cm_nmea_decoder/cm_nmea_decoder.c

/*
 * cm_nmea_decoder.c
 *
 *  Created on: 26 Jun 2025
 *      Author: Christian Lind Vie Madsen
 */

#include "cm_nmea_decoder.h"
#include <stdlib.h>
#include <string.h>

static int findFirstChar(const char *str, const char Ch){

	for(int i = 0; ; i++){

		if(str[i] == Ch) return i;
		if(str[i] == '\0') return -1;
	}

	return -1;
}

static int isPeriodInLine(char *str){

	int i = 0;

	while((str[i] != '.') && (str[i] != '\0') && (str[i] != ',')) i++;

	if(str[i] == '\0' || str[i] == ',') return -1;

	return i;
}

static int moveToNextLine(char **str){

	// Check if moved to next line or past the string.
	while((**str != ',') && (**str != '\0')){

		// Count pointer up because we didnt came across ',' or end
		(*str)++;

	}

	// Throw error code if we found end and not a ','
	if(**str == '\0') return -1;

	// Move past ','
	(*str)++;

	return 1;

}

static int decodeIntIntoStruct(uint8_t *inst, char *str, nmea_field_type type){

    int isPeriod = isPeriodInLine(str);
    uint8_t next_val = 0;

    int lineEnd = findFirstChar(str, ',');
    if (lineEnd < 0) return -1; // error check
    str[lineEnd] = '\0';

    switch (type) {
        case NMEA_FIELD_UINT8_T:
        	*((uint8_t*)inst) = (uint8_t)atoi(str);
        	next_val = sizeof(uint8_t);
            break;
        case NMEA_FIELD_INT8_T:
        	*((int8_t*)inst) = (int8_t)atoi(str);
        	next_val = sizeof(int8_t);
            break;
        case NMEA_FIELD_UINT16_T:
        	*((uint16_t*)inst) = (uint16_t)(isPeriod != -1 ? atoi(str) * 10000 + atoi(str + isPeriod + 1) : atoi(str));
        	next_val = sizeof(uint16_t);
            break;
        case NMEA_FIELD_INT16_T:
        	*((int16_t*)inst) = (int16_t)(isPeriod != -1 ? atoi(str) * 10000 + atoi(str + isPeriod + 1) : atoi(str));
        	next_val = sizeof(int16_t);
            break;
        case NMEA_FIELD_UINT32_T:
        	*((uint32_t*)inst) = (uint32_t)(isPeriod != -1 ? atoi(str) * 10000 + atoi(str + isPeriod + 1) : atoi(str));
        	next_val = sizeof(uint32_t);
            break;
        case NMEA_FIELD_INT32_T:
        	*((int32_t*)inst) = (int32_t)(isPeriod != -1 ? atoi(str) * 10000 + atoi(str + isPeriod + 1) : atoi(str));
        	next_val = sizeof(int32_t);
        	//printf("val: %d \r\n", *((int32_t*)inst));
            break;

        default:
        	break;
    }

    str[lineEnd] = ','; // Restore

    return next_val;
}


static int storeValIntoStruct(uint8_t *inst, char *str, nmea_field_type type){



	if((type >= NMEA_FIELD_UINT8_T) && (type <= NMEA_FIELD_INT32_T)){

		return decodeIntIntoStruct(inst, str, type);
	}

	if(type == NMEA_FIELD_CHAR_T){

		char *p = (void*)inst;

		*p = *str;
	}




	return 1;



}

static int sNMEA_decode(cm_nmea_msg_t *inst, char *str, int sentence_idx){

	nmea_field_desc_t *p = &nmea_sentences[sentence_idx];

	uint8_t *dst = (void*)inst;

	int next_val = 0;

	moveToNextLine(&str);

	printf("%s \r\n", str);

	for(int i = 0; i < p->field_type_size; i++){

		next_val = storeValIntoStruct(dst, str, p->field_type[i]);

		if(next_val == -1) return next_val;

		dst += next_val;


	    if (i < p->field_type_size - 1 && moveToNextLine(&str) == -1)
	        return 0;

	}

	printf("lat: %d, lat_dir: %c, lon: %d, lon_dir: %c, utc: %d", inst->msg.gpgll.latitude, inst->msg.gpgll.lat_dir, inst->msg.gpgll.longitude, inst->msg.gpgll.lon_dir, inst->msg.gpgll.utc_time);


	return 0;
}

static int sNMEA_getMsgType(char *str){

	for(int i = 0; i < (sizeof(nmea_sentences) / sizeof(nmea_sentences[0])); i++){

		if(strncmp(nmea_sentences[i].nmea_sentence, str, 6) == 0) return nmea_sentences[i].nmea_sentence_type;
	};

	return -1;
}

int cm_nmea_characterDecode(char in){

return 0;

}

// This function returns the message type, so the user knows which message has been decoded!
int cm_nmea_stringDecode(cm_nmea_msg_t *inst, char *str){

	// Find which type of message we need to decode.
	int nmea_msg_idx = sNMEA_getMsgType(str);

	// Check if we found a valid NMEA message.
	if(nmea_msg_idx == -1) return nmea_msg_idx;

	// Decode message:
	sNMEA_decode(inst,str,nmea_msg_idx);


	return nmea_msg_idx;

}