riscy
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Re: Should we have SCSI?

To: riscy@pyramid.com
Subject: Re: Should we have SCSI?
From: Drew Eckhardt <drew@nag.cs.Colorado.EDU>
Date: Tue, 06 Jul 1993 14:33:07 -0600
In-reply-to: Your message of "Tue, 06 Jul 1993 14:57:52 MDT." <9307061957.AA10528@ubitrex.mb.ca>
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
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    > SCSI on the motherboard:
    
    > For those wanting SCSI, the motherboard wins hands down.
    
    I definitely agree.  And the proliferation of CD-ROM is
    going to make SCSI more desirable through the next 3-5 years.
    
    The part could be socketed, though PLCC sockets drive me up
    the wall around here with unreliable connections.  
    
    There are a number of SCSI controller chips worth looking
    at, including the NCR 5380 and derivatives (including the
    NatSemi DP8490) and the Western Digital 33c93 and derivatives.

    I would tend towards the 5380 type, as they are multiple sourced
    (cheap), well-known (Seagate ST-01), and can provide reasonable
    performance.  

Nope.

I wrote the Linux Seagate ST-01 (ie, with the Nat. Semi part) driver, and 
I would avoid this part like the plague.  The designer obviously failed his 
introductory digital circuits class where they taught FSM design, because
the chip can't tell you when the SCSI REQ line transitioned low->high,
only when it's currently high.  Faster SCSI devices work OK if you 
just sit in a tight loop and blindly write to the port, with slower
SCSI devices, you have to loop, wait for it to go low then high, and 
be sure to timeout because you'll miss it a lot.  The chip can only 
generate an interrupt when the SCSI SEL line is raised, so most of the 
time you sit arround spinning your wheels in a loop (and you can't 
DMA to it because you need to make sure the status registers have the 
right values)

IMHO, the 53cf90 series is the best choice I've seen so far, I don't
know about the Western Digital chip, but it rings a bell as the chip
used in the WD7000 controller.

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