Previously, the machine.UART0 object had two meanings:
- it was the first UART on the chip
- it was the default output for println
These two meanings conflict, and resulted in workarounds like:
- Defining UART0 to refer to the USB-CDC interface (atsamd21,
atsamd51, nrf52840), even though that clearly isn't an UART.
- Defining NRF_UART0 to avoid a conflict with UART0 (which was
redefined as a USB-CDC interface).
- Defining aliases like UART0 = UART1, which refer to the same
hardware peripheral (stm32).
This commit changes this to use a new machine.Serial object for the
default serial port. It might refer to the first or second UART
depending on the board, or even to the USB-CDC interface. Also, UART0
now really refers to the first UART on the chip, no longer to a USB-CDC
interface.
The changes in the runtime package are all just search+replace. The
changes in the machine package are a mixture of search+replace and
manual modifications.
This commit does not affect binary size, in fact it doesn't affect the
resulting binary at all.
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.
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.
