Kevin Anderson / Mbed 2 deprecated DataCommFreedom

Using FRDM Board to output data and a clock for communications example.

Dependencies:   mbed

main.cpp@11:aa30552269b2, 2015-04-30 (annotated)

Committer:
askksa12543
Date:
Thu Apr 30 14:05:24 2015 +0000
Revision:
11:aa30552269b2
Parent:
10:90cc064f7082 
crc fixed

Who changed what in which revision?

UserRevisionLine numberNew contents of line
askksa12543 8:2b61de165543 1 //project to include preamble, addressing, post amble, crc error control.
askksa12543 2:11f32d8cfa11 2
askksa12543 9:77ae456366f7 3 //after sending - set clock to 0, set timer and check clock pin - if clock pin goes high read in response - 4 bit ack?
askksa12543 9:77ae456366f7 4
askksa12543 0:7c7f4b30d64f 5 #include "mbed.h"
askksa12543 0:7c7f4b30d64f 6 #include "stdio.h"
askksa12543 0:7c7f4b30d64f 7
askksa12543 8:2b61de165543 8 #define MAX 100 //set the max size of the character data storage array
askksa12543 8:2b61de165543 9 #define BYTE 128
askksa12543 10:90cc064f7082 10 #define NIBBLE 8 //used to set binary position of msb
askksa12543 3:027d30718bbc 11 #define PREAMBLE 0x7E //preamble of 01111110
askksa12543 8:2b61de165543 12 #define POSTAMBLE 0x81 //postamble of 10000001
askksa12543 8:2b61de165543 13 //addressing 1st 4 bits indicate the network, 2nd 4 bits indicate the station id
askksa12543 8:2b61de165543 14 #define ADDRESS 0x12 //address of 00010010 network = 1, station id = 2
askksa12543 8:2b61de165543 15 #define BROADCAST 0x00 //broadcast address of 00000000
askksa12543 8:2b61de165543 16 #define MULTICAST 0x10 //broadcast to only network 1, all stations
askksa12543 8:2b61de165543 17 #define CRC 0x13 //crc of 10011 or x^4+x+1 or crc-5
askksa12543 2:11f32d8cfa11 18
askksa12543 2:11f32d8cfa11 19 DigitalOut myled(LED1); // red led on board
askksa12543 8:2b61de165543 20 DigitalOut clock_pin(D8), serial_out(D7); //send clock pulse and data
askksa12543 0:7c7f4b30d64f 21 Timer t; //timer for controlling the clock and data skew
askksa12543 2:11f32d8cfa11 22 int msecs, sksecs; //clock time needed for data transfer and skew time
askksa12543 8:2b61de165543 23 unsigned char pre = PREAMBLE, add = BROADCAST, post = POSTAMBLE, crc_value = 0; //protocol overhead
askksa12543 8:2b61de165543 24 unsigned char data[MAX] = "Hi Kyle!\n"; //data output
askksa12543 8:2b61de165543 25 int crc_temp = 0; //temporary crc variable
askksa12543 8:2b61de165543 26 unsigned char sent = 0, i = 0, j = 0, skew_flag; //increment variables and flags
askksa12543 8:2b61de165543 27
askksa12543 8:2b61de165543 28 //function prototypes
askksa12543 8:2b61de165543 29 //send a byte of data, for preamble, postamble, address, and data with BYTE, crc with NIBBLE
askksa12543 8:2b61de165543 30 void send_byte(unsigned char byte, int position);
askksa12543 8:2b61de165543 31
askksa12543 8:2b61de165543 32 //calculate the crc value to send.
askksa12543 8:2b61de165543 33 unsigned char calculate_crc(int crc_bytes);
askksa12543 8:2b61de165543 34
askksa12543 8:2b61de165543 35
askksa12543 8:2b61de165543 36 int main()
askksa12543 8:2b61de165543 37 {
askksa12543 8:2b61de165543 38
askksa12543 8:2b61de165543 39 //turn on red led to show programming has worked
askksa12543 8:2b61de165543 40 myled = 0;
askksa12543 8:2b61de165543 41 //initialize output pins
askksa12543 8:2b61de165543 42 clock_pin = 0;
askksa12543 8:2b61de165543 43 serial_out = 0;
askksa12543 8:2b61de165543 44 //skew flag
askksa12543 8:2b61de165543 45 skew_flag = 1;
askksa12543 8:2b61de165543 46 //set timers
askksa12543 8:2b61de165543 47 msecs = 100;
askksa12543 8:2b61de165543 48 sksecs = 80;
askksa12543 0:7c7f4b30d64f 49
askksa12543 8:2b61de165543 50 //output preamble
askksa12543 8:2b61de165543 51 send_byte(pre, BYTE);
askksa12543 8:2b61de165543 52 //output address
askksa12543 8:2b61de165543 53 send_byte(add, BYTE);
askksa12543 8:2b61de165543 54 //output data
askksa12543 8:2b61de165543 55 while(!sent)
askksa12543 8:2b61de165543 56 {
askksa12543 8:2b61de165543 57 //finished sending data when string termination found
askksa12543 8:2b61de165543 58 if(data[i] == '\n')
askksa12543 8:2b61de165543 59 {
askksa12543 8:2b61de165543 60 sent = 1;
askksa12543 9:77ae456366f7 61 //pad out sent data with 0's so crc is sent for all data.
askksa12543 9:77ae456366f7 62 while( (i%3) != 0)
askksa12543 9:77ae456366f7 63 {
askksa12543 9:77ae456366f7 64 //pad data with 0's
askksa12543 9:77ae456366f7 65 data[i] = 0x00;
askksa12543 9:77ae456366f7 66 send_byte(data[i], BYTE);
askksa12543 9:77ae456366f7 67 //store 0's into temp variable for crc calculation
askksa12543 9:77ae456366f7 68 crc_temp <<= 8;
askksa12543 9:77ae456366f7 69 crc_temp += data[i];
askksa12543 9:77ae456366f7 70 i++;
askksa12543 9:77ae456366f7 71 }
askksa12543 9:77ae456366f7 72 //calculate and send crc
askksa12543 9:77ae456366f7 73 crc_value = calculate_crc(crc_temp);
askksa12543 9:77ae456366f7 74 send_byte(crc_value, NIBBLE);
askksa12543 8:2b61de165543 75 }
askksa12543 8:2b61de165543 76 //string still has data send next byte and handle crc.
askksa12543 8:2b61de165543 77 else
askksa12543 8:2b61de165543 78 {
askksa12543 8:2b61de165543 79 //send the data
askksa12543 8:2b61de165543 80 send_byte(data[i], BYTE);
askksa12543 8:2b61de165543 81 //store the sent data into temp variable for crc calculation
askksa12543 9:77ae456366f7 82 crc_temp <<= 8;
askksa12543 8:2b61de165543 83 crc_temp += data[i];
askksa12543 8:2b61de165543 84 //increment array pointer
askksa12543 8:2b61de165543 85 i++;
askksa12543 8:2b61de165543 86 //wait until i increments and then check to see if 3 bytes have been sent
askksa12543 8:2b61de165543 87 //i here is the actual count of bytes sent, not the array location that was just sent
askksa12543 9:77ae456366f7 88 //this also avoids sending a crc nibble after no data has been sent
askksa12543 8:2b61de165543 89 if( (i % 3) == 0)
askksa12543 8:2b61de165543 90 {
askksa12543 8:2b61de165543 91 //calculate and send crc
askksa12543 8:2b61de165543 92 crc_value = calculate_crc(crc_temp);
askksa12543 8:2b61de165543 93 send_byte(crc_value, NIBBLE);
askksa12543 8:2b61de165543 94 //zero out crc temp variable
askksa12543 8:2b61de165543 95 crc_temp = 0;
askksa12543 9:77ae456366f7 96 crc_value = 0;
askksa12543 8:2b61de165543 97 }
askksa12543 8:2b61de165543 98 }
askksa12543 8:2b61de165543 99 }
askksa12543 8:2b61de165543 100 //output postamble
askksa12543 8:2b61de165543 101 send_byte(post, BYTE);
askksa12543 8:2b61de165543 102 //turn off red led to show sending has finished
askksa12543 8:2b61de165543 103 myled = 1;
askksa12543 8:2b61de165543 104 }
askksa12543 8:2b61de165543 105
askksa12543 8:2b61de165543 106 void send_byte(unsigned char byte, int position)
n02655194 6:4ef63169c970 107 {
askksa12543 8:2b61de165543 108 //starting bit position to send msb first
askksa12543 8:2b61de165543 109 j = position;
n02655194 6:4ef63169c970 110
n02655194 6:4ef63169c970 111 //output byte
askksa12543 8:2b61de165543 112 while(j>0)
askksa12543 8:2b61de165543 113 {
askksa12543 3:027d30718bbc 114 //start timer for clock
askksa12543 3:027d30718bbc 115 t.start();
askksa12543 3:027d30718bbc 116 //wait until the timer has reached the set time.
askksa12543 8:2b61de165543 117 while(t.read_ms() < msecs)
askksa12543 8:2b61de165543 118 {
askksa12543 3:027d30718bbc 119 //extract data just before clock goes high
askksa12543 8:2b61de165543 120 if(!clock_pin && skew_flag && t.read_ms() > sksecs)
askksa12543 8:2b61de165543 121 {
askksa12543 3:027d30718bbc 122 //extract data bit
n02655194 6:4ef63169c970 123 serial_out = (byte / j) % 2;
askksa12543 3:027d30718bbc 124 skew_flag = 0;
askksa12543 3:027d30718bbc 125 j /= 2; //decrement j to get to next bit location
askksa12543 3:027d30718bbc 126 }
askksa12543 3:027d30718bbc 127 }
askksa12543 3:027d30718bbc 128 //stop and reset the timer
askksa12543 3:027d30718bbc 129 t.stop();
askksa12543 3:027d30718bbc 130 t.reset();
askksa12543 3:027d30718bbc 131 //switch clock signal
askksa12543 3:027d30718bbc 132 clock_pin = !clock_pin;
askksa12543 3:027d30718bbc 133 //reset skew flag
askksa12543 3:027d30718bbc 134 skew_flag = 1;
n02655194 6:4ef63169c970 135 }
n02655194 6:4ef63169c970 136 }
n02655194 6:4ef63169c970 137
askksa12543 8:2b61de165543 138 unsigned char calculate_crc(int crc_bytes)
n02655194 6:4ef63169c970 139 {
askksa12543 8:2b61de165543 140 //temp variable
askksa12543 9:77ae456366f7 141 unsigned char temp;
askksa12543 10:90cc064f7082 142 //start at 2^25 / used to decrement through the bit places of the crc integer
askksa12543 10:90cc064f7082 143 int j = 16777216;
askksa12543 8:2b61de165543 144
askksa12543 10:90cc064f7082 145 //shift crc over 4 spots
askksa12543 10:90cc064f7082 146 crc_bytes <<= 4;
askksa12543 10:90cc064f7082 147
askksa12543 10:90cc064f7082 148 //initialize temp variable to the 8 msb from crc_bytes, then XOR with CRC constant
askksa12543 10:90cc064f7082 149 temp = crc_bytes / j;
askksa12543 10:90cc064f7082 150 temp ^= CRC;
askksa12543 10:90cc064f7082 151 //decrement j
askksa12543 11:aa30552269b2 152 j /= 2;
askksa12543 8:2b61de165543 153
askksa12543 10:90cc064f7082 154 //crc loop - shift in each bit position and xor with CRC constant
askksa12543 10:90cc064f7082 155 while(j>0)
askksa12543 10:90cc064f7082 156 {
askksa12543 10:90cc064f7082 157 //left shift current temp value
askksa12543 10:90cc064f7082 158 temp <<= 1;
askksa12543 10:90cc064f7082 159 //shift in new bit from crc bytes
askksa12543 10:90cc064f7082 160 temp += (crc_bytes / j) % 2;
askksa12543 10:90cc064f7082 161 //xor with crc constant
askksa12543 10:90cc064f7082 162 temp ^= CRC;
askksa12543 10:90cc064f7082 163 //decrement j
askksa12543 11:aa30552269b2 164 j /= 2;
askksa12543 10:90cc064f7082 165 }
askksa12543 10:90cc064f7082 166
askksa12543 10:90cc064f7082 167 //mask out 4 msb bits and return just the 4 bit CRC remainder
askksa12543 10:90cc064f7082 168 temp = temp & 0x0F;
askksa12543 10:90cc064f7082 169
askksa12543 8:2b61de165543 170 return temp;
askksa12543 1:4c0c28cc2b2c 171 }
askksa12543 4:39a777388acd 172 //crc = x^4+x+1
askksa12543 8:2b61de165543 173 //put char data into unsigned int temp variable, then shift << 4. % this number by the decimal equivalent of binary representation of
askksa12543 8:2b61de165543 174 //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
askksa12543 8:2b61de165543 175 //bytes in a temp variable - after receiving 24 bits stick data in unsigned int variable << 4 add the recieved 4 bits and then % by
askksa12543 8:2b61de165543 176 //the crc decimal equivalent, if that equals 0, save the temp character in the permanent character array and receive the next bits.