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Date:      Thu, 26 Mar 1998 10:22:51 +1100
From:      Bruce Evans <bde@zeta.org.au>
To:        ady@warpnet.ro, current@FreeBSD.ORG
Subject:   Re: silo overflows (Was Re: 3.0-RELEASE?)
Message-ID:  <199803252322.KAA29759@godzilla.zeta.org.au>

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> Likewise, here it is my experience with a CYCLADES Cyclom 16YeP multiport
>board & FreeBSD 3.0-971117-SNAP, both UP & SMP case (please nota that I 
>used the COM ports before installing the multiport board and did get zero 
>"silo overflow"s; also, setting speed to 115200 rather than 57600 makes
>the no. of overflows grow faster):

This problem is well known.  The PCI version of the cy driver doesn't
use fast interrupts, so at 115200 bps, it is likely to drop about N fifos
full of input whenever another driver preempts of masks cy interrupts for
N+0.5 msec.  The keyboard driver usually masks (non-fast) cy interrupts
for more than several msec to program the keyboard LEDs; PIO drivers
like the PIO wd driver can preempt (non-fast) interrupts for even longer
if the disk is fast and the controller is slow...

>----------
>Mar 25 19:46:01 ady /kernel: cy0: 1 more silo overflow (total 177)
>Mar 25 19:50:26 ady /kernel: cy0: 1 more silo overflow (total 178)
>Mar 25 19:50:58 ady /kernel: cy2: 1 more silo overflow (total 13)
>Mar 25 20:02:03 ady /kernel: cy0: 1 more silo overflow (total 179)
>Mar 25 20:03:11 ady /kernel: cy0: 1 more silo overflow (total 180)

It's doing well to get only one at a time :-).

Bruce

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