On Tuesday 15 June 2004 03:34, Jeff Walther wrote: > At 15:00 -0400 06/14/2004, Compact Macs wrote: > >Date: Sun, 13 Jun 2004 16:39:32 -0400 (EDT) > >From: Nathan Raymond <[EMAIL PROTECTED]> > > > >On Sun, 13 Jun 2004, Jeff Walther wrote: > >> I'm sure these methods have been worked out in detail better than I can > >> reinvent them, and there is probably a comprehensive comparison of > >> their relative merits discussed somewhere, but I have not been able to > >> find such a reference. Somehow the NuBus video cards we used to buy > >> managed this without using twice the video RAM. > > > >They managed this because the hardware has NEVER compensated for the > >vertical blanking. Programs had to compensate themselves. Games had to > >have a VBL interrupt handler running as part of their code which would > >tell them when the video blanking signal hit the top of the screen so they > >could know when to refresh the screen buffer. If a game didn't do this, > >you'd get the tearing you talk about. But it was never the video card's > >responsibility to prevent this tearing. > > Hmmm. Does that mean that the portions of the Tool Box which write > to the video space also have a VBL interrupt handler so that, e.g., > word processors won't cause screen tearing? That is, assuming that > word processors and such only use Tool Box routines to write to the > screen and never do so directly. > > >> Another question that interests me, but is not critical, is how to > >> implement QuickDraw accelleration. > > > >Apple used the Intel i860 in the 8*24GC to accelerate QuickDraw by porting > >most of the QD ToolBox to i860 assembly to run on the card instead of the > >CPU. I think lowendmac.com has a few articles on the 8*24GC, which from > >what I understand has a lot of compatability issues, especially with > >games. The Quadra on-board video circuitry was not accelerated, and was > >almost as fast as the 8*24GC, though it was optimized local bus video > >circuitry that took advantage of the 68040 architecture. Nonetheless, I > >would think a more compatible non-QuickDraw accelerated modern NuBus or > >PDS video card that's highly compatible with existing software would be > >more useful. > > The Quadra video probably gets a big boost through increased > bandwidth, I suspect. NuBus was great in its day, but it was 4 > bytes wide at 10 MHz with plenty of overhead per transaction. So > maximum total was 40 MB/s and real performance was considerably > lower. Hooking directly into the CPU's busses could double or > triple that since the memory/CPU bus typically ran at from 20 to 33 > or even 40 MHz. For example, the SE/30's PDS slot has a maximum > theoretical bandwidth of 64 MB/s because it is 4 bytes wide and runs > at 16 MHz. > > Nate, thank you for the great information. Do you have any idea how > the ToolBox routines were diverted to the video card? I assume that > the driver for the card must be loaded for this to work and some kind > of software patch is intercepting the relevant ToolBox calls, telling > the CPU to ignore them, and sending them to the video card, but I > have no idea how that is done. And I suspect that there would be > details, such as issues where the CPU gets too far ahead in execution > order if the video card is running behind. Perhaps they only > accelerate ToolBox calls which can't lead to those kinds of issues. > > I don't believe that QuickDraw acceleration must have compatibility > issues. I think the problem is likely that Apple just stopped > updating the drivers for the 8*24GC. For example, the Radius > Thunder 24/GT or Thunder IV GX family works fine up through about OS > 8.6 (and maybe later) with Quickdraw acceleration enabled and they > work in 030 to PowerPC machines without any hitches I've heard about. > > But in this case the compatibility required is fairly limited in > fact. I am concentrating solely on the SE/30. It would be nice to > build a NuBus video card someday, but I suspect that the limited > bandwidth in NuBus would make this a pointless exercise. We're > probably seeing close to the best that can be done with the last > Radius releases. I don't know that for a fact, but I suspect that it > is true. Especially because the Villagetronic MacPicasso 340 which > was released a year or two later than the Thunder IV GX has about the > same performance. > > Besides, if I ever finish the SE/30 video card project, the next > project will be to put an ethernet port on the thing. And if I ever > do that, the next project will be to put a USB port on the thing. > And if I ever do that the next project will be to put an IDE channel > on the thing... > > That's my fantasy. An SE/30 with grayscale display, a color display > out port, ethernet, able to connect to modern USB peripherals, and > sporting an internal notebook size IDE drive so that drive > availablility stops being an issue and heat and power requirements > are reduced.
Then wouldn't an easy beginning be making a multi-nubus-slot adapter for the SE/30 PDS? Then you could at least use normal NuBus video and network cards. Daan. -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
