This document is part of the hoverboard firmware documentation.
This document describes how to flash the firmware directly with Raspberry PI Zero.
The hoverboard circuit board has the SWD (single wire debug) pins as a debug points next to the processor. You can see the pins in the following picture.
I've marked the pins with colors corresponding the pin function, from top to bottom:
+3.3V, SWCLK, GND, SWDIO. The +3.3V should not be used, as it flows backwards
through the power supply regulators and most likely breaks them! Use the main power supply
(or charger?) when flashing.
In addition to the 3 necessary SWD pins (clock, data and ground) there is another pin that
can/should be used: the reset pin. It has no test point but the connection can be found
from the left side of the processor. NRST is on the right side of C4 and on the left
side of R19.
The reset pin might not be necessary, but my experience is that without using it during flashing/debugging, the processor might start up from wrong memory address which causes huge amount of unnecessary pain. I rather use the reset pin and know the state of the processor after flashing.
The same pins on the Raspberry PI zero are according to following image. These are not the default pins, but I ended up using these wafter trying a "native" interface which I could not get to work. I didn't change the wiring, I rather modified the "sysfsgpio" config that I got to work.
Basically just connect all the similarly named pins together. But do not connect the +3.3V!
OpenOCD is used for flashing. However, the stock OpenOCD on my Raspbian
did not have the sysfsgio interface built in, so I had to rebuild OpenOCD from source, using
--enable-sysfsgpio configure flag.
After that, copy the sysfsgpio-raspberrypi.cfg to
the interface folder of OpenOCD, in my system that was /usr/local/share/openocd/scripts/interface/.
Then, have the openocd.cfg in the same directory where you're going
to run OpenOCD, and also have the firmware hover.bin in the same directory.
Launch OpenOCD by running
sudo openocd
It should find the processor and halt it.
Then you need to open telnet to interface with it:
telnet localhost 4444
in that you can enter commands. To unlock the chip on first flashing, enter
stm32f1x unlock 0
reset halt
then you can flash the firmware with
flash write_image erase build/hover.bin 0x8000000
reset
If you run just reset the board should start. You can also run reset halt to halt it.
If OpenOCD was running between flashings, run reset halt always before flashing. Also remember
to keep the power button pressed, or use a jumper on the connector. Otherwise the processor may
release the power supply during reset and/or flashing and everything will fail.
There is some more documentation on the main readme on how to unlock the chip and so on. Those commands are run directly from OpenOCD command line, but I never got that to work, so I did this with telnet.
Copyright (C) 2019 Lauri Peltonen