486 Speed (or lack thereof...)

[neese at adaptex.UUCP]

>/* ---------- "486 Speed (or lack thereof...)" ---------- */
>Summary: my shiny new 25Mhz 486/ISC/1542A system is not very fast :-(
>
>Configuration: Elite Group 486 motherboard 8Mb 80nS RAM
>               Adaptec 1542A (Version 3.07)
>               Micropolis SCSI 380 Mb Drive.
>               AMI BIOS (486 v1.1 042790)
>               Oak VGA Card (came with the box!)
>
>Problems:  Firstly, if I set the DMA speed to over 5Mb the system
>crashes with On Board Parity Error when accessing the 1542.  Addresses
>reported vary from 0x1954 ot 0x8478.  Any Ideas??  I assume that this
>message is from the BIOS but I don't know that - does the Adaptec
>generate such messages?

The parity error message is generated from the system BIOS rom.

>Is this the Adaptec or the Motherboard or the Chipset settings?  The board
>docs say it is rated for 8Mb DMA.

The error is caused by the mother board design.  There are three areas that
could cause this error.  1) If the motherboard memory logic, as provided
on the AT bus, has been artificially slowed down, then this error may occur.
2)  If IOCHRDY has not been implemented correctly this error could be shown.
Overdriving IOCHRDY will slow down the 154x faster than anything.
3)  The VGA card may be the culprit as well.  Video cards have memory that
the system must address.  If the memory design of the video card is such that
it requires very long memory signals to work poperly, then this would slow
down the 154x adapter as well.  Especially if the manufacturer has taken
this into account and has done 1).

>Speed:  When running with the DMA speed at 5Mb the beasty is not
>significantly faster than my Altos Series 1000 (16Mhz 386 & SCSI).

Have you tried adding the synchronous jumper to the 154x board?  This would
help throughput.  Is the Micropolis read ahead enabled?

			Roy Neese
			Adaptec Senior SCSI Applications Engineer
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