Precision Fixed Workstations

Last reply by 04-07-2021 Solved
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2 Bronze

serial port overrun

Precision Tower 3630 running Windows 10 64bit Builtin COM1 Serial port works but has overruns on input, some of the characters received are lost (115K baud). Device Manager lists COM1 under C240 LPC controller Driver listed as version 10.0.16299.15 from Microsoft, dated 2006 System claims the driver is up to date Is there a more recent driver, or something to be enabled in BIOS to get COM1 to work properly?
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I already played with that driver settings, but it does not help.


Then try installing an add-in serial port card that has a much deeper FIFO than the standard 16550 -- such as the 16650, 16750, 16850, 16950 or 161050 UART.



JSz, thank you for the tip with this Fifo setting!

After I exactly used your recommended setting and after a reboot, it seems that the serial port now is handled error free, so no characters are missing.

I will watch the serial ports behaviour the next days, if there are still some characters missing, I will buy a serial add-in card with a better UART.


If you still have errors, you can try to set the trigger level for the receive buffer to 4


The explanation behind this is that:
with (14), 3 more characters will overrun the FIFO
with (8), 9 more chars will be needed for overrun
and with (4) 13 more chars will be needed to overrun the UART's FIFO (assuming a standard 16550)

The lower trigger numbers result in higher interrupt frequencies, but the chance of overrun can lessen very significantly.   Methinks the default should be 8, not 14, but I'm not in charge of setting that.

With the higher numbered UARTs the buffer can be as large as 128 - 256 bytes, which is a heck of a lot more than the standard 16.



JSz, Thank you again for the explanation!
It is always helpful to know the technical background.

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