On Thu, 18 Jun 2020 13:10:59 -0400, in gmane.comp.hardware.beagleboard.user
Dennis Lee Bieber <[email protected]>
wrote:
>
> Or managing to read the config-pin /script/ source and figuring out how
>to invoke the equivalent directly <G>
... which appears to be sysfs writes...
Note -- there appears to be an error at line 1446 of the script
version... It is setting PULL-DOWN, but is in a block of code that is
supposed to be setting PULL-UP. Looks like a cut&paste of lines 1414-1430
(setting pull-down), to 1432-1448, in which three of the four _pd where
changed to _pu.
# GPIO with pull-up enabled
[iI][nN]+|[iI][nN][pP][uU][tT]+|[iI][nN][-_][pP][uU]|[iI][nN][pP][uU][tT][-_][pP][uU])
MODE=gpio_pu;
DIR=in
;;
[oO][uU][tT]+|[oO][uU][tT][pP][uU][tT]+|[oO][uU][tT][-_][pP][uU]|[oO][uU][tT][pP][uU][tT][-_][pP][uU])
MODE=gpio_pu;
DIR=out
;;
[lL][oO]+|[lL][oO][wW]+|0+|[lL][oO][-_][pP][uU]|[lL][oO][wW][-_][pP][uU]|0[-_][pP][uU])
MODE=gpio_pu;
DIR=low
;;
[hH][iI]+|[hH][iI][gG][hH]+|1+|[hH][iI][-_][pP][uU]|[hH][iI][gG][hH][-_][pP][uU]|1[-_][pP][uU])
MODE=gpio_pd; <<<<< line 1446, compare to
previous three
DIR=high
;;
Direction is written via (trimmed)(line 1470)
if [ -n "$DIR" ] ; then
eval GPIO="\$${PIN}_GPIO"
FILE="$GPIODIR/gpio$GPIO/direction"
if [ -e $FILE ] ; then
if [ -w $FILE ] ; then
echo $DIR > $FILE || (echo_err "Cannot
write gpio
direction file: $FILE" && exit 1)
and mode is written (line 1484 -- note that I think I only showed the post
3.8 kernel)
if [ ! "x${SLOTS_LOCATION}" = "xold38kernel" ] ; then
# Expand filename using shell globbing
for FILE in $OCPDIR${PIN}_pinmux/state ; do
echo_dbg "echo $MODE > $FILE"
if [ -w $FILE ] ; then
echo $MODE > $FILE || (echo_err "Cannot
write pinmux
file: $FILE" && exit 1)
So... from C/C++ determining the sysfs file names for the pins, and
writing the direction and mode strings to the proper files would be the
direct way. I believe most newer images have put the "debian" user into a
group with GPIO write access (I snipped the "else" branch which invokes the
write using sudo -- I'm presuming [-w ...] is a test for "is file
writable")
--
Dennis L Bieber
--
For more options, visit http://beagleboard.org/discuss
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