you must use a tristate buffer to do this in hardware it cannot be done in software
On 6/27/2015 8:14 AM, andrew otis wrote: > I'm a n00b, but I have a requirement to make a few of my GPIO pins not > output any voltage during boot. > > I've got a new beaglebone black. > > I can disable them through the /sys/class/gpio/export just fine but > doing so in a bash script on boot leaves current through the pin for > about 4-5 seconds before it runs my script. > > So next, I looked into modifying the boot loader. I tried commenting > out the bottom section of beagle.c: > > > /* Set GPIO states before they are made outputs > writel(GPIO23 | GPIO10 | GPIO8 | GPIO2 | GPIO1, > &gpio6_base->setdataout); > writel(GPIO31 | GPIO29 | GPIO28 | GPIO22 | GPIO21 | > GPIO15 | GPIO14 | GPIO13 | GPIO12, > &gpio5_base->setdataout); */ > > /* Configure GPIOs to output > writel(~(GPIO23 | GPIO10 | GPIO8 | GPIO2 | GPIO1), > &gpio6_base->oe); > writel(~(GPIO31 | GPIO29 | GPIO28 | GPIO22 | GPIO21 | > GPIO15 | GPIO14 | GPIO13 | GPIO12), &gpio5_base->oe); */ > > dieid_num_r(); > > and recompiled and tested and there is still voltage coming from pin > 11 during boot. > > Would someone that has experience doing this at least point me in the > right direction? It would be so much appreciated! > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google > Groups "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send > an email to [email protected] > <mailto:[email protected]>. > For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
