They can be written only in privileged mode; if you're using Linux, this means that you have to be in kernel space to write. Refer https://github.com/chunsj/nxctrl/blob/master/nxpmx/nxpmx.c which my approach or you can use PRU code.
-----Original Message----- From: "serge.ns...@gmail.com" <serge.ns...@gmail.com> Sent: 7/4/2014 12:35 PM To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Subject: [beagleboard] Re: set up PADCONF for am33xx from userspace Control module registers are write protected. -- 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/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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.