Write serial number

In the production line, the devices should be programmed with the identical firmware image. The object entry 1018 holds optionally a serial number which sould be unique for each device. We need a one-time programmable object entry.

Example Goal

The main idea is a manufacturer specific data type, which allows writing into a FLASH memory area if the current FLASH memory area is empty.

Object Type Idea

The main idea is an object entry, which is directly mapped to FLASH cells. The type checks on a write access for empty FLASH cells and allows writing with a FLASH write algorithm if FLASH cells are empty.

Object Entry Definitions

We define some manufacturer specific entries in the object dictionary:

Index Subindex Type Access Value Description
1018h 4 UNSIGNED32 Const FFFFFFFF Serial No.

The key to get the wanted functionality is the object type for the entry at subindex 4. This object type accepts a single permanent write access if the current value is 0xFFFFFFFF.

Implement Object Type

Lets implement the one time programmable (OTP) user type as shown in the CANopen Usage: User Object:

const uint32_t serialNo = 0xFFFFFFFFu;  /* locate this variable to FLASH and initialize with empty cell value */

const CO_OBJ_TYPE COTOtp = { 0, 0, 0, OtpWrite };

#define CO_TOTP ((CO_OBJ_TYPE*)&COTOtp)

The write function is called, when the CAN network writes to the related object entry via a SDO request. Now we want to allow the write algorithm for the constant FLASH value after a serial-no is written to the object entry at subindex 4.

int16_t OtpWrite(CO_OBJ *obj, struct CO_NODE_T *node, void *buf, uint32_t size)
  uint32_t value  = *((uint32_t *)buf);
  uint32_t serial = *((uinter_t *)obj->Data);
  CO_ERR   result = CO_ERR_TYPE_WR;

  if (serial == 0xFFFFFFFF) {
    /* call your hardware specific FLASH algorithm with
     * - start address in FLASH
     * - new serial value
     * - length of constant
    HwFlashWriteAlgorithm(obj->Data, value, 4);

  return result;

Implement Object Entries

We use our user type to define the calibration object entry:

const CO_OBJ ExampleObjDir[] = {
  { CO_KEY(0x1018, 4, CO_UNSIGNED32|CO_OBJ_D__R_), CO_TOTP, (uintptr_t)&serialNo },

Now we have a one time programmable object entry for the serial number. This concept shows how to integrate application specific logic to specific object entry access.