
• 14MiB binary & files storage on SPI Flash.

Firmware

The firmware implements a "blink" example, with UART serial communication support.

• Blinking the Signaloid C0-microSD on-board red and green LEDs every 250ms.
• Printing the turned-on LED.
• Echoing the UART tx bytes on rx.

Getting Started

Note

This repository assumes that you have already installed the following tools.

• Yosys
• nextpnr
• IceStorm
• RISC-V GNU Toolchain for RV32IM ISA extension

We recommend using the OSS CAD Suite to install Yosys, nextpnr, and IceStorm.

Clone this repository

To clone this repository recursively, run the following command:

git clone --recursive git@github.com:signaloid/C0-microSD-litex-integration

If you forgot to clone with --recursive and end up with empty submodule directories, you can remedy this with:

git submodule update --init --recursive

You can update all submodules with the following commands:

git pull --recurse-submodules
git submodule update --remote --recursive

Prepare virtual environment

Run the environment preparation make command, on the project's root directory:

make prep

Build and flash both gateware and firmware

Before running this, make sure that the CROSS_COMPILE_PATH variable is properly set in the config.mk file with the installation path of the RISC-V GNU Toolchain for RV32IM ISA extension. Its default value is set to opt/riscv32im/bin. Also, make sure that the DEVICE variable in the config.mk file is set to the correct device path (follow the Identify the Signaloid C0-microSD guide). Run this in the project's root directory:

make flash

Structure

This repository consists of several subdirectories.

• gateware/: LiteX SoC design.
• firmware/: C based code example.
• build/: Litex generated directory after the building process. Contains the FPGA design bitstream, the Litex generated C libraries, the compiled firmware binary, and the Litex autogenerated documentation.
• submodules/: Dependencies on tools outside this repository.
  • C0-microSD-utilities: C0-microSD-toolkit for flashing purposes.

Makefiles

This repository contains two Makefiles, one for the gateware, the main Makefile, and one for the firmware, the firmware/Makefile. The firmware Makefile targets are also accessible from the main Makefile, so you can run its commands from both the firmware/ and the project's root directory. For details on the firmware Makefile, see the firmware/README.md file.

You should run the following commands from the project's root directory, where the main Makefile is located.

Build both gateware and firmware

To build both gateware and firmware run:

make

This command:

1. Prepares the environment for development, if haven't already.
2. Builds the Litex gateware, and software libraries.
3. Proceeds with synthesize, place 'n' route, and pack.
4. Builds the Litex autogenerated SoC documentation, in the build/signaloid_c0_microsd/docs/html/ directory.
5. Builds the C firmware.

Flash both gateware and firmware

To flash both gateware and firmware run:

make flash

Clean all build files

To delete all generated files except the virtual environment run:

make clean

Clean all virtual environment files

make clean-env

Prepare the environment for development

To prepare the environment run:

make prep

This command:

1. Downloads all git submodules in the submodules directory.
2. Creates a python virtual environment at .venv.
3. Installs all python required packages defined on the requirements.txt file using pip.

Build the gateware

To build the SoC bitstream run:

make gateware

Flash the gateware

To flash the SoC bitstream to the Signaloid C0-microSD run:

make flash-gateware

Test the gateware target script for verilog compilation errors

This is useful for debugging the target script. To test for verilog compilation errors run:

make test-target

Build the C firmware

To build the SoC firmware run:

make firmware

Flash the firmware

To flash the SoC firmware to the Signaloid C0-microSD run:

make flash-firmware

Clean the firmware build files

To clean the SoC firmware build files run:

make clean-firmware

Print the firmware Makefile variables

To print all the variables of the firmware Makefile run:

make print-vars-firmware

Print the main Makefile variables

To print all the variables of the main Makefile run:

make print-vars

Gateware Bitstream

The gateware bitstream is stored in the build/signaloid_c0_microsd/gateware/ directory with the name signaloid_c0_microsd.bin.

Firmware Binary

The firmware binary is stored in the build/signaloid_c0_microsd/software/ directory with the name signaloid_c0_microsd_firmware.bin.