It uses https://github.com/dustcloud/sm_clib/blob/REL-1.0.1.4 to illustrate the concepts described.

This recipe is targeted at enthusiasts who want to understand the internals of the C Library. You do not need this level of understanding if you just want to use it.

1 Issuing the request
2 Handling the response
- 2.1 dn_hdlc_init() (dn_hdlc.c)

The C Library allows your micro-controller to issue commands to your SmartMesh device.

To illustrate, imagine you want to know the network id your SmartMesh IP manager is using, and therefore issue the getNetworkConfig command.

Issuing the request

If you use the C Library, all you need to do is call dn_ipmg_getNetworkConfig(), and pass a pointer to hold the reply.

dn_err_t dn_ipmg_getNetworkConfig(dn_ipmg_getNetworkConfig_rpt* reply);

The body of the dn_ipmg_getNetworkConfig() is:

/**
The getNetworkConfig command returns general network configuration parameters,
including the Network ID, bandwidth parameters and number of motes.
*/
dn_err_t dn_ipmg_getNetworkConfig(dn_ipmg_getNetworkConfig_rpt* reply) {
   uint8_t    extraFlags;
   dn_err_t   rc;
    
   // lock the module
   dn_lock();
    
   // verify no ongoing transmissions
   if (dn_ipmg_vars.busyTx) {
      // unlock the module
      dn_unlock();
       
      // return
      return DN_ERR_BUSY;
   }
    
   // store callback information
   dn_ipmg_vars.cmdId          = CMDID_GETNETWORKCONFIG;
   dn_ipmg_vars.replyContents  = (uint8_t*)reply;
    
   // extraFlags
   extraFlags = 0x00;
    
   // build outputBuf
    
   // send outputBuf
   rc = dn_serial_mg_sendRequest(
      CMDID_GETNETWORKCONFIG,                                   // cmdId
      extraFlags,                                               // extraFlags
      dn_ipmg_vars.outputBuf,                                   // payload
      DN_GETNETWORKCONFIG_REQ_LEN,                              // length
      dn_ipmg_getNetworkConfig_reply                            // replyCb
   );
    
   if (rc==DN_ERR_NONE) {
      // I'm not busy transmitting
      dn_ipmg_vars.busyTx         = TRUE;
   }
    
   // unlock the module
   dn_unlock();
    
   return rc;
    
}

After a number of checks, dn_ipmg_getNetworkConfig() calls dn_serial_mg_sendRequest(), which calls dn_serial_sendRequestNoCheck():

dn_err_t dn_serial_sendRequestNoCheck(uint8_t cmdId, bool isAck, bool shouldBeAcked, uint8_t* payload, uint8_t length, dn_serial_reply_cbt replyCb) {
   uint8_t i;
   uint8_t control;
    
   // register reply callback
   dn_serial_mg_vars.replyCmdId      = cmdId;
   dn_serial_mg_vars.replyCb         = replyCb;
    
   // create the control byte
   control         = 0;
   if (isAck==1) {
      control     |= DN_SERIAL_FLAG_ACK;
   } else {
      control     |= DN_SERIAL_FLAG_DATA;
   }
   if (shouldBeAcked==1) {
      control     |= DN_SERIAL_FLAG_ACKNOWLEDGED;
   } else {
      control     |= DN_SERIAL_FLAG_UNACKNOWLEDGED;
   }
    
   // send the frame over serial
   dn_hdlc_outputOpen();
   dn_hdlc_outputWrite(control);                      // Control
   dn_hdlc_outputWrite(cmdId);                        // Packet Type
   dn_hdlc_outputWrite(dn_serial_mg_vars.txPacketId);    // Seq. Number
   dn_hdlc_outputWrite(length);                       // Payload Length
   for (i=0; i<length; i++) {                         // Payload
      dn_hdlc_outputWrite(payload[i]);
   }
   dn_hdlc_outputClose();
    
   // increment the txPacketId
   dn_serial_mg_vars.txPacketId++;
    
   return DN_ERR_NONE;
}

The HDLC module of the C Library implements "on-the-fly" HDLC framing, which is particularly interesting for constrained devices. Rather than having a buffer which holds the packet to be sent and calculating the CRC in one go, the HDLC module escapes characters and calculates the CRC as it is receiving bytes from the caller, and sends those onto the serial port.

To output a HDLC frame, use:

dn_hdlc_outputOpen();         // prepares the HDLC module for outputting a new frame
dn_hdlc_outputWrite(byte1);   // call for each character
...
dn_hdlc_outputWrite(byten);
dn_hdlc_outputClose();        // wraps up the calculation of the CRC

The function your code initially called, dn_ipmg_getNetworkConfig(), now returns.

This function returns as soon as the request has left the serial port. It does not mean you have received a response from the device.

Internally, the C Library is now waiting for a reply to that function, and keeps the state in the table below:

variable	value	meaning

variable	value	meaning
`dn_ipmg_vars.busyTx`	`TRUE`	The C Library is busy transmitting. Any calls to issue new commands are rejected as long as: the response for that command isn't received, or the application calls `dn_ipmg_cancelTx()`, typically when timing out
`dn_ipmg_vars.cmdId`	integer	The identifier of the request just transmitted. Used to match the response.
`dn_ipmg_vars.replyContents`	pointer	A pointer to where to write the response.
variable	value	meaning
`dn_serial_mg_vars.replyCmdId`	integer	The identifier of the reply to wait for (same value as `dn_ipmg_varscmdId`).
`dn_serial_mg_vars.replyCb`	pointer	A function pointer to the function to call when a reply is received. For example, `dn_ipmg_getNetworkConfig_reply()`.

Handling the response

Each time a serial byte is received from the device, the dn_hdlc_rxByte() function is called.

/**
\brief Function which getted called each time a byte is received over UART.
\param[in] rxbyte The received byte.
*/
void dn_hdlc_rxByte(uint8_t rxbyte) {
    
   // lock the module
   dn_lock();
    
   if        (
         dn_hdlc_vars.busyReceiving==FALSE  &&
         dn_hdlc_vars.lastRxByte==DN_HDLC_FLAG &&
         rxbyte!=DN_HDLC_FLAG
      ) {
      // start of frame
       
      // I'm now receiving
      dn_hdlc_vars.busyReceiving       = TRUE;
       
      // create the HDLC frame
      dn_hdlc_inputOpen();
       
      // add the byte just received
      dn_hdlc_inputWrite(rxbyte);
   } else if (
         dn_hdlc_vars.busyReceiving==TRUE   &&
         rxbyte!=DN_HDLC_FLAG
      ){
      // middle of frame
       
      // add the byte just received
      dn_hdlc_inputWrite(rxbyte);
       
      if (dn_hdlc_vars.inputBufFill+1>DN_HDLC_INPUT_BUFFER_SIZE) {
         // input buffer overflow
         dn_hdlc_vars.inputBufFill       = 0;
         dn_hdlc_vars.busyReceiving      = FALSE;
      }
   } else if (
         dn_hdlc_vars.busyReceiving==TRUE   &&
         rxbyte==DN_HDLC_FLAG
      ) {
      // end of frame
       
      // finalize the HDLC frame
      dn_hdlc_inputClose();
       
      if (dn_hdlc_vars.inputBufFill==0) {
         // invalid HDLC frame
      } else {
         // hand over frame to upper layer
         dn_hdlc_vars.rxFrame_cb(&dn_hdlc_vars.inputBuf[0],dn_hdlc_vars.inputBufFill);
          
         // clear inputBuffer
         dn_hdlc_vars.inputBufFill=0;
      }
       
      dn_hdlc_vars.busyReceiving = FALSE;
   }
    
   dn_hdlc_vars.lastRxByte = rxbyte;
    
   // unlock the module
   dn_unlock();
}

Similar to the transmission case, the HDLC module implements "on-the-fly" HDLC de-framing using the following functions:

dn_hdlc_inputOpen()
dn_hdlc_inputWrite()
dn_hdlc_inputClose()

When done receiving a correctly-formatting HDLC frame, the dn_hdlc_vars.inputBuf buffer contains the un-framed response. It is handed to the "upper-layer" through the callback function dn_hdlc_vars.rxFrame_cb().

Note that that this callback function was installed when the HDLC module was initialized:

dn_hdlc_init() (dn_hdlc.c)

/**
\brief Setting up the instance.
*/
void dn_hdlc_init(dn_hdlc_rxFrame_cbt rxFrame_cb) {
   // reset local variables
   memset(&dn_hdlc_vars,   0, sizeof(dn_hdlc_vars));
    
   // store params
   dn_hdlc_vars.rxFrame_cb = rxFrame_cb;
    
   // initialize UART
   dn_uart_init(dn_hdlc_rxByte);
}

Which itself is installed by the dn_serial_mg module, and points to dn_serial_mg_rxHdlcFrame().

When the received frame is handed to dn_serial_mg_rxHdlcFrame(), it has the following format:

1B	1B	1B	1B	variable
`control`	`cmdId`	`seqNum`	`length`	payload

The flags in the control byte allow the dn_serial_mg module to distinguish a response from a notification. This allows notifications to be handled even when the module is waiting for a response.

The payload is handed to the dn_serial_mg_dispatch_response() function:

void dn_serial_mg_dispatch_response(uint8_t cmdId, uint8_t* payload, uint8_t length) {
   uint8_t rc;
    
   rc = payload[0];
   if (cmdId==dn_serial_mg_vars.replyCmdId && dn_serial_mg_vars.replyCb!=NULL) {
       
      // call the callback
      (dn_serial_mg_vars.replyCb)(cmdId,rc,&payload[1],length-1);
       
      // reset
      dn_serial_mg_vars.replyCmdId   = 0x00;
      dn_serial_mg_vars.replyCb      = NULL;
   }
}

At this point, the payload contains:

1B	variable
`rc`	payload

Which only continues handling this packet if this response corresponds to the request sent earlier. The dn_serial_mg_dispatch_response() function strips the return code, and hands the payload to the reply handler, in our case dn_ipmg_getNetworkConfig_reply().

Finally, dn_ipmg_getNetworkConfig_reply() verifies the length of the payload, and populates the fields of the reply buffer dn_ipmg_vars.replyContents.

void dn_ipmg_getNetworkConfig_reply(uint8_t cmdId, uint8_t rc, uint8_t* payload, uint8_t len) {
   dn_ipmg_getNetworkConfig_rpt* reply;
    
   // verify I'm expecting this answer
   if (dn_ipmg_vars.busyTx==FALSE || dn_ipmg_vars.cmdId!=cmdId) {
      return;
   }
    
   // verify length
   if (rc==DN_SERIAL_RC_OK && len<DN_GETNETWORKCONFIG_REPLY_LEN) {
      return;
   }
    
   // cast the replyContent
   reply = (dn_ipmg_getNetworkConfig_rpt*)dn_ipmg_vars.replyContents;
    
   // store RC
   reply->RC = rc;
    
   // parse returned value (iff RC==0)
   if (rc==DN_SERIAL_RC_OK) {
       
      dn_read_uint16_t(&reply->networkId,&payload[DN_GETNETWORKCONFIG_REPLY_OFFS_NETWORKID]);
      reply->apTxPower = (int8_t)payload[DN_GETNETWORKCONFIG_REPLY_OFFS_APTXPOWER];
      reply->frameProfile = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_FRAMEPROFILE];
      dn_read_uint16_t(&reply->maxMotes,&payload[DN_GETNETWORKCONFIG_REPLY_OFFS_MAXMOTES]);
      dn_read_uint16_t(&reply->baseBandwidth,&payload[DN_GETNETWORKCONFIG_REPLY_OFFS_BASEBANDWIDTH]);
      reply->downFrameMultVal = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_DOWNFRAMEMULTVAL];
      reply->numParents = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_NUMPARENTS];
      reply->ccaMode = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_CCAMODE];
      dn_read_uint16_t(&reply->channelList,&payload[DN_GETNETWORKCONFIG_REPLY_OFFS_CHANNELLIST]);
      reply->autoStartNetwork = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_AUTOSTARTNETWORK];
      reply->locMode = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_LOCMODE];
      reply->bbMode = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_BBMODE];
      reply->bbSize = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_BBSIZE];
      reply->isRadioTest = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_ISRADIOTEST];
      dn_read_uint16_t(&reply->bwMult,&payload[DN_GETNETWORKCONFIG_REPLY_OFFS_BWMULT]);
      reply->oneChannel = payload[DN_GETNETWORKCONFIG_REPLY_OFFS_ONECHANNEL];
   }
    
   // call the callback
   dn_ipmg_vars.replyCb(cmdId);
    
   // I'm not busy transmitting anymore
   dn_ipmg_vars.busyTx=FALSE;
}

At this point, the dn_ipmg module indicates a response was received by calling the dn_ipmg_vars.replyCb() callback function. The application can now read the response in the dn_ipmg_getNetworkConfig_rpt buffer it passed initially when calling dn_ipmg_getNetworkConfig().

How the C library issues commands

Issuing the request

Handling the response

dn_hdlc_init() (dn_hdlc.c)