robert-s@cs.aukuni.ac.nz (Robert Sheehan ) (04/15/91)
After careful scrutiny of what was going on I found out that the problem was a piece of code which checked vertical blanking. ECD2: bit $C019 bmi $ECD2 ECD7: bit $C019 bpl $ECD7 rts Now as far as I can make out this code should wait for the start and end of the vertical blanking period (different order according to whether running on a GS or IIe). On my IIc the second test always loops. I fiddled around and found out that $C019 always returns $1D (I think) on my IIc. Anyone know anything about this? I can think of several possibilities: my ZipChip, my Z-Ram Ultra II or my IIc. In this part of the world our IIc's were made in Ireland (even though California is a lot closer) because of the keyboard layout and 50 Hz power. This means VBL is at 50 Hz on my machine. BTW VBL interrupts work properly as I have played with them in my own programs. Another thing which may or may not be related is that after patching PipeDream to run it won't recognize my mouse. Robert Sheehan. -- New administrater uofa.
dlyons@Apple.COM (David A. Lyons) (04/15/91)
In article <robert-s.671666320@cs7.cs.aukuni.ac.nz> robert-s@cs.aukuni.ac.nz (Robert Sheehan ) writes: >After careful scrutiny of what was going on I found out that the problem was >a piece of code which checked vertical blanking. > >ECD2: bit $C019 > bmi $ECD2 >ECD7: bit $C019 > bpl $ECD7 > rts > >Now as far as I can make out this code should wait for the start and end of >the vertical blanking period (different order according to whether running >on a GS or IIe). > >On my IIc the second test always loops. I fiddled around and found out that >$C019 always returns $1D (I think) on my IIc. Anyone know anything about this? $C019 does not work quite the same on the IIc and IIc Plus as on the IIe and IIgs. See Apple IIc Technical Note #9, November 1990. -- David A. Lyons, Apple Computer, Inc. | DAL Systems Apple II System Software Engineer | P.O. Box 875 America Online: Dave Lyons | Cupertino, CA 95015-0875 GEnie: D.LYONS2 or DAVE.LYONS CompuServe: 72177,3233 Internet/BITNET: dlyons@apple.com UUCP: ...!ames!apple!dlyons My opinions are my own, not Apple's.
alfter@nevada.edu (SCOTT ALFTER) (04/15/91)
The IIc uses a different VBL mechanism than the IIe and IIGS. Don't ask me why. :-) There's a tech note that describes it, though. Scott Alfter-----------------------------_/_---------------------------- Support Operation Apple Storm! / v \ Apple II: Internet: alfter@uns-helios.nevada.edu ( ( the power to be your best! GEnie: S.ALFTER \_^_/