How to build and use OpenSBI on spike, qemu and Shakti SoC?

OpenSBI (Open Supervisor Binary Interface) is a RISC-V specific runtime service provider. The goal of the OpenSBI project is to provide an open-source reference implementation of the RISC-V SBI specifications for platform-specific firmwares executing in M-mode.

The RISC-V Supervisor Binary Interface (SBI) is the recommended interface between:

1. A platform-specific firmware running in M-mode and a bootloader, a hypervisor, or a general-purpose OS executing in S-mode or HS-mode.
2. A hypervisor running in HS-mode and a bootloader or a general-purpose OS executing in VS-mode.

In this article, we are going to see how to build OpenSBI on SPIKE, QEMU and SHAKTI SoC.

Requirements,

• Spike simulator
• QEMU emulator
• Arty A7 Board with SHAKTI SoC (VAJRA) Programmed.

Step 1: Building OpenSBI

git clone https://github.com/riscv/opensbi.git
cd opensbi
export CROSS_COMPILE=riscv64-unknown-linux-gnu-

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Step 2: OpenSBI on SPIKE

The Spike is a RISC-V ISA simulator which implements a functional model of one or more RISC-V harts.

Note: shakti-tools can be installed as spike is a part of it.

2.1 Check if SPIKE is successfully installed

username@Riselab:~$ which spike
/home/username/shakti-tools/riscv64/bin/spike

2.1 Building the payload

make PLATFORM=generic

2.2 Running the test payload

spike build/platform/generic/firmware/fw_payload.elf

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Step 3: OpenSBI on QEMU

3.1 Building QEMU for SHAKTI

git clone https://gitlab.com/shaktiproject/software/qemu.git
cd qemu
git checkout shakti/c-class
mkdir build
cd build
../configure --target-list="riscv32-softmmu riscv64-softmmu"
make

Then add this line to bashrc,

 export PATH=$PATH:<path/to/qemu>/build

For instance: export PATH=$PATH:/home/username/qemu/build

3.2 Check if the installation is successful

qemu-system-riscv64 -M help

This command displays the available machines that qemu can simulate, shakti_c is what we require.

3.3 Building the payload for QEMU

cd opensbi
wget -c https://gitlab.com/behindbytes/shakti-binaries/-/raw/master/dts/shakti.dtb
export CROSS_COMPILE=riscv64-unknown-elf-
export FW_FDT_PATH=./shakti.dtb
make PLATFORM=generic

3.4 Running the test payload

qemu-system-riscv64 -M shakti_c -nographic -bios path/to/fw_payload.elf

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Step 4: OpenSBI on SHAKTI SoC (Vajra)

4.1 Building SHAKTI OpenSBI

Firstly, we need to clone the shakti-opensbi repository and build the test payload.

git clone https://gitlab.com/shaktiproject/software/shakti-opensbi.git
cd opensbi
wget -c https://gitlab.com/behindbytes/shakti-binaries/-/raw/master/dts/shakti.dtb
export CROSS_COMPILE=riscv64-unknown-elf-
make PLATFORM=generic FW_FDT_PATH=./shakti.dtb

4.2 Running the test payload on SHAKTI-SOC

Now, open three terminals, one for each of the following,

Terminal 1: Firstly Connect to serial output by using miniterm or gtkterm with the baud rate of 115200

For instance,

$ sudo miniterm.py /dev/ttyUSB1 115200

Note:

• “/dev/ttyUSB1” – ttyUSB means “USB serial port adapter”
• The “1” (“0” or “1” or “2”“here means the USB device number on your system. The FPGA board is connected to that USB device number.

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Terminal 2: After that, Connect to the FPGA board by using the OpenOCD provided by shakti-tools and its respective configuration file.  (Read how OpenOCD and RISC-V GDB work together to establish a connection between our PC and the Microprocessor)

For instance,

$ cd shakti-sdk
$ cd ./bsp/third_party/vajra
$ sudo $(which openocd) -f ftdi.cfg

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Terminal 3: Now, open RISC-V GDB riscv64-unknown-elf-gdb from shakti-tools.

The output executable is created in <path-to-shakti-opensbi>/build/platform/generic/firmware/ as fw_payload.elf. Load up the .elf file by following the below steps,

$ riscv32-unknown-elf-gdb

source gdb.script
file ~/Documents/shakti-opensbi/build/platform/generic/firmware/fw_payload.elf
load
c