During the Digi async driver installation, one of the files installed into the DIGI$DRIVER logical is a file called SPACE.MAR. This file has a line near the bottom of it, which contains a value called the polling interval. The polling interval is set at 20 polls/second by default, and is the best balance we've found between processing load on the intelligent Digi card versus processing load on the system.

Basically, this polling interval is the rate at which our driver checks for data and hardware signal state changes such as when using hardware flow control. We pass information from the firmware to the driver to the OS, and the polling interval is what determines how fast we do that.

The default value of 20 polls/second is equivalent to a polling interval of 50mS. The range of this value is 1-10,000 polls/second. 10,000 polls/second is virtually no delay, but very tasking on a system since the system is doing all processing of the data rather than the intelligent Digi card. If adjustment of the polling interval is needed at all, it is best to do this in steps. Try setting it first to a value of 500 polls/second, which is a 2mS interval. You could then adjust further if necessary to find the best balance between system performance and data latency.

After the SPACE.MAR file is edited, DG_SETUP.COM will need to be run, and relink option chosen. After the kernel relinks, the system will need to be rebooted. Once up and running again you can test to see if the current interval setting suits your needs.

Although we are one possible source of delay in data traveling from point A to point B, every link in the data path adds its own inherent delay to create the overall latency. Hopefully by following these steps, you can minimize any impact our driver will have in your timing-sensitive environment.