> Pins 3 through 46 on P8 are listed in the hardware > information as available for GPIO. Indeed, I can set any of them but > I notice that on pins 25 (gpio1_0), 21 (gpio1_30), and 20 (gpio1_31) > seem to be reserved by OpenBSD and great trouble is caused if I try to > set them with gpioctl(8) like I would for any other pin, e.g. like pin > 46 here:
> /usr/sbin/gpioctl gpio2 7 set out p8pin46; > Trial and error shows that setting pins 25, 21, and 20 causes trouble > right away. I was surprised by Theo's answer because I recall BeagleBone Black was open hardware, at least as a design. But I won't bet my hand on the board's ARM cpu. Anyway, I am not using it, I consider it for fun, but I checked it again and here it is: Excerpt from the hardware support: "BeagleBone Black ships with two virtual capes already on it, one for the on-board eMMC storage and one for the HDMI output. When configured for use these virtual capes consume actual resources. If the eMMC is not placed in reset, the MMC1* signals may not be used without potentially corrupting the contents of your on-board eMMC---and possibly damaging the physical circuit as well." The pins used by MMC1* are shown in the picture: 3, 4, 5, 6, 21, 22, 23, 24, 25.
