If you get JTAG going, here is what you'll need uisng JTAG Commander (the segger tools, if using openocd, replace w1 with mwb and replace mem with mdb in the commands).
First "halt" the CPU while in the uboot prompt.
The first command should output 5 bytes identifying the chip manufacturer and a few parameters (the PBOOT checks this to see if it is natively supported).
Read ID:
w1 0xBAB10000 0x90
w1 0xBAB20000 0x0
mem 0xBAB00000 5
Next, PBOOT checks for the ONFI "magic" like this:
Read ONFI:
w1 0xBAB10000 0x90
w1 0xBAB20000 0x20
mem 0xBAB00000 4
This should return the letters "ONFI"
Finally, this next is the most likely place there could be an issue. It is the page PBOOT uses to configure itself. It tells it what kind of ECC is in use, as well as lots of other things that could break the boot process if it is wrong. For this reason, the manufacturer includes a checksum in this info, AND alternate copies of parameters later. PBOOT appears to ignore these things.
Read Parameter Page:
w1 0xBAB10000 0xEC
w1 0xBAB20000 0x0
mem 0xBAB00000 512
This will grab the complete parameters, with CRC and at least 1 redundant copy.
Make sure you don't resume the CPU after this. Just power cycle it, as you are putting the NAND into a mode UBOOT won't be aware of...