Architectures and Processors forum R5 MPU Background Region

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R5 MPU Background Region

Offline ijahmad 10 months ago

I have a follow-up question from this.

I want to create a 4GB background region on R5 core. All I have to do is to fill following for region-0 in MPU?

starting address: 0

size: 2^32 = 0x100000000

Is anything else I need to do to declare a background region?

-ijaz

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Offline Martin Weidmann 10 months ago in reply to ijahmad +2 verified

Register value of 0x3F => b0011_1111 Dividing that into the fields: bit[0] = enable = b1 = Enabled bits[5:1] = RSize = b 11111 = 31 If you take a look at the description of RSize in the Armv7-A...

0 Offline Martin Weidmann 10 months ago
You'll need to program

DRBAR with the starting address (so 0x0)

DRSR with the size, enable and sub-regions

Remember that the size field is 2^(N+1), and shifted by 1 position due to the Enable field. So a 4GB region, with no sub-regions), would be 0x0000_003F

DRACR with the settings (e.g. cacheable, read/write)
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0 Offline ijahmad 10 months ago in reply to Martin Weidmann

Hi Martin Weidmann,

Thanks for the reply, how 2^(N+1) = 0x0000_003F (sub-region, size, enable). N=32 isn't it?
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+1 Offline Martin Weidmann 10 months ago in reply to ijahmad

Register value of 0x3F => b0011_1111

Dividing that into the fields:

bit[0] = enable = b1 = Enabled
bits[5:1] = RSize = b11111 = 31

If you take a look at the description of RSize in the Armv7-A/R Architecture Reference Manual (Rev C.d, page 2720) it says "region size is 2^(N+1) bytes." (Where N is the value of the field)

So 2^(31+1) = 4GB.
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0 Offline ijahmad 10 months ago in reply to Martin Weidmann

Perfectly answered.

Thanks
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