Sys V Targa driver

[Craig Anderson]

I am writing a 386ix v2.0 driver for the Truevision Targa 16 card.
I am wondering how best to have the driver wait for vertical blanking.
Vertical blanking is determined by polling an I/O register for the
line number.

I've come up with 3 ideas on how to do this:

1) Have the ioctl poll the I/O register for vertical interval.
   It seems drastic for an ioctl routine to be polling for up 1/15 sec.
2) Arrange for a Poll routine to wake the driver ioctl on vertical
   interval.
   a) Is the poll routine always active?
   b) Should I worry about the overhead of using this?
2) Use a variable delay to guess when vertical interval is.
   The current line count could be used to estimate the number
   of clock ticks till vertical interval.

Any advice on this will be much appreciated.  This is a hobby
project, so I'd be happy to share notes or code with any one
interested.

Craig H. Anderson
UUCP    (ncar,isis,boulder,nbires)!scicom!craig
DOMAIN  craig at scicom.alphacdc.com