docs: provide instructions for flashing with OpenOCD / BMDA; provide instructions for non-autodetect TTYs

[jwise]

For those of us without J-Links, and on Macs where the ancient version of PyFtdi misbehaves, we provide instructions for using OpenOCD (or BMDA) as a flash tool.

[gmarull]

Since OpenOCD seems to be supported as a core feature, this should be integrated with ./waf flash (waftools/openocd.py, main wscript). Flashing definitely needs some love to be multirunner capable (as there are better options than OpenOCD nowadays), similar to Zephyr.

Just tested this locally and it works without invoking any GDB:

# myconfig.cfg
set WORKAREASIZE 0x4000
source [find interface/jlink.cfg]
transport select swd
source [find target/nrf52.cfg]

openocd -f myconfig.cfg -c "init;targets;reset init;flash write_image erase my.hex;reset run;shutdown"

[gmarull]

OpenOCD alone can take care of flashing, reset, etc. Adding gdb seems unnecessary.

[jwise]

I think I want to wait to integrate with ./waf flash until we have a bootloader -- we could make waf flash flash it on nRF52 for now, but it seems reasonable that it's a fairly manual process at the moment.

I guess you could do this without gdb. But basically any time you flash the system at this point you want to do it with a debugger connected :)

Should we merge this for now, and then revisit later once asterix stabilizes?

[gmarull]

I think I want to wait to integrate with ./waf flash until we have a bootloader -- we could make waf flash flash it on nRF52 for now, but it seems reasonable that it's a fairly manual process at the moment.

I guess you could do this without gdb. But basically any time you flash the system at this point you want to do it with a debugger connected :)

Should we merge this for now, and then revisit later once asterix stabilizes?

I prefer to keep gdb out of the game as it's not strictly required. It can be manual, but just with openocd, see my snippet above.

[gmarull]

@jwise ./waf flash_fw should work out of the box now, so this PR can be closed.