Need GPIO pin voltage disabled at boot

[andrew otis]

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!

[evilwulfie]

you must use a tristate buffer to do this in hardware
it cannot be done in software

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[andrew otis]

Would you be able to offer expertise for compensation? I'm working on
a project and this requirement must be met, and it exceeds my
skillset.

Please, if you're interested and can help, email me!

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[William Pretty Security]

Sure I can help.
Reasonable rates, but I need more info.

Bill(dot)pretty(at)xplornet(dot)com

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