serial port and inter-character delay greater than 1ms

wfong — Wed, 24 Jun 2009 08:08:22 GMT

hi all

We have a proprietary smart card reader connected to the serial port that seems to have some difficulty working consistently when connected to a guest virtual machine (windows xp).

The host is running windows xp and vmware workstation 6.0.5 build 109488.

It seems that the inter-character delay between the commands to
the card reader is causing the instability. Any delay greater than 1ms denotes the end of a command to the card reader device.

Sometimes the whole command string reaches the card reader and all works fine, however other times there is a delay of about 4ms between characters.

This occurs about 5% of the time when doing simple polling commands, however the errors steadily increase when commands that require large amounts of data to be written to a card are sent.

These are the config items that I put in the vmx to try and "speed" up the serial port in the virtual machine.

I got the ideas from http://www.sanbarrow.com/vmx/vmx-serial-ports.html

serial0.present = "TRUE"
serial0.fileType = "device"
serial0.fileName = "COM1"
serial0.autodetect = "FALSE"
serial0.hardwareFlowControl = "FALSE"
serial0.tryNoRxLoss = "FALSE"
serial0.yieldOnMsrRead = "TRUE"
serial0.pipe.charTimePercent = "10"

We have confirmed that the card reader + serial port work fine on the host machine natively. It seems that the serial port driver under vmware has some latency issue ?

Regards

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serial port and inter-character delay greater than 1ms