[SDR] beagleboard I/O

[aahill at rockwellcollins.com]

Barry asked for a summary of beagleboard I/O options for our daughtercard.

Here's what I've found:
The favored interface is likely the two McBSPs (multi-channel buffered 
serial ports) in the expansion connector.
The McBSPs have independent transmit and receive data pins with one bit 
transferred each clock cycle.

When I used TI's McBSPs in a DSP board we found that these serial ports 
were practically limited to clock speeds of 50 to 60 MHz.
We decided to run things at 33 MHz and that was with controlled traces and 
no connectors.

For back of the envelope calculations using both ports I'd not expect more 
that 50 Mbit/sec bidirectional data rates between the beagleboard and 
daughtercard.
Testing may reveal that we can safely increase this clock speed but for 
now I wouldn't bet on it.

-Adrian (KC0YOI)
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