BLE service with multiple characteristics(client/switch and bulb/server)

[davidm]

I am new to C programming and BLE in general.I am trying to create a service with two characteristics,(the application simply is a modification of BLE bulb and switch). How the original application work is, on the client/switch if you push button 1, it turns on the LED 3 on the server/bulb, and when you push button 2 it turns it off.So it is only one service and one characteristic. The client acts as central and server acts as a peripheral.

What I want is to add another characteristic so that If I push button 3 on the client to turn on  LED 4 on the server .(So in short button 1 will turn LED 3 on and button 3 will turn LED4 on).So I added additional characteristic on both server and client, but the problem is I don't know how to check/distinguish whether the incoming request  on the server is which characteristic.

Question

1. How do I inspect the incoming request whether is coming from characteristic 1 or 2 in the server's main.c  led_write_handler function?

Here is the code

static void led_write_handler(uint16_t conn_handle, ble_led_service_t * p_led_service, uint8_t led_state)
{
   //HERE I WANT TO DO IF THE REQUEST IS CHARACTERSIC 1 TURN LED3 AND IF 2 TURN LED 4
     //NRF_LOG_INFO("led handled %d", p_led_service->led_3_char_handles);
    if (led_state)
    {
        bsp_board_led_on(LIGHTBULB_LED3);
        NRF_LOG_INFO("Received LED ON!");
    }
    else
    {
        bsp_board_led_off(LIGHTBULB_LED3);
        NRF_LOG_INFO("Received LED OFF!");
    }
}

[Simon]

The reason you're not able to differentiate which characteristic was written inside led_write_handler(), is because none of the arguments give any information about it. 

The conn_handle and led_state does not tell you which characteristic was written to. You probably thought p_led_service would help you check what characteristic was written to, but this is not the case. It will be the same for both characteristics. Let me explain why:

• The function ble_led_service_on_ble_evt() is registered through the macro NRF_SDH_BLE_OBSERVER(), and it is associated with a context (the 4'th parameter)
• Each "observer" will then have a unique context associated with it, that is set once when registered
  • e.g. in your case the observer ble_led_service_on_ble_evt() is associated with a structure of type ble_led_service_t (please ask if you don't understand this and want me to elaborate)

One approach to differentiate between the characteristic, could be to check the uuid:

static void on_write(ble_led_service_t * p_led_service, ble_evt_t const * p_ble_evt)
{
    ble_gatts_evt_write_t const * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;
    
    uint16_t led_uuid = p_evt_write->uuid.uuid;
    
    if(.....){
        //Pass in uuid as an argument and take the appropriate action depending on that
        p_led_service->led_write_handler(p_ble_evt->evt.gap_evt.conn_handle, p_led_service, p_evt_write->data[0], led_uuid);
    }
}

Hope this helps.

Best regards,

Simon

[davidm]

Hi Simon thank you for taking a look.

So it seems like I just need to change the structure of led_write_handler() to accept additional uint16_t  in .h file  right?

[davidm]

Simon ,

I did what you advised but It seems like I am still experiencing the same issue. On main.c led_write_handler() the uuid always prints 65632 when I press button 2 or 3.

But on led_server_service.c on_write() uuid prints correctly 2 for button 2 and 3 for button 3 which are the uuid's I defined. So the issue is still on main.c led_write_handler()

static void led_write_handler(uint16_t conn_handle, ble_led_service_t * p_led_service, uint8_t led_state,uint16_t led_uuid)
{

     NRF_LOG_INFO("led uuid= %d",led_uuid); //Always prints 65632

    if (led_state)
    {
        bsp_board_led_on(LIGHTBULB_LED3);
        NRF_LOG_INFO("Received LED ON!");
    }
    else
    {
        bsp_board_led_off(LIGHTBULB_LED3);
        NRF_LOG_INFO("Received LED OFF!");
    }
}

[Simon]

I managed to make it work (led_write_handler prints correct uuid). Follow these steps exactly to make it work:

• Download SDK 15.3.0 and place it into an appropriate location
• Download the file two_char_leds.rar (which I have provided)
• For the peripheral example
  • Swap <..>two_char_leds\led_periph_server/ble_lbs.c and <..>two_char_leds\led_periph_server/ble_lbs.h with nRF5_SDK_15.3.0_59ac345\components\ble\ble_services\ble_lbs\ble_lbs.c and nRF5_SDK_15.3.0_59ac345\components\ble\ble_services\ble_lbs\ble_lbs.h 
  • Swap <..>\two_char_leds\led_periph_server\main.c with nRF5_SDK_15.3.0_59ac345\examples\ble_peripheral\ble_app_blinky\main.c
• For the central example
  • Swap <..>two_char_leds\led_central_client/ble_lbs_c.c and <..>two_char_leds\led_central_client/ble_lbs_c.h with nRF5_SDK_15.3.0_59ac345\components\ble\ble_services\ble_lbs_c\ble_lbs_c.c and nRF5_SDK_15.3.0_59ac345\components\ble\ble_services\ble_lbs_c\ble_lbs_c.h 
  • Swap <..>\two_char_leds\led_central_client\main.c with nRF5_SDK_15.3.0_59ac345\examples\ble_central\ble_app_blinky_c\main.c
• Connect two nRF52832 DK (that is what I tested with, but it should work with nRF52840 as well) to the computer and build and flash the ble_app_blinky_c example onto one of the boards and the ble_app_blinky example onto the other board
• Press button 1 on the central board, which should turn on/off  led 3 on the peripheral board
• Press button 2 on the central board, which should turn on/off led 4 on the peripheral board

two_char_leds.rar

Best regards,

Simon

[davidm]

Thank you, Simon, for sharing the code and taking the time to help. I am going to compare your code with mine. Right off the bat, I can see your advertising_init implementation is a little different from mine. But I am still continuing to look for discrepancies.