How to use PicoRV CPU on BeagleV-Fire#
Introduction#
The PicoRV is a 32-bit RISC-V CPU subsystem on BeagleV-Fire’s FPGA fabric, functionally equivalent to the PRU subsystem on BeagleBone Black. The core is designed for low-latency I/O operations and offloading smaller tasks like PWM, LEDS, etc.
Prerequisites#
To be able to program PicoRV, you’ll need to have following packages installed on your host computer:
gcc-riscv64-unknown-elf
picolibc-riscv64-unknown-elf
These packages are used for compiling the code for the PicoRV.
For debian-based systems like ubuntu, you can use following commands:
sudo apt install gcc-riscv64-unknown-elf picolibc-riscv64-unknown-elf
If you are using any other linux distro these packages can be downloaded from respective package managers. But, it is highly recommended to use docker for accurate results.
Once you have docker installed:
Start a container with ubuntu image.
Install the required toolchain using above mentioned command (remember not to use ‘sudo’ inside the docker container).
sudo docker run -it ubuntu:latest
After installing the necessary tools, you are all set.
How to use the CPU#
1. Boot the CPU with firmware#
Step 1#
Todo
Fix path!
Navigate to sources/FPGA-design/script_support/components/SOFTCORE/PICO_RISCV/firmware in the BeagleV-Fire repository.
Step 2#
Edit the firmware.c file by adding your code in the main function. You can create your own custom file but remember to use firmware.h file for pre-defined functions to access gpios.
Step 3#
Now run the generatehex.sh to compile the code. (remember to edit the file name in the script of you are using custom file)
. ./generatehex.sh
If you are using docker clone the repository on your docker container or use docker copy, then compile the program and use docker copy to obtain the hex file.
To copy file from local system to docker container:
docker cp ./path/to/file CONTAINER:/path/to/directory
To copy file from docker container to local system:
docker cp CONTAINER:/path/to/file /path/to/directory
To check the name of docker ‘CONTAINER’:
docker ps -a
This will list all the running and stopped containers To restart a stopped container, use:
sudo docker start name_of_container -i
Step 4#
Select PicoRV build option for bitstream generation
Once the code is compiled, build the bitstream using the ‘build-bitstream.py’ script.
python build-bitstream.py ./build-options/picorv-softcore.yaml
Note
The Gitlab CI does not support the softcore code compilation yet, so the bitstream must be generated locally.
Step 5#
Program BeagleV-Fire with Your Custom Bitstream.
2. Programming the softcore in run-time#
Step 1#
Program the softcore with custom bitstream with picorv-softcore build-option.
Follow the steps mentioned in previous section.
Step 2#
Edit and compile your new code in your local machine.(BeagleV-Fire does not support on-board compilation for softcore programs yet, this feature will be added soon.)
Follow Steps 2 and 3 in previous section for compiling your new program.
Step 3#
Copy the firmware directory from BeagleV-Fire repository to your board.
sudo scp -r path/to/firmware beagle@192.168.7.2:/home/beagle
Step 4#
Overwriting PicoRVs program memory.
Compile the ‘AXI_test.c’ file using gcc and execute it.
gcc -o AXI_test AXI_test.c
sudo ./AXI_test
This will open a interactive menu with various options that you can try out and access the program memory of the PicoRV.
Here we will select option 2 to upload the hex file we just compiled to the CPU.
Note
This compilation in step 2 is to generate a hex file to program the Softcore, while the compilation in Step 3 is performed to command the Linux system on-board to access the program memory of the Softcore.
Note
The filename in AXI_test.c for the hex file is set as firmware.hex, so make sure the name of the hex file you compiled is the same else change the filename pointer in AXI_test.c.
