There was a very subtle bug in the ADC read code: it stores a pointer to
a variable in a register, waits for the hardware to complete the read,
and then reads the value again from the local variable. Unfortunately,
the compiler doesn't know there is some form of synchronization
happening in between.
This can be fixed in roughly two ways:
* Introduce some sort of synchronization.
* Do a volatile read from the variable.
I chose the second one as it is probably the least intrusive. We
certainly don't need atomic instructions (the chip is single threaded),
we just need to tell the compiler the value could have changed by making
the read volatile.
Go 1.19 started reformatting code in a way that makes it more obvious
how it will be rendered on pkg.go.dev. It gets it almost right, but not
entirely. Therefore, I had to modify some of the comments so that they
are formatted correctly.
Do it all at once in preparation for Go 1.18 support.
To make this commit, I've simply modified the `fmt-check` Makefile
target to rewrite files instead of listing the differences. So this is a
fully mechanical change, it should not have introduced any errors.
This commit refactors PWM support in the machine package to be more
flexible. The new API can be used to produce tones at a specific
frequency and control servos in a portable way, by abstracting over
counter widths and prescalers.
This newer peripheral supports DMA (through EasyDMA) and should
generally be faster. Importantly for some operations: interrupts (within
255 byte buffers) will not interfere with the SPI transfer.
The nrf52 series is all very similar and copying the code only makes it
harder to maintain the code or to add more chips in the nrf52 series
(for example, the nrf52833 as used in the micro:bit v2).
This commit also has a small improvement regarding pins: it now includes
chip-level pin names (P0.00, P0.01, etc) to the machine package.
