Writing Pin-muxing registers in an am3359.

Bob Stewart robjsstewart at ...196...
Thu Oct 24 18:20:16 CEST 2013

Understand what you mean now,  Christian. The registers I'm working with 
are read by the processor to determine what mode the gpio pins will run in 
(amongst other things),  so once set they should be readable. I'll do some 
testing with hardware to see if the mode changes are really taking effect. 
On this hardware there are eight modes per pin and,  depending on the mode, 
 the pin might simply be digital level  or it might output a PWM signal. So 
mode setting is important.

I pulled the "decaprox" branch from ksyslabs repository. That branch has a 
driver for am33xx gpio. I moved the changes for the am33xx gpio into my 
local copy of 13.08 along with test stubs. All that worked ok and I could 
get gpio pins to function as I wanted. The gpio driver does not however 
have functionality to set the pin modes and one is stuck with pins in the 
mode the boot rom sets.


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On October 24, 2013 11:30:46 AM Christian Helmuth 
<christian.helmuth at ...1...> wrote:
> Hej,
> On Thu, Oct 24, 2013 at 11:20:09AM -0400, Bob Stewart wrote:
> > Thanks for the reply Christian. If I'm writing to a local memory location 
> why would the change in value not show in the debugger, even if that 
> location is memory mapped to a hardware register?
> From my experience this heavily depends on the device behind the
> "memory location" as this is not RAM. The device may, for example,
> interpret bit 0 set on write as "clear register", which would gain you
> 0x0 on writing 0x1. Note, it was just a plain guess as I do not know
> your platform or device very well.
> BTW, which Ksyslabs repository and branch did you base your work on?
> Does it already include a GPIO driver for your BeagleBone?
> Regards
> --
> Christian Helmuth
> Genode Labs
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