jp57+@andrew.cmu.edu (Jefferson Provost) (01/09/91)
Hi,
I'm currently working on a program that's highly dependant on the use of
the Vertical Retrace Signal for timing. It was developed on a Mac IIx &
a Mac IIfx, and it works correctly on them. Now we've acquired a IIsi
as a third development machine. Here's where the problem starts.
In initializing the system we get the slot number of the graphic device
that we'll use with AttachVBL, etc, from 'scrn' resource 0. We use the
slot number for the first screen in 'scrn' resource as the slot for our
screen. (that we will always use the first screen is possibly not a
valid assumption, but we have yet to work on machines with multiple
screens/graphic cards).
The rub is that the IIsi has built in graphics and no graphics card, so
the slot number in the 'scrn' resource is 0. The programmers who wrote
the code (not me) assumed that a 0 slot number would be an error
condition and trapped it as such. Now that won't work. I removed the
code that caught the 0 slot number as an error and things _seemed_ to
work fine, but I haven't had a chance to check the timing.
I need to know two things:
1) Is 0 the correct slot number for the built-in graphics on the IIsi?
2) Will the Vertical Retrace Manager routines work correctly with a slot
number of 0.
The result code from SlotVInstall is 0 (noErr) when I give it a slot
number of 0, which leads me to believe that everything is O.K. but
there's still the possibility (however slight) of a system bug or
oversight on the part of Apple.
Any new insight will be appreciated, post or email me.
Thanx,
Jeff
|Jefferson Provost -- jp57+@andrew.cmu.edu
|---
|"Had my hand on a dollar bill, and the dollar bill flew away,
| but the sun is shining down on me and it's here to stay."