33014-18@sjsumcs.sjsu.edu (Eduardo Horvath) (12/06/89)
Just as I thought that the argument over whether DMA is good was finally
settled I came up with a nasty rumor. Tryning to remember exacly what was
said last night:
Is there a bug with the Amiga DMA scheme that causes data to be lost
under some obcure conditions, or is that somebody mis-reading
a 2090 review again?
At the very least I would like to have enough ammunition to stamp out
any nasty little rumors like this before they start, unless they are accurate,
in which case theyshould be documented.
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Eduardo Horvath | 33014-18@sjsumcs.SJSU.EDU | IMI - International Microsystems
"Why don't you stop your whining, and get back to work!"
- Doctor Scienceccplumb@rose.waterloo.edu (Colin Plumb) (12/08/89)
In article <1989Dec6.151618.3097@sjsumcs.sjsu.edu> 33014-18@sjsumcs.SJSU.EDU (Eduardo Horvath) writes: > Is there a bug with the Amiga DMA scheme that causes data to be lost > under some obcure conditions, or is that somebody mis-reading > a 2090 review again? Sigh... There is no bug in the Amiga's DMA scheme. There is a bug in the 2090 that causes it to drop bytes when there is severe memory contention (such as DMA into chip memory with 4-bitplane high-res screens), but it detects this condition and retries. The 2090 bug does not cause lost data, only enormous numbers of retries. The details are that the 2090 does not do anything with the "buffer full" indicator on its FIFO... it naively assumes the buffer can be flushed to memory faster than the disk reads. So it keeps asking the disk for data even though it can't accept it. This causes problems. -- -Colin