Here a picture to show, what I measured. KL 15 is the external start signal, BBB 3.3V is the 3.3V line of the BBB and POWER HOLD is GPIO0.7. At T1 the power is switched on and at T2 I think that the GPIO is set by the device tree configuration.
Regards Axel <https://lh3.googleusercontent.com/-ej2Mnld8X4s/VcN2R3Od_PI/AAAAAAAAACM/u-IKwgOgI6w/s1600/screenshot.png> Am Donnerstag, 6. August 2015 16:53:44 UTC+2 schrieb Axel Barkow: > > Hi Robert, > > thanks, that improved the situation, but the GPIO is still going low for > approx. 500ms. Any further suggestion? > > Regards > > Axel > > Am Donnerstag, 6. August 2015 16:32:38 UTC+2 schrieb RobertCNelson: >> >> 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.
