From mboxrd@z Thu Jan  1 00:00:00 1970
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In-Reply-To: <20050325183606.GA93332@smp500.sitetronics.com>
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	<20050325183606.GA93332@smp500.sitetronics.com>
Date: Fri, 25 Mar 2005 18:22:51 -0600
Subject: Re: [9fans] tsleep / timer questions
From: vdharani@infernopark.com
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
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> Related to my work writing a driver for the Ziatech ZT5503 SBC
> watchdogs, I've come up with a question.
>
> Obviously the watchdog needs to be `strobed' at some interval to
> keep it from resetting the machine (after it has been enabled).
> I'm having troubles figuring out how to do this.
>
> Taking a look at the driver for the Ziatech 5512 watchdog that
> Eric Van Hensbergen write for Inferno, I see that he's making
> use of addclock0link(), which makes sense. This seems to be
> overkill for my needs though. I'm not sure the resolution of the
> timer on the ZT5512 blades, but mine have a minimum resolution
> of 250ms, which means that they'd be strobed twice in their
> timeout period.
>
> That's not so bad, but some of the other resolutions (the timer
> supports 250ms, 500ms, 1s, 8s, 32s, 64s, 128s and 256s
> intervals), this can get to be an issue. I personally have no
> use for the 256s resolution, and I'm sure I'm the only person on
> the planet running Plan 9 on these blades, but I'd really like
> to have a driver that's not overkill.
>
> So, I thought a nifty solution would be to make use of the
> rendezvous stuff and call tsleep. But I don't understand how
> this should work. When the watchdog is enabled, I need to start
> some procedure that never returns. This would be easy in
> userland, where I could simply start another thread, but how do
> I do this in-kernel. If I've read in /dev/watchdog
>
> enable resolution 500ms
>
> and I've parsed that, how do I then call the procedure to do the
> timer?
>
> My procedure looked like (until I realized that it'd
> never work if I understand the behavior correctly, which I'm
> fairly certain I do):
>
> void
> watchdog_strobe(void)
> {
> 	for(;;) {
> 		if (!enabled)
> 			break;
>
> 		tsleep(wd_timer, return0, nil, wd_resolution);
> 		inb(IOP_Watchdog); /* Reading the IO port strobes the WD */
> 	}
> }
>
> So I'm stuck with the problem: how do I enable a separate timer?
>
> Hope the question is clear.

first, i hope i understood your question corectly. second, i use inferno
mostly but i guess this will do the trick in plan9 as well. i dont have
access to plan9 system next to me to check this.

kproc() starts a new kernel process starting from the function you pass.
so, you will call kproc with watchdog_strobe as the argument. kproc()
starts the process and returns immediately. you need to modify
watchdog_strobe function as needed by kproc().

hope this helps.

thanks
dharani