Hi, I've been trying to get JTAG working on the Beaglebone classic. It works using the 2012 Angstrom distribution [1], but not on the newer Debian-based distributions. I eventually managed to track this down to the fact the kernel sets the lowest two bits of the CM_WKUP_DEBUGSS_CLKCTRL [2] register (located at 0x44e00414) to 0, which powers off the debug hardware on the AM335x.
I was able to get JTAG working again by writing a small kernel module that sets the register to the value it has when the board is reset (though I *think* it would be sufficient to just set the last two bits to 0b10): void __iomem *io = ioremap(0x44e00000, SZ_4K); iowrite32(0x52580002, io + 0x414); iounmap(io); My question is: is there any way to stop the Linux kernel from disabling JTAG automatically on startup? I know it happens sometime during the boot process (if I stop during U-Boot, JTAG works and the CM_WKUP_DEBUGSS_CLKCTRL has its default value), but I can't figure out what to change in the DTB or the kernel source to prevent this. Thanks, Brendan [1] I think this is because the kernel used there has this patch https://github.com/beagleboard/kernel/blob/3.8/patches/dma/0002-ARM-OMAP-Hack-AM33xx-clock-data-to-allow-JTAG-use.patch [2] As found in the AM335x TRM: https://www.ti.com/lit/ug/spruh73q/spruh73q.pdf -- 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]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/15acfe9b-39b2-4890-844f-00d85a4cf29ao%40googlegroups.com.
