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From: Archie Cobbs <archie@whistle.com>
Message-Id: <199812042043.MAA06772@bubba.whistle.com>
Subject: Re: Help with clist_alloc_cblocks()
In-Reply-To: <199812042040.MAA08017@root.com> from David Greenman at "Dec 4, 98 12:40:06 pm"
To: dg@root.com
Date: Fri, 4 Dec 1998 12:43:04 -0800 (PST)
Cc: freebsd-hackers@FreeBSD.ORG
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David Greenman writes:
> >I'm trying to write a line discipline, roughly similar to the PPP
> >line discipline. My question is, what are the correct parameters to
> >give to clist_alloc_cblocks()?
> >
> >  /*
> >   * Pre-allocate cblocks to the an appropriate amount.
> >   */
> >
> >    ttyflush(tp, FREAD | FWRITE);
> >    clist_alloc_cblocks(&tp->t_canq, 0, 0);
> >    clist_alloc_cblocks(&tp->t_rawq, 0, 0); 	/* XXX probably wrong! */
> >    clist_alloc_cblocks(&tp->t_outq, MLEN + NGT_HIWATER, MLEN + NGT_HIWATER);
> >
> >I'm not sure how to determine what the correct values to call
> >clist_alloc_cblocks() should be. The values I'm using now cause a
> >bunch of "interrupt-level buffer overflows" reported from the sio
> >driver. It looks like I can simply increase the values for tp->t_rawq
> >but I'd like to understand exactly what they mean first.
> 
>    A lack of cblocks should not cause interrupt-level buffer overflows.

Hmm, then that assumption is wrong. Do you have any suggestions
as to (a) what the problem indicates and/or (b) how to fix it?

We're running at 230K (the serial chip supports this speed).
This doesn't happen at 115K, so clearly something is overflowing
somewhere because characters are arriving too fast.

Is this some kind of fundamental limitation of the hardware
or is there a way to address it in software by increasing the
size of some buffer somewhere?

Thanks,
-Archie

___________________________________________________________________________
Archie Cobbs   *   Whistle Communications, Inc.  *   http://www.whistle.com

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