Decoding and making a Serial Number from STM32 96bit UID

gistfile1.txt

uint16_t snprint_stm32_serialno(char* p, uint16_t maxlen)
{
  uint32_t uid0 = *(uint32_t*) (UID_BASE);
  uint32_t uid1 = *(uint32_t*) (UID_BASE + 0x4);
  uint32_t uid2 = *(uint32_t*) (UID_BASE + 0x8);

  uint16_t n = 0;

  if (maxlen > 16)
  {
    p[0]= 'P';
    p[1]= 'G';
    p[2] = uid1 >> 8;
    p[3] = uid1 >> 16;
    p[4] = uid1 >> 24;
    p[5] = uid2;
    p[6] = uid2 >> 8;
    p[7] = uid2 >> 16;
    p[8] = uid2 >> 24;
    if (0 == isalnum((int) p[8]))
      p[8] = '-';

    n = 9;

    uint8_t wafer = uid1;
    uint8_t x_coord = uid0;
    uint8_t y_coord = uid0 >> 16;

    n += snprintf( &p[n], (maxlen - n), "%X%02X%02X", wafer, x_coord, y_coord);
    if (n > maxlen-1)
      n = maxlen-1;
    p[n]='\0';
  }

  return n;
}