how to understand powerpc's BRx ORx

Baurzhan Ismagulov ibr at
Mon Sep 13 07:08:27 EST 2010

On Fri, Sep 10, 2010 at 01:56:08PM +0800, hacklu wrote:
>  I didn't understand the address mask.
> it's said that: BR[BA] is the base address,the OR[AM] is the  address mask,
> for instance, if my BR0[BA]=0111_0000_0000_0000_0, OR0[AM]=1111_1111_1111
> if I want to access the 0x70000000 or the 0x71000001.what address calculate will be taken?

Assuming that BR0 is set to valid, the right chip select machine is
selected, etc., my understanding of MPC885RM is:

* 0x70000000 & OR0[AM] = 0x70000000
  0x70000000 == BR0[BA]
  => CS0 active, 0x0000 on the address bus (haven't checked the actual
  bus width).

* 0x71000001 & OR0[AM] = 0x71000000
  0x71000000 != BR0[BA]
  => CS0 inactive, will check the following BR/ORs

With kind regards,
Baurzhan Ismagulov

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