/* crc-calc.c - Calculate and set a CRC of a soil sensor combined (main + bootloader)
 * firmware image. The path to the firmware image is passed as the first 
 * command-line argument. */
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

/* Calculate CRC of a Sense/Net packet. packet[0] is the header.
 * If this function is computed over a whole packet, including the
 * CRC at the end, a return value of 0 indicates a valid packet. */
uint16_t calc_crc(uint8_t *packet, int packet_length){
	uint16_t remainder = 0xFFFF;
	
	for (int i = 0; i < packet_length; i++){
		remainder ^= packet[i] << 8;
		for (int bit = 8; bit > 0; bit--){
			if (remainder & 0x8000){
				remainder = (remainder << 1) ^ 0x1021;
			} else {
				remainder = (remainder << 1);
			}
		}
	}
	return remainder;
}

/* Compute and set the overall CRC of the whole main firmware flash space.
 * A CRC is first computed for each set of six flash pages, then an
 * overall CRC is computed from those. */
void calc_flash_crc(uint8_t *flash){
	uint8_t sixpage_crcs[64]; /* CRCs of each set of six pages. */
	uint16_t temp;
	
	for(int i=0; i<32; i++){
		if(31 == i){
			/* Exclude the last two bytes of the last page, 
			 * as they contain the overall CRC. */
			temp = calc_crc(flash + (i * 192), 190);
			sixpage_crcs[i * 2] = temp & 0xFF;
			sixpage_crcs[(i * 2) + 1] = (temp >> 8) & 0xFF;
		} else {
			temp = calc_crc(flash + (i * 192), 192);
			sixpage_crcs[i * 2] = temp & 0xFF;
			sixpage_crcs[(i * 2) + 1] = (temp >> 8) & 0xFF;
		}
	}
	temp = calc_crc((uint8_t *) sixpage_crcs, 64);
	flash[6142] = temp & 0xFF;
	flash[6143] = (temp >> 8) & 0xFF;
}

int main(int argc, char *argv[]){
	if(argc != 2){
		fprintf(stderr, "crc-calc: error: expected the firmware image path as the only command-line argument.\n");
		return -1;
	}
	
	FILE *fwfile;
	fwfile = fopen(argv[1], "r+");
	if(NULL == fwfile){
		fprintf(stderr, "crc-calc: error: could not open firmware file %s\n", argv[1]);
		perror(NULL);
		return -1;
	}
	
	/* Check that the file isn't too large. */
	fseek(fwfile, 0, SEEK_END);
	int fwsize = ftell(fwfile);
	rewind(fwfile);
	if(fwsize > 8192){
		fprintf(stderr, "crc-calc: error: firmware file %s too large\n", argv[1]);
		return -1;
	}
	if(fwsize < 6144){
		fprintf(stderr, "crc-calc: error: firmware file %s too small\n", argv[1]);
		return -1;
	}
	
	/* Load firmware into memory. */
	char *fwbuf = malloc(6144);
	if(NULL == fwbuf){
		fprintf(stderr, "crc-calc: error: malloc failure.");
		return -1;
	}

	if(6144 != fread(fwbuf, 1, 6144, fwfile)){
		fprintf(stderr, "crc-calc: error: could not read firmware file.\n");
		perror("calc-crc");
		return -1;
	}
	rewind(fwfile);
	
	calc_flash_crc((uint8_t *) fwbuf);
	if(6144 != fwrite(fwbuf, 1, 6144, fwfile)){
		fprintf(stderr, "crc-calc: error: could not write firmware file.\n");
		perror("calc-crc");
		return -1;
	}
	
	fclose(fwfile);
	free(fwbuf);
	return 0;
}