/* Checksum computing for DG834
 *
 * Checksum is computed by adding bytes from 0 to 0x3dfffb.
 * The 16 bit sum must be equal to the little endian 16 bit word stored at
 * 0x3dfffc-03dfffd.
 */

#include <stdlib.h>
#include <stdio.h>

/* load a file in memory */
static
int read_file(const char *filename, long *size, void **buffer)
{
  FILE *fp;

  /* open file for reading */
  fp = fopen(filename, "rb");
  if (fp == NULL) {
    fprintf(stderr, "Could not open <%s>\n", filename);
    return 1;
  }

  /* compute file size */
  if (fseek(fp, 0, SEEK_END) != 0) {
    fprintf(stderr, "Could not open <%s>\n", filename);
    fclose(fp);
    return 1;
  }
  *size = ftell(fp);
  fseek(fp, 0, SEEK_SET);
  if (*size == -1) {
    fprintf(stderr, "Could not get size of file <%s>\n", filename);
    fclose(fp);
    return 1;
  }

  /* allocate memory to read the file */
  *buffer = malloc(*size);
  if (*buffer == NULL) {
    fprintf(stderr, "Could not alloc mem to read file <%s>\n", filename);
    fclose(fp);
    return 1;
  }

  /* read the file */
  if (fread(*buffer, 1, *size, fp) != *size) {
    fprintf(stderr, "Could not read file <%s>\n", filename);
    fclose(fp);
    return 1;
  }

  /* we're done */
  fclose(fp);

  return 0;
}

/* read 8 bit */
static
unsigned short read_8(unsigned char *mem, unsigned int addr)
{
  return mem[addr];
}

/* read a 16 bit word in little endian */
static
unsigned short read_16l(unsigned char *mem, unsigned int addr)
{
  return mem[addr] | (mem[addr+1] << 8);
}

/* compute check sum */
static
unsigned short compute_checksum(unsigned char *mem)
{
  unsigned int   addr;
  unsigned short word;
  unsigned short checksum;

  checksum = 0;
  for (addr = 0; addr < 0x3dfffc; addr++) {
    word = read_8(mem, addr);
    checksum += word;
  }

  return checksum;
}

int main(int argc, const char *argv[])
{
  const char     *filename;
  long            size;
  void           *mem;
  unsigned short  checksum;

  /* command line */
  if (argc != 2) {
    fprintf(stderr, "Usage: %s firmware\n", argv[0]);
    return 1;
  }
  filename = argv[1];

  /* read file in memory */
  if (read_file(filename, &size, &mem) != 0) {
    return 2;
  }
  if (size != 0x3e0000) {
    fprintf(stderr, "File <%s> has wrong size\n", filename);
    return 3;
  }

  /* compute checksum */
  checksum = compute_checksum(mem);

  /* check it's OK */
  printf("Computed checksum is %04x\n", checksum);
  printf("Stored checksum is %04x\n", read_16l(mem, 0x3dfffc));
  if (checksum != read_16l(mem, 0x3dfffc)) {
    printf("WARNING:  checksum does not match!\n");
  }

  /* time to leave */
  free(mem);

  return 0;
}