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Date: Sat, 16 Dec 1995 06:48:22 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199512151948.GAA28090@godzilla.zeta.org.au>
To: bde@zeta.org.au, nate@rocky.sri.MT.net
Subject: Re: sio overruns on 2.0.5R
Cc: FreeBSD-hackers@FreeBSD.org
Sender: owner-hackers@FreeBSD.org
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>> >> After I switched to a Asus P55TP4XE 90Mc I see things like
>> >> 
>> >> sio0: 5 more silo overflows (total 7)
>> 
>> >I hate to sound like a broken record, but are you *sure* you're using
>> >flow-control?  Can you use stty on the connected end to make sure?
>> 
>> Er, flow control has no effect on silo overflows.

>Really?  If a machine doesn't provide flow control can't you over-run
>the buffers if the machine gets loaded down and the interrupt load gets
>so bad that the sio interrupt handler isn't called enough.  However, if

If the interrupt load gets so bad that the sio interrupt handler isn't
called enough, then the interrupt handler won't get called enough to
control the flow.  This is for 8250-16550's; other chips are better.
Perhaps more importantly, the sender may not respond to the flow control
until many characters later, so either the reciever's hardware must have
enough buffering to hold that many characters, or the sio interrupt
handler must be called before the receiver's buffers fill up.

>you use flow control shouldn't it stop the buffer from getting
>overflowed simply because no more data is being received.

`silo' != `buffer'.  FLow control stops the 2 layers of buffers in the
driver from overflowing.  There is a different message for each layer.

Bruce