topic Re: XEP100 - MPU Descriptors granularity in S12 / MagniV Microcontrollers

XEP100 - MPU Descriptors granularity

Pedro_ — Wed, 21 Jan 2009 21:36:45 GMT

Hi all,

there's something about the granularity of the Memory Protection Unit descriptors that is not clear to me.

Let say I have a section of data starting at 0x13F800 and ending at 0x13F88F

Because of the 8 byte granularity, the actual addresses loaded in the descriptors would be:

Start - 0x13F800

End - 0x13F888

So, when accssing addresses between 0x13F889 and 0x13F88F, would that be a protection violation?

It doesn't seem to be so I thought I'd double check with you ..

Thanks

Re: XEP100 - MPU Descriptors granularity

MJW — Wed, 21 Jan 2009 22:30:25 GMT

Hello Pedro_,

no, it would not be a protection violation for accesses within the 0x13F889..0x13F88F range.

The address configuration bits in the MPU descriptors which cannot be set due to granularity are internally treated like this:

Lower Boundary addresses are right-appended with zeroes.
Upper Boundary addresses are right-appended with ones.

So, for example, if you do this:

Start = 0
End = 0

you get the range 0..7.

MJW

Re: XEP100 - MPU Descriptors granularity

Pedro_ — Wed, 21 Jan 2009 23:07:12 GMT

Thanks for your answer MJW