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GIC Acknowledge Register read has no impact

Sebastian Meisheit
Note: This was originally posted on 30th July 2012 at http://forums.arm.com

Hi,

Setup:
I am using Pandaboard ES with Cortex-A9MP (2x Cortex-A9) and connect to processor_0 by JTAG and Lauterbach hardware debugger.
From GICD_TYPER [10] = 1 i know the GIC implements Security Extensions.
From the Peripheral ID2 Register [7:4] = 1 i know its GICv1.
I am not able to enter Secure World (SMC or CPSR mode change doesnt work on the PandaES), so every access would be non-secure.

Problem:
According to the ICCIAR definition, an interrupt pending on a CPU interface should change from pending to active only after the register ICCIAR is read. In my GIC the interrupt changes immediately to active, if the priority is sufficient. I use the ICCIAR to get the current interrupt ID, but it has no efffect on the CPU interface or the GIC registers.
Is the ICCIAR definition wrong here, or am i missing something?

Greets
Sebastian
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  • Note: This was originally posted on 31st July 2012 at http://forums.arm.com

    Thanks for your thoughts!
    I found out it was human error once again. I watch memory around 0x48240100 (CPU Interrupt Interface registers sit here) while testing. And that means the debugger reads all the memory and thus memory mapped IO registers at that addresses.
    So by viewing the memory region, the IAR was read by the debugger :)
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  • Note: This was originally posted on 31st July 2012 at http://forums.arm.com

    Thanks for your thoughts!
    I found out it was human error once again. I watch memory around 0x48240100 (CPU Interrupt Interface registers sit here) while testing. And that means the debugger reads all the memory and thus memory mapped IO registers at that addresses.
    So by viewing the memory region, the IAR was read by the debugger :)
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