160 baud ALDL data - reading on a PC, counter 0?

[steve ravet]

Peter Gargano wrote:
> Does anyone know what frequency the AT clocks counter 0 at?
> All my documentation says it's at 0.84 uSec (micro seconds)
> BUT my measurements on a couple of Pentium and 486 machines
> indicate that it's closer to 0.43 uSec AND that it counts
> in lots of 2 (ie. reading counter 0 always reads an even
> binary number). Now I know XTs and early ATs did clock counter
> 0 at 1.19 MHz, but when did they change to closer to 2 Mhz, or
> am I losing the plot?

I've got the AT tech ref manual at home, can take a look if I remember. 
Like someone else said, it's not too surprising that it's off...  The
timing delay should probably be user settable, unless you can find
something else reliable in the machine to calibrate it.

> 
> I'm going to "tidy up" this bit of code and make it available
> to show the raw 160 baud ALDL data stream in real time. I'm
> not going to try and decode the data stream because I'm going
> to give away this code to whoever wants it. It'll be able to
> run on an XT AND it should also run fine in a DOS box too. Any
> thoughts on the best way to display this raw data?

Plain HEX dump is probably easiest and most useful.  Wait for 9 ones in
a row, then dump the succeeding bytes, stripping the leading one.

--steve

> 
> regards,
> --
> Peter Gargano

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com