Diff: main.cpp

Revision:

8:2b61de165543

Parent:

7:aeeb441a68b8

Child:

9:77ae456366f7

--- a/main.cpp	Thu Apr 02 14:38:05 2015 +0000
+++ b/main.cpp	Mon Apr 13 17:11:10 2015 +0000
@@ -1,37 +1,107 @@
-//project to include preamble, addressing, control, error control.
-//currently fixed size data field but doesn't have to be. (post amble if not fixed size)
+//project to include preamble, addressing, post amble, crc error control.
 
 #include "mbed.h"
 #include "stdio.h"
 
-#define MAX 100 //set the size of the character data storage array
+#define MAX 100 //set the max size of the character data storage array
+#define BYTE 128
+#define NIBBLE 8 //used to set binary position of msb
 #define PREAMBLE 0x7E //preamble of 01111110
-#define ADDRESS 0x02 //address of 00000010
+#define POSTAMBLE 0x81 //postamble of 10000001
+//addressing 1st 4 bits indicate the network, 2nd 4 bits indicate the station id
+#define ADDRESS 0x12 //address of 00010010 network = 1, station id = 2
+#define BROADCAST 0x00 //broadcast address of 00000000
+#define MULTICAST 0x10 //broadcast to only network 1, all stations
+#define CRC 0x13 //crc of 10011 or x^4+x+1 or crc-5
 
 DigitalOut myled(LED1); // red led on board
-DigitalOut clock_pin(D8), serial_out(D7); //send clock pulse and tx
+DigitalOut clock_pin(D8), serial_out(D7); //send clock pulse and data
 Timer t; //timer for controlling the clock and data skew
 int msecs, sksecs; //clock time needed for data transfer and skew time
-int skew_flag; //skew flag for while loop
-unsigned char pre = PREAMBLE, add = ADDRESS;
-unsigned char data[100] = "Hi!"; //data output
-int done = 0,sent = 0 ,i = 0, j = 0; //increment variables
-void send_byte(int byte);
+unsigned char pre = PREAMBLE, add = BROADCAST, post = POSTAMBLE, crc_value = 0; //protocol overhead
+unsigned char data[MAX] = "Hi Kyle!\n"; //data output
+int crc_temp = 0; //temporary crc variable
+unsigned char sent = 0, i = 0, j = 0, skew_flag; //increment variables and flags
+
+//function prototypes
+//send a byte of data, for preamble, postamble, address, and data with BYTE, crc with NIBBLE
+void send_byte(unsigned char byte, int position);
+
+//calculate the crc value to send.
+unsigned char calculate_crc(int crc_bytes);
+
+
+int main()
+{
+
+    //turn on red led to show programming has worked
+    myled = 0;
+    //initialize output pins
+    clock_pin = 0;
+    serial_out = 0;
+    //skew flag
+    skew_flag = 1;
+    //set timers
+    msecs = 100;
+    sksecs = 80;
 
-void send_byte(int byte)
+    //output preamble
+    send_byte(pre, BYTE);
+    //output address
+    send_byte(add, BYTE);
+    //output data
+    while(!sent)
+    {
+        //finished sending data when string termination found
+        if(data[i] == '\n')
+        {
+            sent = 1;
+        }
+        //string still has data send next byte and handle crc.
+        else
+        {
+            //send the data
+            send_byte(data[i], BYTE);
+            //store the sent data into temp variable for crc calculation
+            crc_temp << 8;
+            crc_temp += data[i];
+            //increment array pointer
+            i++;
+            //wait until i increments and then check to see if 3 bytes have been sent
+            //i here is the actual count of bytes sent, not the array location that was just sent
+            //this also avoids sending a crc nibble after no data has been sent - can we figure logic for sending last crc if data not divisible by 3?
+            if( (i % 3) == 0)
+            {
+                //calculate and send crc
+                crc_value = calculate_crc(crc_temp);
+                send_byte(crc_value, NIBBLE);
+                //zero out crc temp variable
+                crc_temp = 0;
+            }
+        }
+    }
+    //output postamble
+    send_byte(post, BYTE);   
+    //turn off red led to show sending has finished
+    myled = 1;
+}
+
+void send_byte(unsigned char byte, int position)
 {
-    //not done(reset)
-    done = 0;
-    j = 128;
+    //starting bit position to send msb first
+    j = position;
 
     //output byte
-    while(!done) {
+    while(j>0)
+    {
         //start timer for clock
         t.start();
         //wait until the timer has reached the set time.
-        while(t.read_ms() < msecs) {
+        while(t.read_ms() < msecs)
+        {
             //extract data just before clock goes high
-            if(!clock_pin && skew_flag && t.read_ms() > sksecs) {
+            if(!clock_pin && skew_flag && t.read_ms() > sksecs)
+            {
                 //extract data bit
                 serial_out = (byte / j) % 2;
                 skew_flag = 0;
@@ -45,47 +115,23 @@
         clock_pin = !clock_pin;
         //reset skew flag
         skew_flag = 1;
-        //last preamble bit sent - reset/increment variables
-        if(j==0) {
-            done = 1;
-        }
     }
 }
 
-int main()
+unsigned char calculate_crc(int crc_bytes)
 {
-
-    //turn on red led to show programming has worked
-    myled = 0;
-    //initialize output pins
-    clock_pin = 0;
-    serial_out = 0;
-    //skew flag
-    skew_flag = 1;
-    //set timers
-    msecs = 1000;
-    sksecs = 800;
-
-    //output preamble
-    send_byte(pre);
-    //output address
-    send_byte(add);
-    //output data
-    i=0;
-    while(!sent) {
-        send_byte(data[i]);
-        //finished sending data
-        if(i>2) {
-            sent = 1;
-        }
-        i++;
-    }
-    //turn off red led to show sending has finished
-    myled = 1;
+    //temp variable
+    unsigned char temp
+    
+    //shift crc over 4 spots
+    (crc_bytes << 4);
+    
+    //return remainder
+    temp = crc_bytes % CRC;
+    return temp;     
 }
-
 //crc = x^4+x+1
-//put char data into unsigned short temp variable, then shift << 5. % this number by the decimal equivalent of binary representation of
-//the crc code and save and send it as a separate  5 bits. On the receive side save each byte in the temp character and then the next five
-//bytes in a temp variable - after receiving 13 bits stick data in unsigned short variable << 5 add the recieved 5 bits and then % by
-// the crc decimal equivalent, if that equals 0, save the temp character in the permanent character array and receive the next bits.
\ No newline at end of file
+//put char data into unsigned int temp variable, then shift << 4. % this number by the decimal equivalent of binary representation of
+//the crc code and save and send it as a separate  4 bits. On the receive side save each byte in the temp character and then the next five
+//bytes in a temp variable - after receiving 24 bits stick data in unsigned int variable << 4 add the recieved 4 bits and then % by
+//the crc decimal equivalent, if that equals 0, save the temp character in the permanent character array and receive the next bits.
\ No newline at end of file