* add gosched calls to UART
* add UART.flush() stubs for all supported architectures
* add comment un uart.go on flush functionality
* uart.writeByte as base of UART usage
* fix NXP having duplicate WriteByte
* fix writeByte not returning error on some platforms
* add flush method for fe310 device
* check for error in WriteByte call to writeByte
Some targets used capital PullUp/PullDown, while the documented standard
is Pullup/Pulldown. This commit fixes this mismatch, while preserving
compatibility with aliases that are marked deprecated.
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.