Exclusive Access Restriction Clarification

Hi,

The description in the Spec is a little vague on this. The requirements for a pair exclusive access are same id, same length, transaction can't be cacheable and control signals must be identical. Does this imply AWPROT and ARPROT have to be same for EA read and EA write? What if the AWPROT and ARPROT are different, should the device should return OKAY instead of EXOAKY?

Does anyone out there have any comments on this?

Thanks,

Ting

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  • Hi Ting,

    I'm not sure on the requirements for all of the bits, but I strongly suspect that you would want them to be identical. The AR/WPROT[2] bit proves the isolation signals for the Security Extensions (a.k.a. TrustZone in the ARM products) so if those bits differ it is highly likely that the slave will treat them as totally separate accesses (or reject one of them). In some implementations transactions with different PROT[2] bits may even get sent to totally different slaves ...

    HTH,

    Pete

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