Diff: com/com.cpp

Revision:

32:d2b973c8d196

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/com/com.cpp	Sun Jun 09 02:41:27 2013 +0000
@@ -0,0 +1,130 @@
+/****************************** com.cpp **********************************/
+/* Version: 1.0                                                          */
+/* Last Updated: June 1, 2013                                            */
+/*                                                                       */
+/* The com class implements reliable data transfer between two nodes     */
+/*using a checksum and a sequence number for guaranteed message delivery */
+/*over an xbee modem connected to the passed in tx and rx pins. Messages */
+/*are received and placed in the rxBuffer to be read when convenient.    */
+/*Messages are encoded by sending a byte with the value of the command   */
+/*then and int of the command.                                           */
+/*                                                                       */
+/* Commands:    0 -> Ack, does not get placed in rxQueue.                */
+/*              1 -> Throttle                                            */
+/*              2 -> Pitch                                               */
+/*              3 -> Roll                                                */
+/*              4 -> Yaw                                                 */
+/*************************************************************************/
+
+#include "mbed.h"
+#include "com.h"
+
+/*********************** com( PinName, PinName ) *************************/
+/*                                                                       */
+/*************************************************************************/
+
+com::com( PinName tx, PinName rx ) : xbee( tx, rx)
+{
+    bLength = 0;                            // How many bytes are in the buffer.
+    xbee.attach( this, &com::callback );    // Set callback as the interrupt handler. 
+    xbee.baud(BAUDRATE);                    // Setup the serial baud rate.
+    rxBuffer = new queue();                     // Point to the rxQueue.
+
+}
+
+/************************* bool isData()  ********************************/
+/*                                                                       */
+/*************************************************************************/
+
+bool com::isData()
+{
+    if( rxBuffer->isEmpty() )
+        return false;
+        
+    return true;
+}
+
+/************************ void write( char ) *****************************/
+/* Write a packet out the xbee com port.                                 */
+/*                                                                       */
+/* Data format byte[]                                                    */
+/*                byte[0] = command.                                     */
+/*                byte[1] = upper 8 bits of value.                       */
+/*                byte[2] = lower 8 bits of value.                       */
+/*                byte[3] = Checksum byte[0] + byte[2].                  */
+/*                byte[4] = Sequence Number.                             */
+/*                byte[5] = 255 End of message.                          */
+/*************************************************************************/
+
+void com::write( char command, int value  )
+{
+    xbee.putc( command );           // Command
+    xbee.putc( 0 );                 // First 8 bits in array. 
+    xbee.putc( (char)value );       // Second 8 bits in array.
+    xbee.putc( command + value );   // Checksum array[0] + array[1].
+    xbee.putc( 0 );                 // Sequence number.
+    xbee.putc( 255 );               // End of message.
+}
+
+/*************************** char read()  ********************************/
+/*                                                                       */
+/*************************************************************************/
+
+char * com::read()
+{
+    // Are there commands in the readBuffer queue?    
+    if( !rxBuffer->isEmpty())
+        return rxBuffer->pop();
+        
+    return NULL;
+}
+
+/************************ void callback() ********************************/
+/*                                                                       */
+/*************************************************************************/
+
+void com::callback()
+{   
+    while( xbee.readable() )
+    {
+        char data = xbee.getc(); 
+        if( bLength++ < 15 )
+            buffer[bLength] = data;      
+     
+        if( data == 255 )
+            packetBuilder();
+    }
+}
+
+/********************** void packetBuilder() *****************************/
+/* Creates a packet from the buffered data and places it in the rxBuffer */
+/*queue to be read whenever convenient.                                  */
+/*************************************************************************/
+
+void com::packetBuilder()
+{
+    char * commandData = new char[bLength];
+    commandData[4] = buffer[--bLength];     // Sequence Number.
+    commandData[3] = buffer[--bLength];     // CheckSum value.
+    commandData[2] = buffer[--bLength];     // Second 8 bits.
+    commandData[1] = buffer[--bLength];     // Fisrt 8 bits.
+    commandData[0] = buffer[--bLength];     // Command.
+            
+    if( commandData[0] + commandData[2] == commandData[3] ) // Validate checksum.
+    {
+        rxBuffer->add( commandData );   // Add to read buffer.
+        write( 0, (int)commandData[4]); // Ack the packet with sequence nuber.
+    } 
+    bLength = 0;    // Reset the buffer length.                                           
+}
+
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