Just a s what I said above, after a long testing process, we made the conclusion that at least one of the DSPs on the JTAG chain was broken (maybe both of them). so we had nothing to do but to replace both of the DSPs, and that really works.
We think the DSP was destroied by improper operation, that is, pulling out and pluging in the emulator while the power is still on. This is a very good lesson to us.
hope this can help.