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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