daveh@cbmvax.UUCP (Dave Haynie) (10/21/88)
in article <1335@unisoft.UUCP>, paul@unisoft.UUCP (n) says: > In article <5025@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes: >>Interrupt line to each slot. Standard NuBus interrupts are weird; the board >>issuing the interrupt becomes the bus master and bangs on a chunk of memory >>that belongs to the board it wishes to interrupt. This does make sense in >>a system of multiple masters, but not so much on something like a Mac II.. > Actually the problem is more the amount of board real-estate required to > make a board that is a master, you have to add a couple of extra state machines, > arbitration logic, drivers for the address lines etc etc it was really a > good idea to just provide a pin you yank low when you want to signal an > interrupt ..... my minimal slave logic is normally around 6 chips ... Sure enough, especially now that Mac NuBus uses boards so much smaller than the original Eurocard. I'm sure the whole point of NMI was to make it easier for a board to generate interrupts; these are basically the same idea now as the interrupts you can generate on an IBM or Amiga bus. But the whole idea of an NMI per slot doesn't make sense unless you have something you can call a default master, like on the Mac II. Despite the heavy duty overhead of master-driven interrupts on NuBus, they are an elegant solution to the problem of who-get-the-interrupt in a system with multiple and equivalent masters. Like lots of NuBus stuff; pretty elegant, not quite so practical in many applications. >>The NeXT machine changes the NuBus clock from 10MHz to 25MHz, and the bus >>drivers from Bipolar to CMOS. That should be sufficient to render it >>incompatible with any existing NuBus cards. > yes I agree, if it weren't for this I think all my cards would run simply > by replacing the PALs with faster parts (and with more internal wait states - > isn't programmable logic great). Yeah, but now maybe you need more states. Of course, all those 20R8s can now be changed to 22V10s or maybe something with more internal state, so you still get pin compatibility. I do love this programmable logic -- my latest project uses 14 PALs, though I wish they'd hurry up and get this 7.5ns stuff available in quantity... > This will probably mean that the base prices of cards will be higher - > also since the volumes will be low for quite a while, I too don't expect > a mad rush of 3rd parties (from outside Higher Ed at least) designing > hardware for it. > Paul That's pretty much what I figured. Though one thing we've found with Amiga machines is that you can get higher education folks who'll do lots of interesting hardware that may not have the immediate commercial application that'll interest a commercial 3rd party in doing it. Of course, it's also got to be a hardware system a relatively small group can easily design for. Not being a NuBus designer, it's good to hear that all my conjectures weren't out of line. > Paul Campbell, UniSoft Corp. 6121 Hollis, Emeryville, Ca ..ucbvax!unisoft!paul -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy "I can't relax, 'cause I'm a Boinger!"