From owner-freebsd-stable  Sun Mar 22 07:03:37 1998
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Date: Sun, 22 Mar 1998 10:01:29 -0500
From: Randall Hopper <rhh@ct.picker.com>
To: Joao Carlos Mendes Luis <jonny@coppe.ufrj.br>,
        Amancio Hasty <hasty@rah.star-gate.com>
Cc: multimedia@FreeBSD.ORG, stable@FreeBSD.ORG
Subject: Re: Fxtv vs Stable
Mail-Followup-To: Joao Carlos Mendes Luis <jonny@coppe.ufrj.br>,
	Amancio Hasty <hasty@rah.star-gate.com>, multimedia@freebsd.org,
	stable@FreeBSD.ORG
References: <199803220221.NAA18775@godzilla.zeta.org.au>
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Joao Carlos Mendes Luis:
 |//         /*  If TDEC is on, may be a while before old trash gets written on  */
 |//         if ( c->fps != c->fps_max )
 |//             memset( c->drv_buf, '\0',
 |//                     g.w * g.h * c->pix_geom_list[ c->pix_geom_idx ].Bpp );
 |
 |Why do you need to clear the buffer ?

I alluded to this in my last msg:

 |decimation is enabled.  At that time, it clears out the driver buffer so
 |that you don't see a stale last frame from the last capture up until the
 |first frame of the requested capture finally comes along.

"Fxtv" doesn't need to do it necessarily.  It just needs to be done.
Otherwise, the frame residing in the driver buffer for potentially up to a
full second will be the one from the last capture, potentially minutes or
hours old.  

A stale buffer is fine if app is processing the frame on interrupt, but
when it knows there's no way it can keep up, having signals issues 30X/sec
is pointless extra overhead just for bookkeeping the first frame.  Better
to just sample as fast as possible up to 30X/sec, and clear the buffer
before starting.

Randall

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