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.
It is always implemented exactly the same way (as an uint8) so there is
no reason to implement it in each target separately.
This also makes it easier to add some documentation to it.
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.
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.
Instead of only allowing a limited number of speeds, use the provided
speed as an upper bound on the allowed speed. The reasoning is that
picking a higher speed than requrested will likely result in malfunction
while picking a lower speed will usually only result in slower
operation.
This behavior matches the ESP32 at least.
There was what appears to be a race condition in the Tx function. While
it would work fine in many cases, when there were interrupts (such as
when using BLE), the function would just hang waiting for `EVENTS_READY`
to arrive.
I think what was happening was that the `spi.Bus.RXD.Get()` would start
the next transfer, which would complete (and generate an event) before
`EVENTS_READY` was reset to 0. The fix is easy: clear `EVENTS_READY`
before doing something that can trigger an event.
I believe I've seen this bug before on the PineTime but I couldn't find
the issue back then.
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.
Comparing slices against nil currently causes the slice to escape, due
to a limitation in LLVM 8. This leads to lots of unnecessary heap
allocations. With LLVM 9 and some modifications to TinyGo, this should
be fixed. However, this commit is an easy win right now.
Returning an error when both slices are nil is not necessary, when the
check is left out it should just do nothing.
For updating an SPI screen using the st7735 driver, this results in a
~7% performance win.
The SPI peripheral in the nrf chips support double buffering, which
makes it possible to keep sending continuously. This change introduces
double buffering on the nrf chips, which should improve SPI performance.
Tested on the pca10040 (nrf52832).
* machine/uart: add core support for multiple UARTs by allowing for multiple RingBuffers
* machine/uart: complete core support for multiple UARTs
* machine/uart: no need to store pointer to UART, better to treat like I2C and SPI
* machine/uart: increase ring buffer size to 128 bytes
* machine/uart: improve godocs comments and use comma-ok idiom for buffer Put/Get methods
The default priority is 0 (highest) which is reserved by the SoftDevice.
For normal operation the exact priority level doesn't matter, only the
relative priority matters. So this change makes the code compatible with
the SoftDevice without actually changing the behavior.
