The PMLM program that comes with SIO is a "Poor Man's Line
Monitor" that is able to show you what is happening on the serial
ports. It's a great little tool.

But it got me wondering how it's done. At first I thought it was a simple
matter of opening the com port as READONLY and DENYNONE, and this works
reasonably well. Then you can use DosDevIoctl calls to get info from the
serial port device driver.

But then, when I started up Faxworks, Faxworks (which uses its own comms
driver) was denied access to the port because I still had an open file
handle on the port. Makes sense, except that somehow PMLM manages to simply
step aside when Faxworks is running. It doesn't report any activity, but it
also doesn't interfere.


Anyone got any ideas about how PMLM does it?

simeon

--- FleetStreet 1.10 NR