baxter@zola.ICS.UCI.EDU (Ira Baxter) (12/22/90)
I have had intermittent problems reading from an Everex EV833 tape drive subsystem under ISC 2.0.2 on a Micronics 20Mhz cache motherboard (MB). The symptom is that reading tens of megabytes of data eventually leads to a "PARITY ERROR DETECTED..." panic; otherwise the system is flawless. Even crazier is that the Everex-supplied DOS backup/restore tools will read hundreds of megabytes without problems. I run the tape controller configured to use DMA channel 1 as this is the default configuration suggested by Everex (the only other DMA device in this system is the floppy disk). I shipped the MB and the tape drive to Micronics because I suspected a MB problem; Micronics claims that after moving the tape drive to DMA3 that they see no problems. [They in fact have not tried the problem on DMA1, I think because they have a SCSI disk controller operating there]. A discussion with Everex's Unix/tape support guy says that Everex has been hearing of problems generically with tape drives operating DMA1 under ISC, but that the same drives operate DMA1 under SCO and other Unices without trouble. Is there truly a difference (other than channel number) between DMA1 and DMA3? [If so, WHY???] What does the ISC Unix Wangtek tape driver do differently when using DMA1 versus DMA3? [I suspect the answer is "nothing", but confirmation from a knowledgeable source at ISC would be welcome]. If the DMA channels are truly different, I'll be glad to move my DMA jumper and be rid of the problem. If not, moving the jumper does not constitute a convincing cure for the problem. IDB (714) 856-6693 ICS Dept/ UC Irvine, Irvine CA 92717