withers@nitmoi.enet.dec.com (George Withers) (03/12/91)
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I recently purchased an ASDG/Micron 2Mb memory board and
installed it in my A2000 (old Agnus, rev 4.4 motherboard, A2090A
SCSI controller). It procededed to trash a partition of my drive
when it was accessed even though the memory was there according
to AVAIL.
I was told by someone that the same thing happened to them on
a Rev 4.3 motherboard and that they had to do the "pull-up U605"
fix given in "The Flake Report". When I told them I had the faster
U605/U602 buffer chips (74ALSmumble) they said that should have
fixed it.
So, can someone give me an idea of what I can do? The person who
had the problem before says it happened consistently to him on
DMA's from memory to disk. That would jibe with what I was doing
as it crashed running PasTeX, where PasTeX was reconfigured to
be using large amounts of memory.
Thanks in advance for any and all help,
George
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George Withers, Jr. | "There is no life I know to compare
Digital Equipment Corp., 97 Piper Road | with pure imagination. Living
Acton, MA 01720 AT&T: 508.264.2339 | there you'll be free .. if you
Addr: withers@nitmoi.enet.dec.com | truly wish to be." - W. Wonka
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DISCLAIMER: "Don't look at me! I didn't do it!" (Krusty the Clown)daveh@cbmvax.commodore.com (Dave Haynie) (03/13/91)
In article <21002@shlump.nac.dec.com> withers@nitmoi.enet.dec.com (George Withers) writes: >====================================================== > >I recently purchased an ASDG/Micron 2Mb memory board [which] procededed to >trash a partition of my drive when it was accessed even though the memory was >there according to AVAIL. >I was told by someone that the same thing happened to them on a Rev 4.3 >motherboard and that they had to do the "pull-up U605" >So, can someone give me an idea of what I can do? The person who had the >problem before says it happened consistently to him on DMA's from memory to >disk. The mentioned "U605 pullup" does cure one potential problem that relates to DMA activity. The A2000 bus uses several pullup resistors to hold the bus in a quiescent state during a bus handoff (one master gets off, then the next one gets on). The problem is that, in conjunction with on brand of 74ALS245, we have seen that the BAS* (Bus Address Strobe) line sometimes takes too long to get pulled up by the supplied pullups on Rev 4.4 and earlier A2000s. The only problem we have recorded at Commodore in relation to this is in conjunction with DMA to coprocessor card memory. The A2630, for example, has a much faster memory system than a typical Amiga device. After a bus handoff, it can get back on the bus and see the slowly rising BAS* as logically asserted just long enough to start a memory cycle. Traditional 7MHz devices like Chip RAM and most memory cards don't get into a memory cycle soon enough for this to be a problem, even on those systems which fully exhibit the problem. It certainly is not impossible for a Zorro II memory card to be sensitive to this problem, however, and wouldn't be saying anything bad about that card, it's just very unlikely. The fix is simple. It requires the addition of a 1K pullup resistor between pins 11 and 20 of U605, which is a 74ALS245 chip found in-between the Coprocessor and first Zorro II slot on the A2000. There's no reason to have this fix done if you're not having a problem -- as I mentioned, it has to date only been observed with one brand of ALS245. On the other hand, there's no reason not to do it if it'll make you feel better, or if there's a problem that might be related to this, since it's a perfectly acceptible fix, and became part of standard production on all A2000s as of Rev 4.5. > George Withers, Jr. | "There is no life I know to compare -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "What works for me might work for you" -Jimmy Buffett