On 04/15/2013 03:51 PM, Mauro Carvalho Chehab wrote:
Em Sun, 14 Apr 2013 22:35:05 +0200
Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> escreveu:
I checked the em25xx datasheet (excerpt) and it talks about separate
registers for GPIO configuration (unfortunately without explaining their
function in detail).
Interesting. There are several old designs (bttv, saa7134,...) that uses
a separate register for defining the input and the output pins.
That's pretty usual way, likely most common, having separate GPIO
configuration and GPIO value registers. If you has a port of GPIO values
in one register, and you has configured those as 0-3 INPUT and 4-7
OUTPUT, then writing to that register does not make any changes to bits
that are mapped as IN (are just discarded as don't care).
In case a bit I/O (which is not not supported by Kernel) writing to
input register could enable internal pull-up or pull-down resistor :)
IIRC Atmel micro-controllers has such option.
regards
Antti
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