Is it high (IE. driven) or is it just floating? To quote the TI Technical Reference: “At reset, all the GPIO related pins are configured as input and output capabilities are disabled.” Unless the boot process or some program sets your pin up as an output, then it would just float in a high impedance state until your device tree stuff says otherwise. Does your peripheral device make that loud beep if it is powered but disconnected from P9.12?
If so, then you could change your circuit so it needs to be actively driven or sunk with a maximum of about 4 ma. (To stay within the current limits of a GPIO pin.) That could be as simple as adding a weak pulldown resistor. I would start with a 10K and watch with a scope during startup to see if it ever is driven high. You need to understand the current and voltage characteristics of anything you attach to a GPIO pin because you can burn up a GPIO (or even the whole chip) just by trying to drive an LED without a transistor or IC buffer. From: [email protected] Sent: Thursday, April 17, 2014 2:19 AM To: [email protected] Subject: [beagleboard] Change default state of GPIO pin I have a beeper which is controlled by GPIO P9.12. The problem is that the default state of this pin is high (I think this is the problem). So I have a long and annoying beep when the BBB boots. This stops when my programm is loaded, then everything works as it should. Is there a way to set the default state of this pin to low? Regards, Rob -- 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. -- 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.
