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