- updates enables or disables updates in the loader
- verilator-only will turn off routines that access hardware not
present in verilator (e.g. leads to a bus lockup)
- simulation-only turns of features that take a long amount of time
and aren't necessary in simulation, such as bulk clearing of
all RAM - in simulation, we can configure the simulator to do this
for us prior to boot; but in HW, of course, RAM is just random,
or worse, has the previous session's secrets in it.
cramium-soc is moving closer to the platonic SoC specifier,
and the board-* features are for the specific boards that use
cramium-soc
This division of feature flags feels a lot nicer and cleaner -
if it holds up to further development, I think this style might
become the new standard for Xous (as opposed to a single level
of feature flag where both SoC and board target are conflated in
terms of meaning - which kind of made sense when the CPU was
an FPGA and could actually have different features for different
boards, but for ASICs this wouldn't happen).
I felt uncomfortable leaving the oscillator setting entirely
outside the PLL routine, so as a compromise I defer the oscillator
switch-over until after the initial PLL settings are loaded.
This makes both the simulation model and the actual hardware
happy. I think probably what the simulation model *should* have
done is consider the "powerdown" pin when checking the validity
of the signals going into the PLL model - but this is impossible
to modify/check because the PLL is provided as an encrypted blob :(
this transition was in the reference C code, but in verilog simulation
it turns out it activates the PLL in an invalid mode which can lead
to glitching. Removing this makes both the simulation happy and
presumably the PLL happier as well.
this doesn't protect against malicious tampering (because
the public key is the developer key) but it will at least
catch correctness errors in USB upload and filesystem
behavior.
we can now recover from an I2C timeout and get the PMIC data
out, but mysteriously, when we leave the routine, the CPU hangs.
I think fundamentally the I2C instability is due to something
very wonky inside the chip itself, so the recovery only papers
over an issue that is only fixed with a reboot...
