I suspect the problem is not GPIO, something else seems to be muxed into the GPIO pins (maybe MMC2? But it is "disabled" in the DTS!). The GPIOs are accessible from U-Boot (via "gpio" commands), but they are NOT accessible from the Linux userspace.
cd /sys/class/gpio echo 137 > export cd gpio137 echo "low" > direction no effect! The /sys/kernel/debug/omap_mux/sdmmc2_dat7 is not present, so I cannot remux anything into the GPIO pins. Thanks! On Wednesday, October 23, 2013 3:58:27 PM UTC-4, porkupan wrote: > > Not touched via the DTS, but they are touched somehow. When I clear the > GPIO 137 (or 138 or 139, to which I have LEDs connected) in U-Boot, the > signal is correctly affected. Then I issue the boot command, and let the > Linux start up. As soon as the "Starting kernel ..." message comes out on > the serial port, all signals are back HIGH. So, whether there is a > peripheral reset of some kind that "resets" all these GPO signals, or they > are set in the C source, but they are definitely affected by kernel > startup. I am OK if they came up for a little bit, as long as we had a way > to set them LOW before the full system startup completes. > > Thanks! > > On Wednesday, October 23, 2013 10:09:15 AM UTC-4, RobertCNelson wrote: >> >> On Wed, Oct 23, 2013 at 8:58 AM, porkupan <vladimi...@gmail.com> wrote: >> > Thanks, I understand. Turns out what I needed could have been >> accomplished >> > without rebuilding U-Boot. I had to set the value of a GPIO line, and >> there >> > is a U-Boot script command for that. >> > >> > So, a re-built U-Boot wouldn't have produced any benefit. >> > >> > However, I need to figure out how to force this GPIO to stay LOW during >> > kernel startup. Apparently the kernel switches it HIGH (or affects >> some >> > sort of a reset that forces GPIO_137 high). So, the GPIO line is >> switched >> > down via "gpio clear 137" U-Boot command, but a couple of seconds later >> > comes back up, and stays up until the user software can be brought up >> to >> > switch it off. It seems that most interactions with the registers, >> > including setting GPIO levels, can be achieved via the DTS? I see some >> > examples for BBB, but haven't found anything for the xM. >> >> Well gpio_137 is not touched on mainline: >> >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/omap3-beagle-xm.dts >> >> >> Regards, >> >> -- >> Robert Nelson >> http://www.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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
