JTAG Hardware HowTos
All memory accesses (including md/mw commands and disassembly) execute through the debug AHB on the L3 interconnect; resources on the L2 interconnect currently can not be accessed. This includes ROM, local PRCM, and anything in the Cortex-A9 "private memory region" (snoop-control unit, global interrupt controller, timers and watchdogs).
debugging A9 cores simultaneously is currrently not supported
The debugger may not be able to access the A9 processor cores due to an issue with omap4430 clocking. If your debugger can identify JTAG devices, e.g.:
Info : 375 316 core.c:948 jtag_examine_chain_display(): JTAG tap: omap4430.jrc tap/device found: 0x3b95c02f (mfg: 0x017, part: 0xb95c, ver: 0x3)
but no Cortex-A9 target appears, you are probably running into this issue. Verify by connecting the debugger with no SD card inserted: if it now works, you're hitting this issue.
The current x-loader mainline includes a workaround.