PCI/AGP bridge latency causes serial port CE_OVERRUN error..

Archived from groups: comp.sys.laptops,comp.sys.ibm.pc.hardware.chips (More info?)

Hi Gurus,

I have an IBM ThinkPad T21 Laptop (Pentium III-750Mhz) running Windows
2000. Using serial port COM1 at 115kbaud, it experiences CE_OVERRUN
errors from ClearCommError in the Win32 API. This indicates that the
serial port is losing bytes due to a FIFO overrun in the
16550-compatible UART. It happens even with "Use FIFO buffers" and the
lowest Receive Buffer threshold setting in the Advanced Settings
control panel for COM1.

Minimising/maximising Internet Explorer, resising the window or
dragging it around is enough to cause the occasional CE_OVERRUN error.
By running SiSoft SANDRA (http://www.sisoftware.net/) I found that the
PCI Latency Timer for the PCI/AGP bridge appears to be set too high
(128), which would cause servicing of the UART to be blocked for too
long when performing video accesses. I can't find a BIOS setting to
reduce this latency timer value, and none of the PCI Latency Timer
setting utilities I've found on the 'net so far seem to run on Windows
2000. Does anyone know any way to adjust the Latency Timer setting, or
another fix to this problem?

Thanks,
Graham
Computer Systems Engineer