Hi, I know you folks like jtagging popular SoCs, and those broadcom families are pretty common in SOHO WiFi equipment. In my particular case I had Asus RT-N16 I wanted to tinker with.
After system reset those chips work in some undocumented "LV" mode so nothing really works. The IR length is 32 bits, some hints about it can be found at [1]. In particular, command 0xfffffffe allows to read IDCODE from a 32-bit DR. UrJTAG's "detect" prints nothing in this mode. To switch away from this nasty useless undocumented mode to standard EJTAG one needs to: 1. Shift 0x0143ff3a into IR, for this command DR is 32 bits too; end state apparently doesn't matter, e.g. run/idle is ok; 2. Shift 1 into DR, switch to run/idle; 3. Now the device is in standard EJTAG with IR length 5 (or 7 for some models), so one needs to reexamine the chain. I've tested this procedure on RT-N16 with OpenOCD and confirm I'm able to communicate with the target properly including halting, resuming, memory reading after performing this trick. Special DIScredit for this information goes to some dd-wrt people, specifically to "Lom" and "Tornado" who knew this for quite some time but decided to not share with anybody except some other proprietary "usbbdm" vendor. Shame on them! [1] https://github.com/RMerl/asuswrt-merlin/blob/f9c2e38eba437af5100faa186b874284602a2efb/release/src-rt-6.x.4708/include/hndjtagdefs.h -- Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software! mailto:fercer...@gmail.com ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349831&iu=/4140/ostg.clktrk _______________________________________________ UrJTAG-development mailing list UrJTAG-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/urjtag-development
