Saved FAQ from Freescale.com for information only:
Question. The iRAM area(0x1FFE_0000) is not accessible with JTAG (RV-ICE).
1. Please check if ARM core of the i.MX51 is in supervisor mode, when using JTAG. Say, sometimes it may be in thumb one, since internal bootloader uses the thumb mode.
2. "Strange" behavior may be detected, if some i.MX51 fuses are "unexpectedly" burned because of power up sequence violation. Let me remind, VDD_FUSE is recommended be floated and grounded.
3.After watchdog reset internal memory IRAM is not accessible. Note, internal and UART / USB bootloader start watchdog.
i.MX Applications Processors > i.MX51 Processors > i.MX512, i.MX513, i.MX514, i.MX515, i.MX516