GPIO endianness on MPC8349

GPIO endianness on MPC8349

[Ben Warren]

Hello,

I'm a noobie to this CPU, and am utterly confused with how the bits are
ordered on the GPIO ports.  I imagine it's the same as all Freescale
PPCs, but who knows.  Anyway...

Using an MPC8349MDS eval board, I have one LED to play with.  From the
schematic, it's connected to GPIO1[1].  From other processors that I've
worked with, I would have expected to toggle it with either 0x40000000
(IBM 405) or 0x00000002 (68360).  Nope.  To make this bit move, I mess
with bit 0x00000040 in the appropriate DAT register.  This leads me to
believe that either the bit ordering is something
like ...89abcdef01234567 (sorry for the confusing notation, but
hopefully it makes sense) or the schematic has a typo.  Since I'm trying
to write a generic GPIO handler, I'd like to have a little confidence in
my extrapolation from a single point.

Can anybody shed some light on this?

thanks,
Ben

Re: GPIO endianness on MPC8349

[Kumar Gala]

On Apr 10, 2006, at 2:48 PM, Ben Warren wrote:

> Hello,
>
> I'm a noobie to this CPU, and am utterly confused with how the bits  
> are
> ordered on the GPIO ports.  I imagine it's the same as all Freescale
> PPCs, but who knows.  Anyway...
>
> Using an MPC8349MDS eval board, I have one LED to play with.  From the
> schematic, it's connected to GPIO1[1].  From other processors that  
> I've
> worked with, I would have expected to toggle it with either 0x40000000
> (IBM 405) or 0x00000002 (68360).  Nope.  To make this bit move, I mess
> with bit 0x00000040 in the appropriate DAT register.  This leads me to
> believe that either the bit ordering is something
> like ...89abcdef01234567 (sorry for the confusing notation, but
> hopefully it makes sense) or the schematic has a typo.  Since I'm  
> trying
> to write a generic GPIO handler, I'd like to have a little  
> confidence in
> my extrapolation from a single point.
>
> Can anybody shed some light on this?

This is because the Freescale docs are misleading.  If you look at  
the schematic you will see the LED is wired to GPIO1[5] which makes  
sense for the 0x40 value you have to use.

- kumar

Re: GPIO endianness on MPC8349

[Ben Warren]

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Sorry for wasting bandwidth (again).  Turns out my schematic is for an
earlier spin of the board.

regards,
Ben

On Mon, 2006-04-10 at 15:06 -0500, Kumar Gala wrote:

> On Apr 10, 2006, at 2:48 PM, Ben Warren wrote:
> 
> > Hello,
> >
> > I'm a noobie to this CPU, and am utterly confused with how the bits  
> > are
> > ordered on the GPIO ports.  I imagine it's the same as all Freescale
> > PPCs, but who knows.  Anyway...
> >
> > Using an MPC8349MDS eval board, I have one LED to play with.  From the
> > schematic, it's connected to GPIO1[1].  From other processors that  
> > I've
> > worked with, I would have expected to toggle it with either 0x40000000
> > (IBM 405) or 0x00000002 (68360).  Nope.  To make this bit move, I mess
> > with bit 0x00000040 in the appropriate DAT register.  This leads me to
> > believe that either the bit ordering is something
> > like ...89abcdef01234567 (sorry for the confusing notation, but
> > hopefully it makes sense) or the schematic has a typo.  Since I'm  
> > trying
> > to write a generic GPIO handler, I'd like to have a little  
> > confidence in
> > my extrapolation from a single point.
> >
> > Can anybody shed some light on this?
> 
> This is because the Freescale docs are misleading.  If you look at  
> the schematic you will see the LED is wired to GPIO1[5] which makes  
> sense for the 0x40 value you have to use.
> 
> - kumar

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