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Re: [PATCH] hw/timer/a9gtimer: Clear pending interrupt, after the clear

From: Václav Vanc
Subject: Re: [PATCH] hw/timer/a9gtimer: Clear pending interrupt, after the clear of Event flag
Date: Thu, 9 Jul 2020 14:16:12 +0200

On 6/26/20 4:46 PM, Peter Maydell wrote:
On Tue, 16 Jun 2020 at 08:04, Václav Vanc <vav@sysgo.com> wrote:

On 6/15/20 1:04 PM, Peter Maydell wrote:
We must distinguish between two cases:
1, Auto-increment is disabled.
I just run some test on SABRE Lite (i.MX6) board.
I had auto-increment disabled, I verified, that GIC is configured for
Edge interrupts. Once count went past the compare value I got the
interrupt. I did not touch Timer registers, just signal EOI to GIC and
surprisingly, I got a another interrupt. If I stopped the timer
interrupts stopped coming (Status was still set to 1).

  From this behavior I assume, that every time the Timer is incremented
(and Timer value is past the compare value) an EDGE interrupt (that
means actual X->0->1 transition) is asserted. This is really interesting
from HW point of view. This would mean, that a9_gtimer_update function
should generate the pulse and not level on compare event.

That's interesting. Which version of the Cortex-A9 does this
board have? The TRM documents that the comparator behaviour
changed in r2p0...

-- PMM

It is "SABRE Lite (i.MX6)" board with Cortex-A9 r2p10.
Behavior is also the same for "Xilinx Zynq-7000 SoC ZC702 Evaluation Kit" with Cortex-A9 r3p0.

Unfortunately I do not have any board with older revision of Cortex-A9.

Best Regards,
Ing. Václav Vanc
Project Engineer

SYSGO s.r.o.
Embedding Innovations
Research and Development Center Prague
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E-mail: vaclav.vanc@sysgo.com

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