How to Obtain Best Timing Accuracy

Many RS232 monitoring applications – including Docklight – can only provide limited accuracy when it comes to time tagging the serial data. As a result, data from the two different communication directions can be displayed in chronologically incorrect order, or several telegrams from one communication direction can appear as one chunk of data.

This behavior is not caused by poor programming, but is rather characteristic for a PC/Windows system, and the various hardware and software layers involved. Unspecified delays and timing inaccuracies can be introduced by:

•	The COM device’s chipset, e.g. the internal FIFO (First-In-First-Out) data buffer.

•	The USB bus transfer (for USB to Serial converters).

•	The serial device driver for Windows.

•	The task/process scheduling in a multitasking operating system like Windows.

•	The accuracy of the date/time provider.

Docklight comes with a very accurate date/time provider with milliseconds granularity, but it still needs to accept the restrictions from the hardware and software environment around it.

Here is what you can do to minimize additional delays and inaccuracies and achieve a typical time tagging accuracy of 5 milliseconds or better:

1.	Get our Docklight Tap for lowest USB-related latency times. Or use on-board RS232 ports, if still available on your PC.

2.	Choose External / High Priority Process Mode in the Tools > Expert Options... dialog.

3.	When monitoring high amounts of data, use the recommendations from the previous section How to Increase the Processing Speed... to avoid input buffer overflows and that the computer become irresponsive because of high CPU usage.

NOTE: The Expert Options... recommended above will change the overall system balance and must be used with care. Best results can be achieved only when logged in as an Administrator. Please make sure you understood the remarks and warning in the documentation.