Get riscv-32 musl toolchain. Get u-boot tree with usb support and compile it.
#toolchain
wget https://musl.cc/riscv32-linux-musl-cross.tgz
tar xf riscv32-linux-musl-cross.tgz
export PATH=$PWD/riscv32-linux-musl-cross/bin:$PATH
#u-boot
git clone https://github.com/madushan1000/u-boot -b bl808/usb-udc
cd u-boot
#compile
make CROSS_COMPILE=riscv32-linux-musl- ox64_m0_defconfig
make CROSS_COMPILE=riscv32-linux-musl-
Put bl808 into flash mode and flash u-boot(this is only needed the first time until we have u-boot on the board)
#install the flash tool
pip3 install bflb-mcu-tool
#flash u-boot, replace /dev/ttyACM0 with your uart port
bflb-mcu-tool --chipname bl808 --port /dev/ttyACM0 --baudrate 115200 --firmware uboot.bin
Reset the board, now there should be a usb device that shows up as a fastboot device.
❯ fastboot devices
???????????? Android Fastboot
Board will power up and listen as a fastboot device forever by default. We can run fastboot commands to configure the board.
❯ fastboot getvar version
version: 0.4
Finished. Total time: 0.000s
❯ fastboot oem run:'ls mmc 0'
OKAY [ 0.445s]
Finished. Total time: 0.445s
But the fastboot protocol implimented by u-boot is not fully compatible with android fastboot, so we need to use uuu(https://github.com/nxp-imx/mfgtools)
# install uuu
$ sudo apt install uuu
$ uuu -s
# uuu console
U>CFG: FB: -vid 0x18d1 -pid 0x4e40
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
Okay
U>FB: reboot
>Start Cmd:FB: reboot
New USB Device Attached at 3:9
3:9>Okay (0s)
Okay
U>
we can also use uuu scripts
$ uuu -V -b reboot.lst
Wait for Known USB Device Appear...
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
>Okay (0s)
New USB Device Attached at 3:9
3:9>Start Cmd:FB: reboot
3:9>Okay (0.001s)
3:9>Start Cmd:FB: Done
3:9>Okay (0s)
Get the D0 u-boot firmware from here (https://github.com/openbouffalo/u-boot/releases/tag/bl808-2023-02-19)
$ wget https://github.com/openbouffalo/u-boot/releases/download/bl808-2023-02-19/fw_payload-bl808-2023-02-19.elf
$ uuu -V -b boot-d0.lst
Wait for Known USB Device Appear...
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
>Okay (0s)
New USB Device Attached at 3:9
3:9>Start Cmd:FB: getvar version
0.43:9>Okay (0.001s)
3:9>Start Cmd:FB: ucmd setenv fastboot_buffer 0x51000000
3:9>Okay (0s)
3:9>Start Cmd:FB: download -f fw_payload-bl808-2023-02-19.elf
3:9>Okay (0.175s)
3:9>Start Cmd:FB: ucmd rproc init 0 || true
3:9>Okay (0.024s)
3:9>Start Cmd:FB: ucmd rproc load 0 51000000 1000000
3:9>Okay (0.044s)
3:9>Start Cmd:FB: ucmd rproc start 0
3:9>Okay (0s)
3:9>Start Cmd:FB: Done
3:9>Okay (0s)
We can flash stuff to sdcard using uuu. For flashing the sdcard, it has to be patitioned. Then we can create a raw partition image and flash it over USB.
If the first parition of the sdcard is 200Mb.
$ truncate -s $((200*1024*1024)) disk.raw
$ mkfs.ext4 disk.raw
$ mkdir mnt
$ mount disk.raw mnt
$ echo 'test' > mnt/test
$ umount mnt
$ uuu -V -b flash-sdcard.lst
Wait for Known USB Device Appear...
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
>Okay (0s)
New USB Device Attached at 3:9
3:9>Start Cmd:FB: flash -raw2sparse 0 disk.raw
100%3:9>Okay (43.77s)
3:9>Start Cmd:FB: Done
3:9>Okay (0s)
Flashing to internal flash is also possible, be careful not to overwrite u-boot.
$ uuu -V -b flash-internal-flash.lst
Wait for Known USB Device Appear...
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
>Okay (0s)
New USB Device Attached at 3:9
3:9>Start Cmd:FB: getvar version
0.43:9>Okay (0s)
3:9>Start Cmd:FB: download -f bl_mcu_sdk/examples/helloworld/build/build_out/helloworld_bl808_m0.bin
3:9>Okay (0.007s)
3:9>Start Cmd:FB: ucmd sf probe
3:9>Okay (0.008s)
3:9>Start Cmd:FB[-t 60000]: ucmd sf update 0x51000000 0x300000 0x100000
3:9>Okay (9.664s)
3:9>Start Cmd:FB: reboot
3:9>Okay (0s)
3:9>Start Cmd:FB: Done
3:9>Okay (0s)
It's possible for u-boot to boot the above flashed firmware using some magic to map 0x300000 as XIP start address
$ uuu -V -b boot-firmware.lst
Wait for Known USB Device Appear...
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
>Okay (0s)
New USB Device Attached at 3:9
3:9>Start Cmd:FB: getvar version
0.43:9>Okay (0s)
3:9>Start Cmd:FB: ucmd mw 0x2000b0A0 0x300000
3:9>Okay (0s)
3:9>Start Cmd:FB: ucmd dcache flush
3:9>Okay (0.001s)
3:9>Start Cmd:FB: acmd go 0x58000000
3:9>Okay (0s)
3:9>Start Cmd:FB: Done
3:9>Okay (0s)
We can also update u-boot to a newer verison over usb. To do that, we need to generate a proper bootheader for u-boot using bflb-mcu-tool
bflb-mcu-tool --chipname bl808 --build --firmware uboot.bin
the completed image will end up on bflb-mcu-tool python package directory(ex: ~/.local/lib/python3.10/site-packages/bflb_mcu_tool/chips/bl808/img_create_mcu/whole_img.bin) copy it to the working dir and,
$ uuu -V -b update-u-boot.lst
Wait for Known USB Device Appear...
>Start Cmd:CFG: FB: -vid 0x18d1 -pid 0x4e40
>Okay (0s)
New USB Device Attached at 3:9
3:9>Start Cmd:FB: getvar version
0.43:9>Okay (0s)
3:9>Start Cmd:FB: download -f whole_img.bin
3:9>Okay (0.032s)
3:9>Start Cmd:FB: ucmd sf probe
3:9>Okay (0.007s)
3:9>Start Cmd:FB[-t 60000]: ucmd sf update 0x51000000 0 0x100000
3:9>Okay (7.227s)
3:9>Start Cmd:FB: reboot
3:9>Okay (0s)
3:9>Start Cmd:FB: Done
3:9>Okay (0s)
If u-boot update goes wrong, we will have to flash u-boot again using the bl808 flash mode.