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Message-ID: <001301bfaebe$5717cca0$a44b8486@jking>
From: "Jim King" <king@sstar.com>
To: <e-masson@kisoft-services.com>
Cc: <freebsd-stable@FreeBSD.ORG>
References: <5564.000424@pd.chel.ru><20000424114057.A692@pir.net><14596.37283.563515.214828@localhost.nantes.kisoft-services.com><003801bfae25$39a6d100$a44b8486@jking> <14597.37879.611136.906144@localhost.nantes.kisoft-services.com>
Subject: Re: sio interrupt handler problem
Date: Tue, 25 Apr 2000 08:58:23 -0500
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----- Original Message -----
From: "Eric Masson" <e-masson@kisoft-services.com>
To: "Jim King" <king@sstar.com>
Cc: <freebsd-stable@FreeBSD.ORG>
Sent: Tuesday, April 25, 2000 7:47 AM
Subject: Re: sio interrupt handler problem

On Tuesday, April 25, 2000 7:47 AM, Eric Masson wrote:
> Jim King writes:
> >One thing I've done in the past to overcome serial port problems is to
patch
> >sys/isa/sio.c to set the FIFO receive trigger level to 8 bytes instead of
14
> >(FIFO_RX_MEDH instead of FIFO_RX_HIGH).  If you have a piece of hardware
or
> >a misbehaved driver that's causing high interrupt latency this change be
> >really beneficial, and greatly outweighs the higher interrupt overhead
when
> >using an 8 byte trigger.
> >
> ><soapbox>
> >An 8 byte trigger is a safer option that causes better operation on weird
> >hardware without signifcantly changing anything on good hardware.  I
really
> >wish sio.c would be changed to set the trigger to 8 bytes by default, or
at
> >least have a flags option to change the trigger level.
> ></soapbox>
>
> I applied the following crappy patch to sio.c, and i still encounter the
> SOs
>
> *** /sys/isa/sio.c.ORIGINAL Tue Apr 25 14:15:06 2000
> --- /sys/isa/sio.c Tue Apr 25 14:15:34 2000
> ***************
> *** 1113,1119 ****
>   com->tx_fifo_size = 32;
>   printf(" ST16650A");
>   } else {
> ! com->tx_fifo_size = COM_FIFOSIZE(flags);
>   printf(" 16550A");
>   }
>   }
> --- 1113,1119 ----
>   com->tx_fifo_size = 32;
>   printf(" ST16650A");
>   } else {
> ! com->tx_fifo_size = 8;
>   printf(" 16550A");
>   }
>   }
>
>
> sio0 at port 0x3f8-0x3ff irq 4 flags 0x10 on isa0
> sio0: type 16550A lookalike with 8 bytes FIFO
>

> sio0: 1 more silo overflow (total 1)
> sio0: 1 more silo overflow (total 2)
> sio0: 1 more silo overflow (total 3)
> sio0: 2 more silo overflows (total 5)
> sio0: 1 more silo overflow (total 6)
> sio0: 1 more silo overflow (total 7)
> sio0: 2 more silo overflows (total 9)
> sio0: 2 more silo overflows (total 11)
> sio0: 1 more silo overflow (total 12)
> sio0: 1 more silo overflow (total 13)
> sio0: 1 more silo overflow (total 14)
> sio0: 2 more silo overflows (total 16)
>
> Did I understand your point ? (Kernel patching isn't part of my daily work
> :).

You need to patch the code that sets the FIFO receive trigger level.  I
think all you did was change the number that gets printed when the port is
probed. :-(

Look for a line like:
    com->fifo_image = t->c_ospeed <= 4800 ? FIFO_ENABLE : FIFO_ENABLE |
FIFO_RX_HIGH;

Change the "FIFO_RX_HIGH" to "FIFO_RX_MEDH".

Jim




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