omapl138 starterware "ipc_buffer_io_arm5_omapl138_evmOMAPL138"

I run this example on my omapl138 bord,  arm and dsp can not communicate each other, I found this code in "notify.c" "while    (*ptr != IPC_BOOT_KEY)     ipc_quickWait();",  yes, it hung here, what IPC_BOOT_KEY meaning, can someone help me?