Tuning aha1540 driver (ISC 2.2)

Larry Williamson larry at focsys.uucp
Thu Aug 16 03:51:07 AEST 1990


A few weeks back (late june, I think) there was a thread here on
tuning the scsi driver for ISC Unix 2.2. I saved most of those
articles since we were planning on installing 1542A's on some machines
here.

I'm doing that now. 

My tests seem to indicate that the default values for BUSON, BUSOFF
and DMASPEED are the fastest. 

I've installed the Sync option jumper on the controller. 

With BUSON 5, BUSOFF 9 and DMASPEED 0; the system seems to be
performing just fine. 

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?

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

I'm bothered that if I modify these values in /etc/conf/cf.d/[ms]tune,
I get compiler warnings about these values being redefined. So I've
been modifying them in /usr/include/sys. I don't like this. What is
the normally accepted practice? Ignore the warnings? I hope not.

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?

Any advise you can offer would be greatly appreciated. Thanks.

-Larry



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