Nios II produces unreadable code after DMA on DDR SDRAM

Dear all,

After running DMA on DDR SDRAM, and verifying it successfully, Nios II produces unreadable code on the console, not ascII code characters any more.

Why this happens and how to slove it, anyone can help me, thanks!

The C - program is

ftp://ftp.altera.com/outgoing/download/kdb/ddr_test.c

The SOPC is similar to SOPC tutorials on External Memory Interface Handbook Volume 6.