[9front] Getting Started with Kernel Development?

["chötrin." <chotrin@posteo.net>]

Hi y'all!

I'm running 9front on a RPi 3B+, and it looks like there's no audio
device support here.  I think I'd like to try my hand at implementing
that, but hacking at the Plan 9 kernel is new to me.

uramekus pointed me to nemo's "Notes on the Plan 9 3rd edition Kernel
Source," which I'm currently perusing to try to grok what's going on.
It's been really helpful so far.

I've also got the "BCM2835 ARM Peripherals" spec, which specifies how
to interact with the chip's I2S audio interface.

I *think*, at least upon cursory inspection, I'm going to be
implementing the bcm64 end of /sys/src/9/port/audioif.h to speak with
/sys/src/9/port/devaudio.c.  I can use the /sys/src/9/pc tree as an
example to follow, assuming I can figure out how the boot code is
calling, say, audiosb16link().  I have plenty of homework ahead of me,
to say the least.

My question to you is this: where do I get started actually making
changes to the 9front kernel and testing them out?  What does, or
should, the development flow look like for me?  Ideally, I'd be able
to go back and forth between a known good kernel and whatever I'm
hacking at.  I don't want to be backing up my SD card and restoring it
over and over again, if at all possible.

If there's some handy writeups, documentation, or tips y'all have for
getting started with this, I'd be much obliged!

Thanks for reading, and be well. :)

chötrin.