README: sample-sdlc

This is a simple example demonstrating use of a SeaMAC device in SDLC
mode.  This sample consists of two applications: a sender and a receiver.  The
applications expect to be given the device ids of two SeaMAC serial ports
connected together by a null modem.  The sender's TELEMENT clock signal must
also be routed to the receiver's TXCLK and RXCLK pins.

The receive application should be started before the send application.  The
first argument for each sample is the SeaMAC serial port desired to preform
the operations on.  The send application can optionally take one more argument:
message size.

$ receive-sdlc /dev/ttySM1
$ send-sdlc /dev/ttySM0 8

All received data is captured to the file "data" in the directory from which
the receive application is run.  The message(s) sent by the send application
consist of the specified number of data bytes cycling from 0 to 255.

