Make serial ports more robust and reliable. Make non-console ports
work. This might have broken skyeye stuff.
o Introduce ping-pong receive buffers.
o Use DMA to copy characters directly into memory.
o Support baud rates other than 115200
o Use 1 stop bit when 1 stop bit is requested (otherwise 2 were used,
which caused dropped characters when received in bursts).
o Use 1.5 stop bits for 5-bit bytes, and 2 stop bits otherwise when 2
stop bits were requested.
o Actually update line parameters.
o Fix comments
o Move init into attach
o Tweaks to TX interrupt registers to get them reliable and non-storming.
o harvest data in ipend since the latency between it and the callback
was too long. This likely is how it should be, I don't know why I deferred
things to the callback before.
o disable all interrupts in console init. We don't want interrupts until
we turn on an ISR.
o cosmetic tweaks
o Automatically detect of the TIMEOUT interrupt is supported. If so, use
it so we get better CPU utilization. Otherwise do a character at a time
RX. Good news here is that it seems we have enough CPU and low enough
fast interrupt latency to do this reliably.
o Don't read USART_CR. It is a write-only register.
o start to implement bus_ioctl. Do BAUD now...
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