how to pass message from DSP side to ARM side on TI dsplink DM3730

I tried to pass message by a message buffer from DSP to ARM. I use dsplink sample message for test.
I added the following code to allocate a message buffer and translate GPP memory address to DSP one,

typedef struct _MSG_buf {
    MSGQ_MsgHeader header;
    Char8 *Msg_buf;
} MSG_buf;

    /*
     *  allocate the GPP's message buffer
     */
    status = POOL_alloc (POOL_makePoolId(processorId, SAMPLE_POOL_ID), (Void **) &MessageBuf, BUFSIZE) ;
    if (DSP_FAILED (status)) {
            MESSAGE_1Print ("POOL_alloc () failed. Status = [0x%x]\n",
                            status) ;
        }

    MESSAGE_1Print ("POOL_translateAddr () GPP address 0x%x\n", MessageBuf) ;
    status = POOL_translateAddr ( POOL_makePoolId(processorId, SAMPLE_POOL_ID),
                   &DspMessageBuf, AddrType_Dsp, (Void *) MessageBuf, AddrType_Usr);
    if (DSP_FAILED (status)) {
        MESSAGE_1Print ("POOL_translateAddr () failed. Status = [0x%x]\n",
                        status) ;
        POOL_free (POOL_makePoolId(processorId, SAMPLE_POOL_ID), (Void *) MessageBuf, BUFSIZE);
    } else
        MESSAGE_1Print ("POOL_translateAddr () successful DSP address 0x%x\n",
                        DspMessageBuf) ;

Then I write a message to MessageBuf and call
     msg->Msg_buf = DspMessageBuf;
     POOL_writeback(POOL_makePoolId(processorId, SAMPLE_POOL_ID), MessageBuf, BUFSIZE);
     status = MSGQ_put (SampleDspMsgq, (MSGQ_Msg) msg) ;

On the DSP side, I modified the message buffer as follows,
        status = MSGQ_get (info->localMsgq, (MSGQ_Msg *) &msg, SYS_FOREVER) ;
        MSGQ_setMsgId ((MSGQ_Msg) msg, info->sequenceNumber) ;
        MSGQ_setSrcQueue ((MSGQ_Msg) msg, info->localMsgq) ;
        memcpy(msg->Msg_buf, "hello", 6);

        /* Send the message back */
        status = MSGQ_put (info->locatedMsgq, (MSGQ_Msg) msg) ;

When I receive message on ARM side, the message is not changed. I don't know what are missing.
I also tried to allocate message buffer on DSP side and send message to ARM, but the buffer has nothing.

Thanks,
Kai