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From: roger@mips.UUCP (Roger March)
Newsgroups: comp.unix.wizards
Subject: Device driver timeout question ...
Message-ID: <570@obiwan.UUCP>
Date: Wed, 5-Aug-87 12:08:13 EDT
Article-I.D.: obiwan.570
Posted: Wed Aug  5 12:08:13 1987
Date-Received: Tue, 18-Aug-87 03:01:40 EDT
Lines: 33
Keywords: device driver, timeouts, sick devices


	  A friend (yeah, sure), no really, a friend of mine is trying
	to patch up this device driver and foolishly came to me for help,
	so now I'm asking you. It is a block device and locks up when the
	cable isn't connected or people chew on the power cords, well at
	least when the cable isn't connected. I suspect that the lack of
	a cable means the DMA never starts and most certainly the device
	driver will never get an interrupt from the controller. It seemed
	to me that a possible solution was:

	1)	Enter the "strategy" routine and set up the DMA. Also set
		a "timeout" for N minutes. Wait for 2) or 3).

	2)	On a timeout, print a horrible error message and try to
		clean things up.

	3)	On a DMA complete interrupt, indicate that when the timeout
		occurs you were just kidding and everything is really okay.

	The above does some nasty stuff now when the cable is connected.
	Since the "timeout" is for N minutes, and requests to the device can
	be much quicker than this, it looks like I can expect to have several
	outstanding "timeout"s working; one of which may be valid.
	  So (finally) my question is: is there a way to kill outstanding an
	"timeout" when realize it is no longer neccessary? If not, is there
	a limit to how many "timeout"s can be issued before some buffer in
	the kernal fills? Or, is my algorithm totally brain damaged and I
	should go back to writting AI programs for microprocessor controlled
	toasters? Thanks.
-- 
-Rogue Monster
UUCP: {decvax,ucbvax,ihnp4}!decwrl!mips!roger  OR  roger@mips.com
USPS: MIPS Computer Systems, 930 Arques, Sunnyvale, CA 94086, (408) 991-0220