Hi Yuchao,
You can put the .txt in the MSMC without worry to the coherency as the code is just reading and not writing regarding the other segments than you have the coherency issue with the DDR so you will have to handle it the same with the MSMC, the only thing is if you want the cache to work on the MSMC than you have to move the memory to a different address and than set the MAR's (check - http://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/639/t/171731.aspx),
Thanks,
HR