Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!gatech!purdue!ames!amdcad!light!bvs
From: bvs@light.uucp (Bakul Shah)
Newsgroups: comp.unix.questions
Subject: Re: Code 0x01 in Tatu Ylonen SCSI driver
Keywords: synchronous transfer
Message-ID: <1989Aug5.144627.11225@light.uucp>
Date: 5 Aug 89 21:46:24 GMT
References: <1670@apt.UUCP>
Reply-To: bvs@light.UUCP (Bakul Shah)
Distribution: na
Organization: Bit Blocks, Inc.
Lines: 44

In article <1670@apt.UUCP> brian@apt.UUCP (Brian Litzinger) writes:
> ...
>However, I recently connected a Fujitsu M2249/SA drive and
>I've come across a message from the drive that Mr. Ylonen's
>driver doesn't handle.
>
>I regularly get the message:
>
>scsi: unknown message received from drive 2: 0x1

Most likely this is a synchronous transfer message.  The way
to handle this is to get rest of the message, make sure it is
a sync. xfer msg and send an sync. xfer msg back in response.
If your hardware can't handle sync. xfer, send a MESSAGE REJECT
(0x7), if it can, send a sync. msg.

Format of a sync.msg:

	{       0x1,    /* extended message */
		0x3,    /* size of the message */
		0x1,    /* sync xfer */
		PERIOD, /* in multiples of 4 ns -- REQ/ACK period */
		OFFSET, /* number of times REQ can be ahead of ACK */
	}

Set PERIOD to max(how fast you can xfer bytes, period in
target's msg).  Set OFFSET to 0 for async transfer or to
min(your max offset, offset in target's msg).  You will have
to tell your hardware you are doing sync. xfer.  It would be
easy to whip up the right code but I don't have this driver.

Either side can send this message so if your h/w can handle
sync. xfer, you too can send this message to find out if a drive
handles sync. xfer.

I suspect your driver does not handle unexpected messages very
well.  If it receives a message it doesn't understand, it should
send back a MESSAGE REJECT and continue.

For more details read the SCSI standard (ANSI X3.131-1986).
(Computer Literacy in Santa Clara had a few copies a while
back).  It is quite readable (unusual for a standard :-)

-- Bakul Shah <..!{ames,sun,ucbvax,uunet}!amdcad!light!bvs>