Author: jason (dnvrdslgw13poold17.dnvr.uswest.net)
Date: 09-28-2002 18:47
Of course, raster ints are the same on the STE as the ST. You have two choices for them. You can use the HBL vector or you can use the MFP-Timer B vector. Timer B event-count interupts allow you to generate an exception on every _visible_ scan line. Whereas HBL interupts execute on _every_ scan line (including the top and bottom borders).
The accuracy of the interupt timing depends on the how much time the processor spends on an instruction or another exception before servicing the interupts. for example, code with a lot of big MOVEM.Ls will result in very unstable interupts because the processor will likely be busy with the MOVEMs when the interupt is triggered.
Which type would you like code for? I can send you some, but i'll have to retrieve it from my falcon first. Here are some addresses that are helpfull.
$68.L: HBL exception vector (set priority level in 680x0 status register to one before using)
$120.L : MFP-Timer B exception vector (set up Timer B for event count mode before using)
bit #0 in the above control registers selects Timer B.
$fffffa1b.B: Timer B control
write $08 to this address to put timer B in event count mode
$fffffa21.B: Timer B Data
write the number of events to count before the next interupt here (i.e. write 1 for every scanline or 2 to wait a scanline etc.)
