We all have to accept that doing any sort of accurate timing operation
on a PC is futile - whether Soundacard, serial port or, even worse, by
software timing.   Therefore some sort of external interface really
should be used to resynchronise Tx and Rx data samples        .

Hmm, perhaps not all is lost. The Pentium II class CPUs and the Athlons
do have the so-called Performance Timer, an hardware timer
that can be queried through Windoze APIs, with resolution around 1 usec.

This however would rule out old Pentiums, 486 and the AMD K6, which do
not have that counter.

73   Alberto   I2PHD