COM port detected a Receive Overrun Error

This warning is is related to load on the COM port and the CPUs ability to service the COM port interrupts (ie. CPU load and interrupt priorities). The COM port typically has two 16 byte buffers (on a UART/Super IO chip). One for transmit and one for receive. The "COM port detected a Receive Overrun Error" occurs if data is received by the UART receive buffer when the receive FIFO buffer is full. That is, before a COM port interrupt is serviced by the CPU to copy the receive buffer to RAM. The COM port interrupt trigger level is a Windows setting, this is typically defaulted to 14 - ie. generate a CPU interrupt when 14 of the 16 bytes in the UART buffer are full. In this case the last byte in the UART receive FIFO is overwritten and that data is lost.

You could try changing:
(1) the COM port speed (reduce)
(2) the COM port duty cycle (reduce)
(3) the UART settings (please see: http://support.Microsoft.com/kb/131016/EN-US/ ). For example reduce both buffers to 8 (ensure that the transmit FIFO is not larger than the receive FIFO).
(4) If you are running the CD test at the same time, then you should check that the CD/DVD drive is on a controller that is set to DMA rather than PIO (as PIO will lead to a large number of CPU interrupts, which will impact the servicing of the COM port interrupt). I understand that the controller can automatically drop from DMA to PIO mode based on the number errors (such as a badly scratched CD/DVD).

Regards,
Ian

my system (winXP SP2, Intel Celeron 440 2GHz) running serial loopback test fail:
log:
PassMark BurnInTest Log file - http://www.passmark.com
================================================== ======
BurnInTest V5.3 Pro 1014
Logging detail level: Normal
******************
SYSTEM INFORMATION
******************
Computer Name: GEG
Date: 07/23/08 16:47:36
Operating system: Windows XP Professional Service Pack 2 build 2600
Number of CPUs: 1
CPU manufacturer: GenuineIntel
CPU type: Intel(R) Celeron(R) CPU 440 @ 2.00GHz
CPU features: MMX SSE SSE2 SSE3 DEP PAE
CPU1 speed: 1994.7 MHz
CPU L2 Cache: 512 KB
RAM: 446 MB
Video card: VIA Chrome9 HC IGP Family (Resolution: 800x600x32)
Disk drive: Model Hitachi HDS721680PLA380 IBM PVFB44ZLSB3UXEP21OABCA (Size: 74.5GB)
Optical drive: SONY DVD RW AW-G170S USB Device

**************
RESULT SUMMARY
**************
Test Start time: Wed Jul 23 16:26:40 2008
Test Stop time: Wed Jul 23 16:41:43 2008
Test Duration: 000h 15m 03s
Test Name Cycles Operations Result Errors Last Error
Serial Port 1 18 763392 FAIL 10 COM port detected a Receive Overrun Error
Serial Port 2 16 878398 FAIL 3 COM port detected a Receive Overrun Error
TEST RUN FAILED
******************
DETAILED EVENT LOG
******************
LOG NOTE: 2008-07-23 16:26:40, Status, Main Tests started
CRITICAL : 2008-07-23 16:27:38, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:27:38, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 2 Transferred: 94 Handle:000002A4 Total: 26994, ErrorCode: 0
CRITICAL : 2008-07-23 16:27:58, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:27:58, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 0 Transferred: 100 Handle:000002A4 Total: 30394, ErrorCode: 0
LOG NOTE: 2008-07-23 16:27:58, Serial, Error at byte 80 of 100 (0x58 trans., 0x6c rec'd)
CRITICAL : 2008-07-23 16:28:38, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:28:38, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 2 Transferred: 98 Handle:000002A4 Total: 43892, ErrorCode: 0
CRITICAL : 2008-07-23 16:29:58, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:29:58, Serial, \\.\COM2 Speed: 9600baud BlockSize: 100 BlockNum: 0 Transferred: 100 Handle:000002A0 Total: 101200, ErrorCode: 0
LOG NOTE: 2008-07-23 16:29:58, Serial, Error at byte 40 of 100 (0x3f trans., 0x4d rec'd)
CRITICAL : 2008-07-23 16:30:38, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:30:38, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 1 Transferred: 100 Handle:00000260 Total: 98392, ErrorCode: 0
LOG NOTE: 2008-07-23 16:30:38, Serial, Error at byte 52 of 100 (0x2f trans., 0xc2 rec'd)
CRITICAL : 2008-07-23 16:31:08, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:31:08, Serial, \\.\COM2 Speed: 9600baud BlockSize: 100 BlockNum: 2 Transferred: 98 Handle:000002A0 Total: 131198, ErrorCode: 0
CRITICAL : 2008-07-23 16:31:17, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:31:17, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 1 Transferred: 100 Handle:00000260 Total: 114192, ErrorCode: 0
LOG NOTE: 2008-07-23 16:31:17, Serial, Error at byte 92 of 100 (0x44 trans., 0x 1 rec'd)
CRITICAL : 2008-07-23 16:33:48, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:33:48, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 0 Transferred: 100 Handle:000002A0 Total: 180592, ErrorCode: 0
LOG NOTE: 2008-07-23 16:33:48, Serial, Error at byte 64 of 100 (0x 5 trans., 0x3a rec'd)
CRITICAL : 2008-07-23 16:36:57, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:36:57, Serial, \\.\COM2 Speed: 9600baud BlockSize: 100 BlockNum: 1 Transferred: 100 Handle:00000260 Total: 298498, ErrorCode: 0
LOG NOTE: 2008-07-23 16:36:57, Serial, Error at byte 80 of 100 (0x c trans., 0x16 rec'd)
CRITICAL : 2008-07-23 16:37:07, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:37:07, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 1 Transferred: 100 Handle:000002A0 Total: 272592, ErrorCode: 0
LOG NOTE: 2008-07-23 16:37:07, Serial, Error at byte 92 of 100 (0x35 trans., 0xa7 rec'd)
CRITICAL : 2008-07-23 16:37:38, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:37:38, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 0 Transferred: 100 Handle:00000260 Total: 281092, ErrorCode: 0
LOG NOTE: 2008-07-23 16:37:38, Serial, Error at byte 40 of 100 (0xd2 trans., 0xbf rec'd)
CRITICAL : 2008-07-23 16:38:28, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:38:28, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 1 Transferred: 100 Handle:00000260 Total: 299592, ErrorCode: 0
LOG NOTE: 2008-07-23 16:38:28, Serial, Error at byte 92 of 100 (0x 4 trans., 0x 1 rec'd)
CRITICAL : 2008-07-23 16:40:18, Serial, COM port detected a Receive Overrun Error
LOG NOTE: 2008-07-23 16:40:18, Serial, \\.\COM1 Speed: 9600baud BlockSize: 100 BlockNum: 1 Transferred: 100 Handle:00000260 Total: 347192, ErrorCode: 0
LOG NOTE: 2008-07-23 16:40:18, Serial, Error at byte 12 of 100 (0x9b trans., 0x17 rec'd)
LOG NOTE: 2008-07-23 16:41:45, Status, Test run stopped

tried to disable UART,lower UART.But still fail.
any idea?

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COM port detected a Receive Overrun Error

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