ARMv8 Foundation Model: writing to switches and leds

Hi everyone,

as I asked on http://stackoverflow.com/questions/25907502/armv8-foundation-model-switches-and-leds, I am trying to write

a value to the "switches" and "leds" register of the Foundation Model, to get some feedback (I've got some UART issues to debug).

All attemps to write to these registers are failing, even just after boot at EL3 in 64 bits mode.

I recently discovered that I got a synchronous exception classified  as External.

ESR_EL3 is 0x96000250 (Exception class 0x250, Data Abort, IL is 32 bits and ISS explains that a external abort on write has occured).

ARM's user manual for the model specifies that these registers are R/W registers. Did I miss something to be able to modify them by software ?

Best,

Vincent

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  • Hi Vincent,

    Sorry we have not seen your question earlier.

    What is the exact address that is triggering the abort?

    It should be contained in the FAR_EL3 register.

    Can you also try with a STR instruction instead of STRB?

    It seems the SysReg component only accepts 32 bits aligned write, I am not sure why the reads would behave differently.

    Edit: Can you also confirm which version of the Foundation model you are using (--version)?

    Also what is the command line you are using to start the model?

    Regards,

    Simon

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  • Hi Vincent,

    Sorry we have not seen your question earlier.

    What is the exact address that is triggering the abort?

    It should be contained in the FAR_EL3 register.

    Can you also try with a STR instruction instead of STRB?

    It seems the SysReg component only accepts 32 bits aligned write, I am not sure why the reads would behave differently.

    Edit: Can you also confirm which version of the Foundation model you are using (--version)?

    Also what is the command line you are using to start the model?

    Regards,

    Simon

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