how to understand powerpc's BRx ORx

how to understand powerpc's BRx ORx

[hacklu]

 I didn't understand the address mask.
it's said that: BR[BA] is the base address,the OR[AM] is the  address mask,
"Provides masking for corresponding BRx bits. By masking address 
bits independently, SDRAM devices of different size address ranges can be used. Clearing 
bits masks the corresponding address bit. Setting bits causes the corresponding address 
bit to be compared with the address pins. Address mask bits can be set or cleared in any 
order, allowing a resource to reside in more than one area of the address map. SDAM can 
be read or written at any time."

how to understand it?
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?

thanks all
 				
--------------
hacklu
2010-09-10

Re: how to understand powerpc's BRx ORx

[Kumar Gala]

On Sep 10, 2010, at 12:56 AM, 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,
> "Provides masking for corresponding BRx bits. By masking address=20
> bits independently, SDRAM devices of different size address ranges can =
be used. Clearing=20
> bits masks the corresponding address bit. Setting bits causes the =
corresponding address=20
> bit to be compared with the address pins. Address mask bits can be set =
or cleared in any=20
> order, allowing a resource to reside in more than one area of the =
address map. SDAM can=20
> be read or written at any time."
>=20
> how to understand it?
> for instance, if my BR0[BA]=3D0111_0000_0000_0000_0, =
OR0[AM]=3D1111_1111_1111
> if I want to access the 0x70000000 or the 0x71000001.what address =
calculate will be taken?

Can you let us know which chip you are looking at using?  There is a bit =
of variation so its useful to know.

- k=

Re: how to understand powerpc's BRx ORx

[Baurzhan Ismagulov]

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
http://www.kz-easy.com/