Foboot: The Bootloader for Fomu

Foboot is a failsafe bootloader for Fomu. It exposes a DFU interface to the host. Foboot comes in two halves: A Software half and a Hardware half. These two halves are integrated into a single "bitstream" that is directly loaded onto an ICE40UP5k board, such as Fomu.

Requirements

To build the hardware, you need:

• Python 3.5+
• Nextpnr
• Icestorm
• Yosys
• Git

Subproject hardware dependencies will be taken care of with lxbuildenv.

To build the software, you need:

• RISC-V toolchain

Building the project

The hardware half will take care of building the software half, if it is run with --boot-source bios (which is the default). Therefore, to build Foboot, enter the hw/ directory and run:

$ python3 foboot-bitstream.py --revision hacker --seed 19

This will verify you have the correct dependencies installed, compile the Foboot software, then synthesize the Foboot bitstream. The resulting output will be in build/gateware/. You should write build/gateware/top-multiboot.bin to your Fomu device in order to get basic bootloader support.

The seed argument is to set initial conditions for the place-and-route phase. nextpnr-ice40 uses a simulated annealing algorithm that can result in one of several locally optimal layouts. Only some of these will meet the timing requirements for Fomu.

If you see something like

ERROR: Max frequency for clock 'clk48_$glb_clk': 45.41 MHz (FAIL at 48.00 MHz)

try a different seed. You can search for an appropriate seed with:

for seed in $(seq 0 100)
do
  python3 ./foboot-bitstream.py --revision pvt --seed $seed 2>&1 |
     grep 'FAIL at 48.00 MHz' && continue
  echo "Working Seed is $seed"
  break
done

This can take a considerable time.

Usage

You can write the bitstream to your SPI flash.

Loading using fomu-flash

If you're using fomu-flash, you would run the following:

$ fomu-flash -w build/gateware/top-multiboot.bin
Erasing @ 018000 / 01973a  Done
Programming @ 01973a / 01973a  Done
$ fomu-flash -r
resetting fpga
$

Fomu should now show up when you connect it to your machine:

[172294.296354] usb 1-1.3: new full-speed USB device number 33 using dwc_otg
[172294.445661] usb 1-1.3: New USB device found, idVendor=1209, idProduct=70b1
[172294.445675] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[172294.445684] usb 1-1.3: Product: Fomu Bootloader (0)
[172294.445692] usb 1-1.3: Manufacturer: Kosagi

Using dfu-util to flash the bootloader

First build the flasher program, that will run on the Fomu:

cd booster
cc -O2 -o make-booster -I ./include make-booster.c

Then package that up ready for loading:

cd releases
bash ./release.sh pvt

This will create a new directory in releases named by the head of your git tree and the last official release. So you'll see something like v2.0.3-8-g485d232

In that directory will be a file named pvt-updater-version.dfu Load and exectue it using dfu-util:

dfu-util -D pvt-updater-v2.0.3-8-g485d232.dfu

Your Fomu will flash rainbow for about five seconds, then reboot and go back to blinking steadily. To verify that your code has loaded, use

dfu-util -l

and look at the version output.

Loading and running other bitstreams

To load a new bitstream, use the dfu-util -D command. For example:

$ dfu-util -D blink.bin

This will reflash the SPI beginning at offset 262144.

To exit DFU and run the bitstream at offset 262144, run:

$ dfu-util -e

Note that, like Toboot, the program will auto-boot once it has finished loading.

Building the Software

Software is contained in the sw/ directory.