Re: hal/arm/at91/../var_io.h: HAL_ARM_AT91_GPIO_GET

[JÃrgen Lambrecht <J dot Lambrecht at televic dot com>]

Nick Garnett wrote:
> JÃrgen Lambrecht <J.Lambrecht@televic.com> writes:
>
>   
> > Hello,
> >
> > The current implementation of HAL_ARM_AT91_GPIO_GET in
> > hal/arm/at91/../var_io.h uses the AT91_PIO_PDSR register.
> > But, "Reading the I/O line levels requires the clock of the PIO
> > Controller to be enabled". So if you forget to enable the related PIO
> > clock, this HAL_ARM_AT91_GPIO_GET always fails!
> > Therefore, I propose to use the AT91_PIO_ODSR register.
> > Anyhow, the added value of PDSR over ODSR is small I think:
> > -with ODSR you read the value you want this pin to be
> > -with PDSR you read the actual (physical) value of this pin
> > They are only different if there is a hardware problem..
> >     
>
> Without reading the documentaion: the ODSR give you the contents of
> the output latch, while PDSR reads the line value.  ODSR and PDSR
> should agree for output pins, but for inputs the ODSR may differ from
> the line level, since it is no longer connected to the pin and pin is
> being driven to its current level by some external device.
>   
Indeed. So in general, my proposition is wrong.
I then propose to make an "OUT" version of that macro.
> Also, surely if you are using a GPIO port you should be enabling its
> clock. I would consider not doing that a programming error.
>   
No, only for an input you must enable the PIO clock: the PIO clock is 
then used to sample the input signal.
For an output, you just write the output register from your application, 
using the application clock.

Kind regards,
JÃrgen
> --
> Nick Garnett                                      eCos Kernel Architect
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