HELP WITH PI'S PARALLEL PORT!!

[Sidney Fels]

I am currently trying to get my PI to talk to a speech synthesizer through
the Centronics port.  I have called the hot line but haven't got anything
useful back from them yet.  When I look at the port on a logic analyzer
it appears that the SGI is sending duplicate bytes to the synthesizer.
The strobe signal for these duplicate bytes is a very short glitch
which suggests that the SGI is doing something wrong.  My current belief about 
what seems to be happening is that the SGI Centronics port is not responding 
to the ACKNOWLEDGE signal properly.  One theory I have is that the PI cannot 
handle the data rate requested by the synthesizer.  Does anyone know of 
the response time of the SGI to parallel port byte requests, i.e. when 
the BUSY signal drops to 0 how long before data is put on the line with 
an accompanying strobe, assuming that my process is waiting on the write 
call with extra high priority?  As well, how long does it take the SGI
to deal with a received ACK signal?

The synthesizer works perfectly when connected to an IBM PC with 
either the ACK connected or disconnected. When ACK is connected the timing 
of the handshaking is correct.  If I disconnect the ACK signal the SGI 
hangs on the write call.  If I tie ACK to BUSY it still hangs on the write.  

Has anyone out there used the centronics port and encountered any difficulties?
Better still, anyone know what may be the problem?  Is there someway to 
force the SGI to ignore the ACK signal and just send a byte when BUSY goes
low?  

Any help with this will be most appreciated.

Thanks,

Sidney Fels
University of Toronto
ssfels at ai.toronto.edu
(416) 978-7453
Fax: (416) 978-1455