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/*A 'raw mode' data reader for the Parallax GPS receiver module #28146 (based on Polstar PMB-248)for use with the Baby Orangutan robot controller or with slight modifications, other Pololu orangutans(data stream is captured and parsed) [email protected]*/#define F_CPU 20000000UL // Baby Orangutan frequency (20MHz)#include <math.h> #include <avr/io.h>#include <util/delay.h> // uses F_CPU to achieve us and ms delays#include <pololu/orangutan.h>#include <stdlib.h>#include <string.h>#include <ctype.h>char gps[650]; // array to store $GPRMS string//format of Parallax GPS GPMRC string...//$GPMRC,HHMMSS,A,DDMM.MMMM,S,DDDMM.MMMM,S,KKK.K,HHH.H,DDMMYY,,,A*64<13>//0123456789012345678901234567890123456789012345678901234567890123456// 1 2 3 4 5 6 // $GPRMS string locations for following data items...int utc_hours=7, utc_minutes=9, utc_seconds=11, latitude=16, \ latitude_hemisphere=26, longitude=28, longitude_hemisphere=39, speed=41, \ heading=47, utc_day=53, utc_month=55, utc_year=57;void delayms(unsigned int time_ms) {for (unsigned int i = 0; i < time_ms; i++) _delay_ms(1);}//the following 4 debug functions flash an external LED I attached to #2 pwm motor port//because the built-in RED LED is not available when the UART is being usedvoid debug_port(unsigned char pwm){ OCR2A = 0; OCR2B = pwm;}void debug_init(){ TCCR2A = 0xF3; TCCR2B = 0x02; OCR2A = OCR2B = 0; DDRD |= (1 << PORTD3) | (1 << PORTD5) | (1 << PORTD6); DDRB |= (1 << PORTB3);}void debug_pulse_digit(int digit){ // pulse external led 1..10 times depending on value of digit // 1 -> 1 pulse; 2 -> 2 pulses; ... 9 -> 9 pulses; BUT 0 -> 10 pulses int counter, freq=75, delay=250; if(digit==0) digit = 10; // special case for 0 for(counter=1;counter<=digit;counter++) { debug_port(freq); delayms(delay); debug_port(0); delayms(delay); } delayms(1000);}void debug(float v){ // pulse 6 digits (hto.hto[-]) if negative, single pulse follows 6 pulse sequences // example output: -23.5 -> 023.500- -> 10 pulses, 2 pulses, 3 pulses, 5 pulses, 10 pulses, 10 pulses, 1 pulse int o,t,h,d,n=0; if(v<0){v=-v;n=1;} h=(int)(v/100);t=(int)((v-h*100)/10);o=(int)(v-t*10-h*100); debug_pulse_digit(h);debug_pulse_digit(t);debug_pulse_digit(o); d=(int)((v-h*100-t*10-o)*1000); // .hto -> hto. h=(int)(d/100);t=(int)((d-h*100)/10);o=(int)(d-t*10-h*100); debug_pulse_digit(h);debug_pulse_digit(t);debug_pulse_digit(o); if(n) debug_pulse_digit(1); // seventh pulse indicates negative delayms(1000); //pause between numbers}float get_gps(int request){ float r; if(request==utc_hours) r=(gps[utc_hours+0]-48)*10+(gps[utc_hours+1]-48); else if(request==utc_minutes) r=(gps[utc_minutes+0]-48)*10+(gps[utc_minutes+1]-48); else if(request==utc_seconds) r=(gps[utc_seconds+0]-48)*10+(gps[utc_seconds+1]-48); else if(request==latitude) { //accuracy: DDMM -- .MMMM ignored; minutes converted to decimal degrees r=(gps[latitude+0]-48)*10+(gps[latitude+1]-48)+(float)((gps[latitude+2]-48)*10+(gps[latitude+3]-48))/60; if(gps[latitude_hemisphere]=='S') r=-r; // apply sign } else if(request==longitude) { //accuracy: DDDMM -- .MMMM ignored; minutes converted to decimal degrees r=(gps[longitude+0]-48)*100+(gps[longitude+1]-48)*10+(gps[longitude+2]-48) \ +(float)((gps[longitude+3]-48)* 10+(gps[longitude+4]-48))/60; if(gps[longitude_hemisphere]=='W') r=-r; // apply sign } else if(request==speed) //fyi: mph = 6076/5280 * knots ~= 1.15*knots; speed below is in knots r=(gps[speed+0]-48)*100+(gps[speed+1]-48)*10+(gps[speed+2]-48)+(float)(gps[speed+3]-48)*0.1; else if(request==heading) r=(gps[heading+0]-48)*100+(gps[heading+1]-48)*10+(gps[heading+2]-48)+(float)(gps[heading+3]-48)*0.1; else if(request==utc_day) r=(gps[utc_day+0]-48)*10+(gps[utc_day+1]-48); else if(request==utc_month) r=(gps[utc_month+0]-48)*10+(gps[utc_month+1]-48); else if(request==utc_year) r=(gps[utc_year+0]-48)*10+(gps[utc_year+1]-48); else { debug(555); while(1); // error r = 0; } return r;}void init_gps() { //delayms(40000); //may require delay on cold start for gps module to acquire satellites debug_init(); serial_set_baud_rate(4800); char buf[1]; // request 1 char at a time from gps and copy to char array gps[] int gps_index, byte_count; for(gps_index=0;gps_index<=649;gps_index++) { serial_receive(buf,1); byte_count = serial_get_received_bytes(); while(byte_count == 0) byte_count = serial_get_received_bytes(); gps[gps_index]=buf[0]; } //find first instance of "$GPRMC" in gps[] char type[6] = "$GPRMC"; int type_matched = 0; int type_index; for(gps_index=0;gps_index<=644;gps_index++) { for(type_index=0; type_index<=5;type_index++) { if(gps[gps_index+type_index] == type[type_index]) type_matched=1; else { type_matched = 0; break; } } if(type_matched) break; } // upon exit type_matched==1 and gps_index <645 else error... if(!type_matched) { debug(555); // my arbitrary error code is 555 while(1); } // if we made it this far, everything ok //move data to start of array... for(int k=0;k<=65;k++) gps[k] = gps[gps_index+k];}int main(){ init_gps(); // at this point you may access gps values captured using 'get_gps(<keyword>)' // where <keyword> is any of: utc_hours, utc_minutes, utc_seconds, latitude, // longitude, speed, heading, utc_day, utc_month, utc_year // return type is float // note: // [-]longitude -> west of prime meridian, [-]latitude -> south of equator //example queries... //float lon = get_gps(longitude); //debug(lon); //debug(get_gps(latitude)); //delayms(5000); //debug(get_gps(utc_hours)); while(1); // wait forever return 0;}
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Topic: Parallax GPS module raw mode reader in C for Baby Orangutans (Read 3604 times)
