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Date: Fri, 27 Feb 2004 08:45:28 -0500 (EST)
From: "Richard B. Johnson" <root@chaos.analogic.com>
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To: Michael Frank <mhf@linuxmail.org>
cc: Russell King <rmk+lkml@arm.linux.org.uk>,
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       "Grover, Andrew" <andrew.grover@intel.com>,
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       Tim Bird <tim.bird@am.sony.com>,
       Linux Kernel list <linux-kernel@vger.kernel.org>
Subject: Re: Why no interrupt priorities?
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On Fri, 27 Feb 2004, Michael Frank wrote:

> On Fri, 27 Feb 2004 09:05:48 +0000, Russell King <rmk+lkml@arm.linux.org.uk> wrote:
>
> > On Fri, Feb 27, 2004 at 02:26:31PM +0800, Michael Frank wrote:
> >> Is this to imply that edge triggered shared interrupts are used anywhere?
> >
> > It is (or used to be) rather common with serial ports.  Remember that
> > COM1 and COM3 were both defined to use IRQ4 and COM2 and COM4 to use
> > IRQ3.
> >
> >> Never occured to me to use shared IRQ's edge triggered as this mode
> >> _cannot_ work reliably for HW limitations.
> >
> > The serial driver takes great care with this - when we service such an
> > interrupt, we keep going until we have scanned all the devices until
> > such time that we can say "all devices are no longer signalling an
> > interrupt".
> >
> > This is something it has always done - it's nothing new.
> >
>
> Sorry, i think the serial driver IRQ is level triggered :)

           CPU0       CPU1
  0:    7904936    7922491    IO-APIC-edge  timer
  1:      74277      70096    IO-APIC-edge  keyboard
  2:          0          0          XT-PIC  cascade
  3:        535        556    IO-APIC-edge  serial <--- EDGE
  4:          2          1    IO-APIC-edge  serial <--- EDGE
 10:    3435637    3440251   IO-APIC-level  eth0
 11:     295018     296838   IO-APIC-level  BusLogic BT-958
 13:       4567       4591   IO-APIC-level  Analogic(tm) AMX/AFF Driver
 14:       1331       1239   IO-APIC-level  Analogic(tm) DSP/DSS Driver
 15:          2          3   IO-APIC-level  Analogic(tm) VXI/MSG Driver
NMI:          0          0
LOC:   15826338   15826337
ERR:          0
MIS:          2

Cheers,
Dick Johnson
Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips).
            Note 96.31% of all statistics are fiction.