[Simulavr-devel] Simple UART support

[ken restivo]

And here it is: a patch against today's CVS which adds rudimentary UART support.

What it does:
        - Read/write UART data from apps which use a simple tight polled loop
        - Accept an arg (--uart-tty=/path) from which to send/receive UART chars
        - Check RXEN/TXEN and complain if the app doesn't set them properly
        - Let the app read/write UDR, UBRR, UCSRA, and UCSRB.
        - Defines all the bits and masks for my part (atmega163).

What it does not:
        - UART interrupts
        - Deal with RXC/TXC bits intelligently.
        - Any tty mode-mangling. I figured the sim shouldn't; let the user do 
it.
        - Network or UNIX sockets, though it'd be pretty easy to implement.
        - Other UART register layouts from other parts, or multiple UARTS.

I'm using it with a /dev/pts/xx on linux, simulating a mega163, and all is
well so far. This should get me through testing/debugging my app (I'm really 
fatigued with object-oriented programming at this point, and am chomping at 
the bit to get back to my assembly code again! ;-). But, at some point soon, 
I'll need to add interrupt support, if someone else doesn't do it first.

Oh, and I wasn't sure where to put the read/write functions, so I left them in 
main.c. Also all the opening of fd's and adding of callbacks probably wants to 
get moved into a setup_uart_external() or some such method, but I wasn't sure 
where to put it or what to call it, so I left all that stuff sitting there 
loose in main(). My apologies.

-ken
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