b-davis%utah-cs@sri-unix.UUCP (11/24/83)
From: b-davis@utah-cs (Brad Davis) I have been working on a device driver for a char device (a serial port plotter) in such a way that the driver knows the format of the plotter commands but the application program doesn't. I set up a char device and sent 20 bytes to it in one buffer with the int 21h ah = 40h function call. In poking around in the driver I found that DOS was calling my routine once for every byte I was sending. Since I send down one buffer of 20 bytes is there some way to make DOS do one call to my driver and write all 20 bytes at the same time? I think I could make the driver a blocked device but that sort of defeats the idea of having char devices. I would also be interested in hearing from any others who have written device drivers. By the way, the reason that the NUL device can't be replaced is that DOS points at it first and loads the other drivers after it. If you load two drivers with the same name then the last one loaded is first in the list and will get invoked. The hard and floppy disk are under the same driver. Brad Davis b-davis@utah-cs