Tuning aha1540 driver (ISC 2.2)

[WB3FFV]

>From article <LARRY.90Aug15125107 at focsys.uucp>, by larry at focsys.uucp (Larry Williamson):
> 
> My tests seem to indicate that the default values for BUSON, BUSOFF
> and DMASPEED are the fastest. 
> 
> With BUSON 5, BUSOFF 9 and DMASPEED 0; the system seems to be
> performing just fine. 

Have you tried to use any other settings?  Roy Neese at Adaptec strongly
recomended setting BUSON=7 and BUSOFF=4.  I would think increasing the 
BUSON time would be a BIG help.  I have heard of several people using a 
BUSON of 9 and a BUSOFF of 6, but haven't tried that on my side, as Roy's
recomendations seem to work great.

> I'm not entirely sure how to modify the DMASPEED parameter. Values of
> 0 and 1 seem to work, but 2 causes the system to enter the kernel
> debugger at boot time. I've not bothered trying a value of 3. How do
> these values relate to the DMA speeds of 5, 5.7, 6.7 and 8 Mhz that
> the controller is supposed to be able to support? Is it the obvious
> 0->5, 1->5.7, 2->6.7, 3->8?

Here are the various setting for the DMASPEED:

0 =	5.0  MBytes/sec
1 =	6.7  MBytes/sec
2 =	8.0  MBytes/sec
3 =	10.0 MBytes/sec
4 =	5.7  MBytes/sec

To find the highest possible setting you can use on your system, try using
the Bus Mastering Test which is located in ROM at location dc00:9


> The test bed system I'm using is an AMI MB with 4 Meg ram, 64K cache
> and 20 Mhz clock.

I placed a Adaptec 1542B controller in a 20mhz machine and have it running
at an 8mhz (DMASPEED=2) DMA rate, but this is highly system dependant.


> During these tests I've left the DMA speed selection header on the
> board open. This selects the default of 5 Mhz. I'm going to try
> other selections on the jumpers. Is there a reason why this is not a
> good idea?

This is the correct way to try it, but be sure to run the Bus Mastering 
Tests under MS/DOG in the ROM that I mentioned above.

> Any advise you can offer would be greatly appreciated. Thanks.
 Well there it is, the whole two cents worth!

> -Larry

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