Return success/failure on BLE characteristic write (nRf52832)

[chandan]

Hi, I want to create one system. When master writes data of Nordic, I receive callback with BLE_GATTS_EVT_WRITE case. Here I want to write return to master with success/ failure based on write data, How we can control of write success/failure from Nordic?

Thanks

[Andy]

Use writes with authorization. There you have a kind of built-in reply mechanism where you can specify whether the operation (read or write) was successful or not. I would link the message sequence chart for authorized writes here, but the infocenter appears to be down.

[Einar Thorsrud]

The Infocenter is up now. Here is the link to the MSC for GATTS Write Request with Authorization.

[chandan]

I solved that, One issue I am facing now. When should i trigger read of write values from master, In case BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST ?

[Andy]

Yes, you could have something like this:

case BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST:
	switch (p_ble_evt->evt.gatts_evt.params.authorize_request.type) {
		case BLE_GATTS_AUTHORIZE_TYPE_READ:
    		on_read_auth(p_ble_evt);
    		break;
		case BLE_GATTS_AUTHORIZE_TYPE_WRITE:
    		on_write_auth(p_ble_evt);
    		break;
	}
	break;

[chandan]

Yes, I am doing kinda similar. Calling on_disp_write, but if condition is failing. Handlers values are different.

static void on_disp_write(ble_cus_t *p_cus, ble_evt_t const *p_ble_evt) {

  ble_gatts_evt_write_t const *p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;
  ble_gatts_rw_authorize_reply_params_t auth_reply = {0};
  auth_reply.type = BLE_GATTS_AUTHORIZE_TYPE_WRITE;

  // Custom Value Characteristic Written to.
  if (p_evt_write->handle == p_cus->custom_value_handles.value_handle) {
  }
}

[Andy]

I don't know where you're getting that value handle from. You must be setting it wrong if you're having problems with that.

[chandan]

When I tried same without writes with authorization, same part is working perfect. Can you please share on_write_auth for reference ?

[Andy]

static void on_write_auth(ble_evt_t const * p_ble_evt) {
	ret_code_t err_code = NRF_SUCCESS;
	ble_gatts_rw_authorize_reply_params_t auth_reply;
	uint8_t * p_data = (uint8_t *)(p_ble_evt->evt.gatts_evt.params.authorize_request.request.write.data);
	uint16_t len = p_ble_evt->evt.gatts_evt.params.authorize_request.request.write.len;

	uint16_t char_UUID = p_ble_evt->evt.gatts_evt.params.authorize_request.request.write.uuid.uuid;
	uint16_t offset = p_ble_evt->evt.gatts_evt.params.authorize_request.request.write.offset;

	err_code = parse_ble_data(char_UUID, p_data, len, offset);

	if (err_code == NRF_SUCCESS) {
		auth_reply.type = BLE_GATTS_AUTHORIZE_TYPE_WRITE;
		auth_reply.params.write.gatt_status = BLE_GATT_STATUS_SUCCESS;
		auth_reply.params.write.update = 1;
		auth_reply.params.write.len = len;
		auth_reply.params.write.offset = offset;
		auth_reply.params.write.p_data = p_data;
	} else {
		auth_reply.type = BLE_GATTS_AUTHORIZE_TYPE_WRITE;
		auth_reply.params.write.gatt_status = BLE_GATT_STATUS_ATTERR_WRITE_NOT_PERMITTED;
	}
	err_code = sd_ble_gatts_rw_authorize_reply(p_ble_evt->evt.gatts_evt.conn_handle, &auth_reply);
	APP_ERROR_CHECK(err_code);
}