This makes rtt output work right when using `cargo run` in release mode.
Debug was already enabled for release builds in some of the examples but
not all.
Make sure that the ptr() function for ROM functions always returns
the actual ROM pointer. This allows the use of flash I/O while the
function cache is enabled.
This provides a helper function with an async implementation, that
will only return (or error) when it was able to read that many bytes,
sleeping until ready.
Additionally, corrected the documentation for Ringbuffer functions to use
"elements" instead of "bytes" as the types were already generic over the
word/element size.
The DAC driver defaults to enabling the channel trigger, but leaves it
at the default value of TIM6 TRGO, then performs a software trigger
after writing the new output value. We could change the trigger
selection to software trigger, but for this example it's simpler to just
disable the trigger.
using these will require some linker script intervention. setting the
core0 stack needs linker intervention anyway (to provide _stack_start),
having it also provide _stack_end for the guard to use is not that much
of a stretch.
the region field of the register is four bits wide followed by the valid
bit that causes the rnr update we rely on for the rasr write. 0x08 is
just a bit short to reach the valid bit, and since rp2040 has only 8
regions it (at best) doesn't do anything at all.
the adc constantly pulls a small but significant amount of current while
the hardware is enabled. this can have quite an effect on sleeping
devices that also use the adc.
