The problem here is that the timing requirements are in a difficult
range. The timing is too slow to do busy waiting, but too fast to
do anything from user space. I'd recommend you do the following:
Use the baud rate generator of the rs232 interface to generate
the required interrupt rate (yes, quite like the baycom ser12 stuff),
such as 1k ints/s and then control the output port via
inb/outb. This really isn't so hard, don't be afraid, it's easier
than under DOS...
Interrupt latency differs from setup to setup. If you have an
IDE disk and do not enable interrupts with hdparm, interrupt
latency sucks hard, but otherwise it's good (less than 100us)
73s
Tom