MFp4:
MFp4:

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...

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase