At 10:14 AM 10/23/2001 +1000, you wrote:
>>The above is correct. VBLANK just blanks the video output. The sync line
>>is still active. VBLANK is a lazy way to get a black screen. In this case,
>>they are using VBLANK to create the 3 lines of equalization pulses before
>>VSYNC. Then they do 3 lines of VSYNC. You don't mention when they turn off
>>VBLANK, and I don't have the code in front of me. But it's perfectly
>>acceptable to do the following:
>>
>>turn on VBLANK
>>turn on VSYNC
>>turn off SYNC
>>turn off VBLANK
>
As a follow up, I removed my vsyncing code to get absolute scanlines and
found this interesting:
---------
TIA_w - VBLANK Start - Scanline is 30
TIA_w - WSYNC - HowizPos is 17
TIA_w - WSYNC - HowizPos is 8
TIA_w - WSYNC - HowizPos is 8
TIA_w - VSYNC Start Scanline = 33 HorizPos = 8
TIA_w - WSYNC - HowizPos is 17
TIA_w - WSYNC - HowizPos is 8
TIA_w - WSYNC - HowizPos is 14
TIA_w - VSYNC Stop Scanline = 36 HorizPos = 8
Background Color set to 234
TIA_w - WSYNC - HowizPos is 143
TIA_w - WSYNC - HowizPos is 41
TIA_w - VBLANK Stop - Scanline is 171
------------
Repeated always - VBLANK for 3 lines, then VSYNC for 3 lines then stop
VBLANK after 141 lines. This is without any VSYNC emulation with the
screen updates. So, what should the scanline numbers *actually* be from an
emulation view? And does this output make real sense to 2600 guru's? :)
This machine is nuts - I am impressed that so much great software was
developed for it ;)
Ben
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