How to set DBGEN signal so that I can enter debug monitor mode?

I am in the process of writing a debug monitor for my BeagleBoard and when I dump the AUTHSTATUS register at address 0x54011fb8 I get back a value of 0xAE which from what I read in section 12.5.10 of the Cortex-A8 TRM would appear to indicate that NIDEN is set to enable non-invasive debugging but DBGEN isn’t set.

At I see that the OpenOCD crew is setting bit 13 at address 0x5401d030 to enable the DBGEN signal. I have attempted to set bit 13 at address 0x5401d030 from software running on the OMAP3530 but my write just appears to be ignored. Is it only possible to enable DBGEN on the OMAP3530 over the JTAG interface?

Thanks for the help,