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 means that machine.UART0, machine.UART1, etc are of type
*machine.UART, not machine.UART. This makes them easier to pass around
and avoids surprises when they are passed around by value while they
should be passed around by reference.
There is a small code size impact in some cases, but it is relatively
minor.
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 makes it possible to assign I2C objects (machine.I2C0,
machine.I2C1, etc.) without needing to take a pointer.
This is important especially in the future when I2C may be driven using
DMA and the machine.I2C type needs to store some state.
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.
This commit lets the compiler know about interrupts and allows
optimizations to be performed based on that: interrupts are eliminated
when they appear to be unused in a program. This is done with a new
pseudo-call (runtime/interrupt.New) that is treated specially by the
compiler.
Add a target for the Adafruit Circuit Playground Bluefruit, which is
based on the nRF52840. Adds the necessary code for the machine
package and the json and linker script files in the targets directory.
The machine package code is based on board_circuitplay_express.go,
with modifications made by consulting the wiring diagram on the
adafruit website here:
https://learn.adafruit.com/adafruit-circuit-playground-bluefruit/downloads
Also adds support to the uf2 conversion packacge to set the familyID
field. The Circuit Playground Bluefruit firmware rejects uf2 files
without the family id set to 0xADA52840 (and without the flag specifying
that the family id is present).
These all-caps constants aren't in the Go style, so rename it to
CPUFrequency (which is more aligned with Go style). Additionally, make
it a function so that it is possible to add support for changing the
frequency in the future.
Tested by running `make smoketest`. None of the outputs did change.
