Examples of bare metal RiscV programming with a softcore on a fpga

This is a work in progress. Next thing to implement is a HDMI controller for video output. Currently, output constant green background.

In summary, I use fusesoc wishbone bus generator and VexriscV wishbone ibus and dbus. But VexriscV wishbone dbus need a little modification to make it compatible with fusesoc wishbone bus implementation.

I have added support to modify .mif file from Tom Verbeure tutorial. No need to recompile hardware each time.

DDR3 with Intel IP work but implementation is not optimized. Write speed is ~12MiB/s. So no burstmode with burst size greater than one supported right now. Bandwidth between cpu and memory is limited by Wishbone Bus with no burst support. Theoretical write speed from cpu: 50MHz * 4 bytes /(2 cycles per write + 2 cycles to read instruction) ~= 50 MiB/s.

Long term goal is to use BrianHG DDR3 memory controller. It offer faster speed ddr3 at 2x400MHz, memory interface at 200 MHz vs Intel 2x300MHz and memory interface at 150 MHz.

Started to work on usb. When building hardware, the timing requirements are not met because of TUSB1210 hardware controller but other peripherals still works.

Package required

• python 3

sudo apt install python-is-python3

• python pip

 sudo apt install python3-pip

• pyyaml

  pip install pyyaml

• python-yaml

sudo apt-get install python-yaml

• fusesoc

pip install fusesoc

• quartus 20.1

At the end of .bashrc file add:

export QUARTUS_VERSION=20.1
export PATH="/home/__your_user_name__/intelFPGA_lite/$QUARTUS_VERSION/quartus/bin:$PATH"

• RiscV toolchain from source or get pre-build binary

To compile from source:

 git clone https://github.com/riscv/riscv-gnu-toolchain.git
 cd  riscv-gnu-toolchain
 ./configure --prefix=/opt/riscv --enable-multilib
 sudo make -j N

where N is the number of processors.

At the end of .bashrc file add

export PATH=/opt/riscv/bin:$PATH

• Recent version of verilator to be able to do simulation.

TODO: add instruction to build verilator from source

My FuseSoc workspace folder is ~/Documents/bin/fusesoc. Adapt to your own folder. Also adapt paths to quartus binary and riscv toolchain.

To be able to program Deca board

See usb blaster udev chapter 3.2.2. Installing on Red Hat Enterprise 5 and 6

execute

sudo nano /etc/udev/rules.d/51-usbblaster.rules

Copy inside that file

BUS=="usb", SYSFS{idVendor}=="09fb", SYSFS{idProduct}=="6010", 
MODE="0666"
BUS=="usb", SYSFS{idVendor}=="09fb", SYSFS{idProduct}=="6810", 
MODE="0666"

Getting project files

git clone https://github.com/infphyny/FpgaRiscV.git

Inside the cloned directory

 fusesoc library add fusesoc_cores https://github.com/fusesoc/fusesoc-cores
 fusesoc library add gpio https://github.com/infphyny/gpio
 fusesoc library add wb_avalon_bridge https://github.com/infphyny/wb_avalon_bridge

Check inside fusesoc_cores/wb_intercon directory. If version number is lower than 1.3, get latest version

fusesoc library add wb_intercon https://github.com/olofk/wb_intercon

Building and executing an example for DecaWishbone soc

cd sw/Deca/DecaWishbone/accelerometer

1. Compile software that generate .hex and .mif files

make

2. Generate bitstream (.sof file) and upload ~ 5 min.

make hw

Note that make hw need to be done only once except if hardware source code is modified.

3. To update bram of the bitstream with new binary

make update_ram

4. To upload the previously generated bitstream:

make upload

5. To do a simulation:

make sim

Then ctrl-c after few seconds because .vcd file grow fast ~1 GiB/5s

6. To view assembly generated by riscv toolchain

make objdump

Terminal output

To view serial output from the soc execute the following program

picocom /dev/ttyUSBX --baud 115200 --imap lfcrlf 

where X is usb port number or use Arduino IDE serial monitor.

• Pinout

  

Deca RiscV soc properties

• VexRiscv cpu that implement RiscV 32 imc instructions set with a Wishbone bus.
• Frequency: 50 MHz
• Ram: 128k
• KEY0 is wired to reset.
• Uart RX need to be connected or pull high, otherwise Uart tx will be halted (SpinalHDL Uart implementation feature).
• To modify frequency, go in rtl/Deca/pll, execute quartus then choose pll for MAX10 and overwrite pll.v
• If frequency is changed, modify the fixed frequency in WbUart.scala and regenerate the WishboneUartCtrl.v to keep 115200 baud rate.
• To modify the ram size: Modify RAM_SIZE in Makefiles. Adjust gp and sp in crt0.S. Modify mem size parameter of Wishbone generator (wb_intercon) in Deca.core.

TODO

• Add code to clear bss memory section in startup code before main is called.
• Add documentation on how to generate the VexRiscv.v file from Vexriscv github repository.
• Show .vcd file location that generated from simulation.

List of hardware library

• VexRiscV cpu
• Hardware libraries provided by fusesoc

Documentation

• How to generate a linker script and https://twilco.github.io/riscv-from-scratch/2019/04/27/riscv-from-scratch-2.html.

• How to update bram from a previously generated bitstream: https://tomverbeure.github.io/2021/04/25/Intel-FPGA-RAM-Bitstream-Patching.html and https://github.com/tomverbeure/fpga_quick_ram_update

• Tom Verbeure ulpi hardware source code