ast@botter.UUCP (06/10/87)
A while back sheu@gitpyr.UUCP (Der-Ru Sheu) posted the following fix to make the EGA board work: > Following is a brief explanation. There is a register inside the EGA > sequencer, to tell 'Extended Memory' (those beyond 64K, or 16K in fact, > since 4 color planes share the same memory space) is installed or not. > By cheating the hardware no extended memory installed, it will perform > exactly like a CGA (but with a much better resolution, of course). > > I added the following three lines into 'main.c' (at the very begin). > I believe this modification won't cause any problem with mono or CGA cards, > since those I/O addresses are not used anywhere else. However, I don't have > the hardware to test it with. > > port_out(0x3c4, 4); /* Select register inside the sequencer */ > port_out(0x3c5, 1); /* No extended memory, take my word for it. */ > /* That's all! Just as I said, it's simpler. (Optional, :-) ) */ > We finally tried it here and it didn't quite work. However, we tried it on a Zenith Z-248 EGA card, which may be different from IBM's. Since it is such a simple and elegant fix, I would like to hack it into shape. Has anyone else tried it, and if so, please post your findings. Andy Tanenbaum (ast@cs.vu.nl).
vizard@dartvax.UUCP (Todd Krein) (06/15/87)
In article <1207@botter.cs.vu.nl>, ast@cs.vu.nl (Andy Tanenbaum) writes: > A while back sheu@gitpyr.UUCP (Der-Ru Sheu) posted the following fix > to make the EGA board work: > > > Following is a brief explanation. There is a register inside the EGA > > sequencer, to tell 'Extended Memory' (those beyond 64K, or 16K in fact, > > since 4 color planes share the same memory space) is installed or not. > > By cheating the hardware no extended memory installed, it will perform > > exactly like a CGA (but with a much better resolution, of course). > > > > port_out(0x3c4, 4); /* Select register inside the sequencer */ > > port_out(0x3c5, 1); /* No extended memory, take my word for it. */ > > > We finally tried it here and it didn't quite work. However, we tried it on a > Zenith Z-248 EGA card, which may be different from IBM's. Since it is I just got an NEC GB-1 (or a renamed EVA-480). This nice fix won't work on it, or any board using Tseng Labs chips, as this implementation doesn't have a comparable register. If you do have such a board, you'll have to use the new scrolling routines that someone (I don't remember his name) posted to fix it. I've installed them, and thay work great. (Snaps to that nameless author). Perhaps this is the problem... Todd Krein vizard@dartvax