On Thu, Aug 6, 2015 at 9:28 AM, Axel Barkow <[email protected]> wrote: > Hi, > > I need to set a GPIO output high as early as possible during the startup and > keep it active until the system shuts down. What I did so far: > > - Use GPIO 0.7 for testing > - Set GPIO0.7 high in python script automatically after startup -> GPIO > becomes high approx. 24s after power-on > - Modify device tree to set GPIO0.7 high -> GPIO becomes high approx. 9s > after startup > - Set GPIO0.7 high in u-boot scipt (/boot/boot.scr) -> GPIO becomes high > after approx. 3.5s, but becomes low again after approx. 6s > > My problem now is that the GPIO becomes low for approx. 3s after it was set > by u-boot and before the device tree. I guess I need to understand the > kernel boot process a little bit better. Any suggestion, where to start or > any hint where to look at?
use the 'gpio-hog' option so the kernel doesn't re-set the gpio upon startup... See the example to keep the eMMC in reset: https://github.com/beagleboard/linux/blob/4.1/arch/arm/boot/dts/am335x-boneblack-overlay.dts#L28-L36 Regards, -- Robert Nelson https://rcn-ee.com/ -- 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.
