PCI write oddity

[Daniel O'Connor]

Hi,
I have a custom device driver for a PCI RS485 card - it has a 16550 and 
a PLX PCI bridge on it and I recently found something quite odd.

We used to run the link at 9600 but with some more recent modules we've 
decided to up it to 115200, so I changed the baud rate easily enough.. 

However while the bit rate is correct each byte going out has a 1 
millisecond delay(!). What is really odd is that when I added some 
debugging to log how long each write to the FIFO register took I 
discovered it was 1 millisecond.

Reads from the same register take ~5 usec which seems more like it.

Does anyone have any idea why it would be so damn slow?

-- 
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C
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