Re: after trivial update, 15.0 ARM64 system no longer boots

Lexi Winter:
> i am not really an expert on either ARM64 in general or on the RPi
> hardware in particular.  could anyone suggest how i could debug this
> problem, e.g. to get more information about why the system won't finish
> booting?

i dug into this a bit more, and to answer my own question:

- the boot failure that prompted the question appears to be a bug
  related to mmc, i reported it as PR 277884 [0].

- part of the problem, that i realise i forgot to mention in my initial
  post, was that my USB keyboard wouldn't work, so i couldn't interrupt
  the loader to use boot -v / -s / etc. or to access kdb.  this turned
  out to be an issue with the keyboard itself - a different keyboard
  worked fine.  the keyboard *does* work fine in FreeBSD once it's
  booted, which is odd; it's some $5 Amazon special, so i assume it just
  implements USB badly.

- even with the working keyboard, ctrl+alt+esc doesn't seem to work to
  break into kdb when the problem occurs.  i'm not sure if i'm doing
  something wrong here or that key sequence doesn't work over USB, so i
  wanted to try it via a serial console instead, which led to...

- i played around with USB OTG a bit to see if i could get a serial
  console that way.  FreeBSD does support serial over the OTG port (via
  the USB-C 'power' connector) and it works as a terminal in /etc/ttys,
  but neither U-Boot nor FreeBSD seem to be able to use it as a system
  console, which is a bit disappointing.  it would be nice if there was
  a way to get this working, because a serial console over USB would be
  very handy for working with these devices.

- in the mean time, i ordered a DB-9 serial HAT that connects to the
  UART to debug this and future issues.  once that arrives i can
  hopefully get some more info on the original problem.

	regards, lexi.

[0] "RPi4: mmc broken with GENERIC-NODEBUG":
    https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=277884