how the bytes ordered in mpc8313

how the bytes ordered in mpc8313

[Yoni Levin]

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I have mpc83xx,

I saw that I need to use swab32 to any read\write operation from registers,

I don't understand why I need it?

Do I need it for all registers?

Why in the mpc8313 reference in registers description some bits look like
31,30,29,.,3,2,1,0

And some: 0,1,2,3.,30,31

Is it just mistake? Or some registers are different then other? 


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Re: how the bytes ordered in mpc8313

[Scott Wood]

Yoni Levin wrote:
> I have mpc83xx,
> 
> I saw that I need to use swab32 to any read\write operation from registers,

Only little endian registers (such as PCI).

> Why in the mpc8313 reference in registers description some bits look like
> 31,30,29,.,3,2,1,0
> 
> And some: 0,1,2,3.,30,31

Most PowerPC documentation numbers bits in the same endianness as the 
bytes in the register.

> Is it just mistake? Or some registers are different then other? 

I consider big-endian bit numbering to be a mistake, but good luck 
getting them to fix it. :-)

-Scott

Re: how the bytes ordered in mpc8313

[Scott Wood]

Yoni Levin wrote:
> I have mpc83xx,
> 
> I saw that I need to use swab32 to any read\write operation from registers,

BTW, you should be using in/out_le32() (or for PCI MMIO, readl/writel) 
rather than swab32().  This will be more efficient since it can use the 
lwbrx/stwbrx instructions, and it will keep working even if the code is 
run little-endian.

-Scott