README: Add Linux on Microwatt instructions

These instructions are similar to those at

except they describe how to build the artifacts from scratch instead of
downloading them.

Signed-off-by: Joel Stanley <>
Joel Stanley 1 year ago
parent a31725d989
commit 9ec22af256

@ -122,6 +122,68 @@ You should then be able to see output via the serial port of the board (/dev/tty
fusesoc run --target=nexys_video microwatt

## Linux on Microwatt

Mainline Linux supports Microwatt as of v5.14. The Arty A7 is the best tested
platform, but it's also been tested on the OrangeCrab and ButterStick.

1. Use buildroot to create a userspace

A small change is required to glibc in order to support the VMX/AltiVec-less
Microwatt, as float128 support is mandiatory and for this in GCC requires
VSX/AltiVec. This change is included in Joel's buildroot fork, along with a
git clone -b microwatt
cd buildroot
make ppc64le_microwatt_defconfig

The output is `output/images/rootfs.cpio`.

2. Build the Linux kernel
git clone
cd linux
make ARCH=powerpc microwatt_defconfig
make ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- \
CONFIG_INITRAMFS_SOURCE=/buildroot/output/images/rootfs.cpio -j`nproc`

The output is `arch/powerpc/boot/dtbImage.microwatt.elf`.

3. Build gateware using FuseSoC

First configure FuseSoC as above.
fusesoc run --build --target=arty_a7-100 microwatt --no_bram --memory_size=0

The output is `build/microwatt_0/arty_a7-100-vivado/microwatt_0.bit`.

4. Program the flash

This operation will overwrite the contents of your flash.

For the Arty A7 A100, set `FLASH_ADDRESS` to `0x400000` and pass `-f a100`.

For the Arty A7 A35, set `FLASH_ADDRESS` to `0x300000` and pass `-f a35`.
microwatt/openocd/flash-arty -f a100 build/microwatt_0/arty_a7-100-vivado/microwatt_0.bit
microwatt/openocd/flash-arty -f a100 dtbImage.microwatt.elf -t bin -a $FLASH_ADDRESS

5. Connect to the second USB TTY device exposed by the FPGA

minicom -D /dev/ttyUSB1

The gateware has firmware that will look at `FLASH_ADDRESS` and attempt to
parse an ELF there, loading it to the address specified in the ELF header
and jumping to it.

## Testing

- A simple test suite containing random execution test cases and a couple of