RE: Writing a characteristic value from within the peripheral.

Marjeris Romero — Mon, 27 Apr 2020 14:04:11 GMT

Hi,

Sorry for the late reply.

For Question 1) What is the preferred call to update the characteristic value from within the peripheral itself?

If you only want to update the value, and not the send the update to a central, use sd_ble_gatts_value_set().

For Question 2) What is the recommended code for sending this update back to the central?

Use sd_ble_gatts_hvx(), this will both update the internal characteristic value in the SD, and send the update to the central. See this Message Sequence chart on the infocenter:
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.s132.api.v7.0.1%2Fgroup___b_l_e___g_a_t_t_s___h_v_n___m_s_c.html

Best regards,

Marjeris

RE: Writing a characteristic value from within the peripheral.

TCdeveloper — Wed, 15 Apr 2020 21:46:56 GMT

So I'll partially answer my own question after a bit of exploration. By explicitly setting the handle of the characteristic I want to send to the central, I can easily communicate which characteristic got modified. The handle was retrieved and stored at the time I set up the characteristic using the call to: sd_ble_gatts_characteristic_add();

        uint16_t len = 1;
        ble_gatts_hvx_params_t hvx_params;
        memset(&hvx_params, 0, sizeof(hvx_params));

        hvx_params.handle = char_handle;
        hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;
        hvx_params.offset = 0;
        hvx_params.p_len = &len;
        hvx_params.p_data = (uint8_t*) char_value;

sd_ble_gatts_hvx(p_our_service->conn_handle, &hvx_params);

I now pass in the "char_handle" and "char_value" that I want to NOTIFY the central about.

My question #1 still stands though on what is the preferred way to modify the characteristic at the peripheral. Currently, I am just directly modifying the location in memory (which is just a uint8_t variable) that I originally assigned to the characteristic value prior to initiation. However, I am still wondering if this might not be the best or proper way to inform the BLE stack that a value was changed.

Please advise. Thanks!