ZigBee applications - Part 6: Profiles

When the command is sent over-the-air, it looks like the following. This decode depicts command 0x01 which instructs the iPod to skip forward one song:

Frame 18 (Length = 28 bytes)
IEEE 802.15.4
        Frame Control: 0x8861
        Sequence Number: 205
        Destination PAN Identifier: 0x1aaa
        Destination Address: 0x0000
        Source Address: 0x796f
        Frame Check Sequence: Correct
ZigBee NWK
        Frame Control: 0x0048
        Destination Address: 0x0000
        Source Address: 0x796f
        Radius = 10
        Sequence Number = 219
ZigBee APS
        Frame Control: 0x00
        Destination Endpoint: 0x01
        Cluster Identifier: (0x0001)
        Profile Identifier: (0xc035)
        Source Endpoint: 0x01
        Counter: 0x4d
        Unknown APS Data: 01

Note the profile ID in the ZigBee APS frame (0xc035). This is a private profile assigned to San Juan Software by the ZigBee Alliance. In this profile, cluster 0x0001 means the "iPod" cluster. This cluster is defined to contain a single command byte in the payload, called "APS Data." The commands mirror the features available to the iPod controller.

• Play/Pause (cmd 0x00)
• Skip Forward (cmd 0x01)
• Skip Backward (cmd 0x02)
• Volume Up (cmd 0x03)
• Volume Down (cmd 0x04)

The data indication on the iPod Controller simply takes this command byte in and passes it along to the function SendiPodRemoteCommand(), which sends a corresponding command string over the serial port at 19,200 baud. The serial port is connected to the iPod via the 2-wire interface:

void BeeAppDataIndication(void)
{
    apsdeToAfMessage_t *pMsg;
    zbApsdeDataIndication_t *pIndication;
    while(MSG_Pending(&gAppDataIndicationQueue))
    {
        /* Get a message from a queue */
        pMsg = MSG_DeQueue(&gAppDataIndicationQueue);
        pIndication = & (pMsg- > msgData.dataIndication);

        /* is the cluster for the application */
        if(pIndication- > aClusterId == appDataCluster)
            SendiPodRemoteCommand(pIndication- > pAsdu[0]);

        /* Free memory allocated by data indication */
        MSG_Free(pMsg);
    }
}
void SendiPodRemoteCommand(iPodRemoteCommand_t cmd)
{
    uint8_t *pCmdPtr;

    switch(cmd) {
        case gPlayPause_c:
            pCmdPtr = PlayPause;
            break;
        case gSkipForward_c:
            pCmdPtr = SkipForward;
            break;
        case gSkipReverse_c:
            pCmdPtr = SkipReverse;
            break;
        case gVolumeDown_c:
            pCmdPtr = VolumeDown;
            break;
        case gVolumeUp_c:
            pCmdPtr = VolumeUp;
            break;
        default:
            pCmdPtr = ButtonRelease;
            break;
}

    /* send command-all commands are the same size */
    (void)UartX_Transmit(pCmdPtr, sizeof(PlayPause), NULL);
    while (!UartX_TxCompleteFlag);
    /* delay 100 microseconds before sending button release */
    DELAY_100US();
    /* Button release must always be sent after a command */
    UartX_Transmit(ButtonRelease, sizeof(ButtonRelease), NULL);
    while (!UartX_TxCompleteFlag);
}

On the sending end, the application simply creates a data request with the command-byte associated with the particular button:

void BeeAppHandleKeys(key_event_t keyEvent)
{
    switch(keyEvent) {

        /* play/pause */
        case gKBD_EventSW1_c:
            SendiPodRemoteCommandOTA(gPlayPause_c);
            break;

        /* skip one song forward */
        case gKBD_EventSW2_c:
            SendiPodRemoteCommandOTA(gSkipForward_c);
            break;

        /* skip one song reverse */
        case gKBD_EventLongSW2_c:
            SendiPodRemoteCommandOTA(gSkipReverse_c);
            break;

        /* volume down */
        case gKBD_EventSW3_c:
            SendiPodRemoteCommandOTA(gVolumeDown_c);
            break;

        /* volume up */
        case gKBD_EventSW4_c:
            SendiPodRemoteCommandOTA(gVolumeUp_c);
            break;
    }
}

void SendiPodRemoteCommandOTA(iPodRemoteCommand_t cmd)
{
    afAddrInfo_t addrInfo;
    uint8_t TransmitBuffer[1];

    /* copy iPod command to TransmitBuffer */
    TransmitBuffer[0] = cmd;

    /* set up address information */
    addrInfo.dstAddrMode = gZbAddrMode16Bit_c;
    Set2Bytes(addrInfo.dstAddr.aNwkAddr, 0x0000);
    addrInfo.dstEndPoint = appEndPoint;
    addrInfo.srcEndPoint = appEndPoint;
    Copy2Bytes(addrInfo.aClusterId, appDataCluster);
    addrInfo.txOptions = gApsTxOptionNone_c;
    addrInfo.radiusCounter = afDefaultRadius_c;

    /* send the data request */
    (void)AF_DataRequest( & addrInfo, sizeof(TransmitBuffer), TransmitBuffer, NULL);
}

Notice the data request is sent to node 0x0000. In a private profile the main application could be on node 0x0000, the ZigBee Coordinator, such as a gateway to the PC, or in this case, the iPod controller, making node discovery unnecessary.

The application uses appEndPoint for both the source and destination endpoints. Using a fixed endpoint makes private profiles a little easier, as no endpoint discovery is required. The cluster in this example is appDataCluster, the first cluster in the output cluster list.