That's absolutely correct. I have an ISR in RTL 0.9J that's been getting an
interrupt once a second for several months without writing an EOI.
I also know from my AMX/MS-DOS experience that writing an extra non-specific
EOI to the PIC was a sure way to hang the computer. If you have to write an
EOI, make sure it's specific to the interrupt you're handling.
Also, IIRC, it's not the PIC that prevents higher priority interrupts from
interrupting lower priority interrupts, it's the CPU's interrupt-enable mask
bit (the one that's set and cleared with STI & CLI) that prevents them.
You might want to issue the equivalent of an STI to see if you can get the
behavior you want.
Norm
> -----Original Message-----
> From: daniel sheltraw [SMTP:[EMAIL PROTECTED]]
> Sent: Thursday, May 25, 2000 12:00 PM
> To: [EMAIL PROTECTED]
> Subject: RE: [rtl] FW: HELP --- IRQ Preemption
>
>
> Janet and Cyril
>
> I have been told (can't remember who) that it was not neccessary
> to write an EOI within the RT ISR. I am anxious to see how your question
> is
> resolved.
>
> Daniel
>
> >From: "Estabridis, Janet P" <[EMAIL PROTECTED]>
> >To: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>, "Estabridis, Janet P"
> ><[EMAIL PROTECTED]>, "'RT Linux Group'"
> <[EMAIL PROTECTED]>
> >Subject: RE: [rtl] FW: HELP --- IRQ Preemption
> >Date: Thu, 25 May 2000 06:14:51 -0700
> >
> >Cyril,
> >I tried that. I even found in the PIC data sheet that if you had 2
> >controllers, you needed to do the write twice. That did not work either.
> >Janet
> >
> >
> > > -----Original Message-----
> > > From: Briand Cyril [SMTP:[EMAIL PROTECTED]]
> > > Sent: Wednesday, May 24, 2000 10:27 PM
> > > To: 'Estabridis, Janet P'; 'RT Linux Group'
> > > Subject: RE: [rtl] FW: HELP --- IRQ Preemption
> > >
> > > Maybe you have to write to the PIC the EOI byte (outb(0x20, 0x20)) at
> >the
> > > beginning of your preemptable IRQ4 ISR code.
> > > Cyril.
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Estabridis, Janet P
> > > > Sent: Wednesday, May 24, 2000 6:46 AM
> > > > To: 'RT Linux Group'
> > > > Cc: 'Estabridis - Home'
> > > > Subject: HELP --- IRQ Preemption
> > > >
> > > > Hi,
> > > >
> > > > I'm using RTL V0.9J with 2.0.36.
> > > >
> > > > I have two ISRs in my embedded system. IRQ 3 and IRQ 4
> > > > I am monitoring how long I am in each ISR and what the preemption
> >looks
> > > > like by setting and clearing bits on the parallel port as I enter
> and
> > > exit
> > > > my ISRs. I monitor these lines with an o-scope.
> > > >
> > > > The highest priority ISR (irq 3) NEEDS to run at a very fixed rate
> so
> > > that
> > > > the ISR that grabs the data from the A/D converter FIFO does not
> > > overflow
> > > > causing loss of data. This ISR gets called every 1.6 msec and it
> >takes
> > > > approx. 550 usec to pull the data off.
> > > >
> > > > The lower priority ISR (irq 4) is an RS485 serial interface that is
> >used
> > > > at a lower rate (every 30 Hz, 33.33 msec). However, when it is time
>
> >for
> > > > this ISR to send it's 6 bytes of info it takes approx. 600 usec to
> do
> > > so.
> > > >
> > > > What I expected to see on the o-scope because of the priorities of
> the
> > > > IRQ's is that the lower priority ISR would be preempted when the
> >higher
> > > > priority ISR needed service. BUT this DOES NOT happen and I lose
> data
> > > !!!
> > > >
> > > > I know a simple microcontroller can provide this desired timing
> > > > situation...
> > > >
> > > > I have tried numerous things,
> > > >
> > > > * Writing to the PIC directly to hopefully allow IRQ 4 to be
> preempted
> > > > (outb commands)
> > > > * Using a non-rt Slow ISR as described in Rubini's Device
> Drivers
> > > >
> > > > I have not tried
> > > > * Bottom half ISR as explained in Rubini's book
> > > >
> > > >
> > > > Does anyone out there have experience with this and can tell me
> >EXACTLY
> > > > what I can do?
> > > > Does anyone know if I CAN or CANNOT accomplish this scenario?
> > > >
> > > > Thanks in advance --
> > > >
> > > > Janet Estabridis
> > > > Electrical Engineer
> > > > NAWC Code 473E00D
> > > > Building 31440 Room 1017
> > > > China Lake, CA 93555
> > > > [EMAIL PROTECTED]
> > > > (760) 939-2896 FAX (760) 939 -3075
> > > >
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> >
>
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