Differentiate between different writes

[danbujak]

I have a few characteristics under a service, and I'm trying to store the value if any of these characteristics is written to. However I run into an issue where if I enable services on the Master Control Panel, my code thinks that the value of the characteristic is being written.

How do I differentiate between a write to the actual data value of my characteristic and whatever the master control panel is doing when I enable services?

static void ble_evt_dispatch(ble_evt_t * p_ble_evt)
{
    dm_ble_evt_handler(p_ble_evt);
    on_ble_evt(p_ble_evt);
    check_status(p_ble_evt);
}

static void check_status(ble_evt_t * p_ble_evt){	
    
    ble_gatts_evt_write_t *p_evt_write = &p_ble_evt -> evt.gatts_evt.params.write;
    
    switch (p_ble_evt -> header.evt_id)
        {
        case BLE_GATTS_EVT_WRITE:
            if (p_evt_write -> context.srvc_uuid.uuid == DEVICE_STATUS_SERVICE_UUID){
                /* If mode characteristic was written to update the status value */
                if (p_evt_write -> context.char_uuid.uuid == DEVICE_STATUS_MODE_UUID){
                    m_status.mode = p_evt_write -> data[0];
                }
                /* If datarate characteristic was written to update the status value */
                else if (p_evt_write -> context.char_uuid.uuid == DEVICE_STATUS_DATARATE_UUID){
                    m_status.datarate = p_evt_write -> data[0];
                }
                advertising_init();     /* Update advertising data with new mode and datarate */
            }
        break;
    }
}

Once I enable services, both m_status.mode and m_status.datarate are set to 0x03. If I write to both of these characteristics after enabling services the correct values are written to them. But for example if I only modify one, the other one will have 0x03 stored in it still (even though the attribute is storing 0x0).

[wlgrd]

MCP is doing a write to CCCD to enable services, which will enter this case, and you are doing advertising init no matter what is written to.

[danbujak]

Yes that's the behaviour I see, but I'd like to know how to differentiate between a write to the value vs a write to some other parameter. I intentionally do advertising init when anything contained in the DEVICE_STATUS_SERVICE_UUID service is written to.

[wlgrd]

I see in the heart rate service example, in hrs.c ->

static void on_write(ble_hrs_t * p_hrs, ble_evt_t * p_ble_evt)
{
ble_gatts_evt_write_t * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;

if (p_evt_write->handle == p_hrs->hrm_handles.cccd_handle)
{
    on_hrm_cccd_write(p_hrs, p_evt_write);
}
}

Could you get your service structure passed into your check_status()?

[danbujak]

I'm not sure how I could do this. I'm calling check_status() from ble_evt_dispatch()

[wlgrd]

When you initialize your service, you pass in this structure, like in hrs;

 err_code = ble_hrs_init(&m_hrs, &hrs_init);

That m_hrs struct is also passed from ble_evt_dispatch()

static void ble_evt_dispatch(ble_evt_t * p_ble_evt)
{
dm_ble_evt_handler(p_ble_evt);
ble_hrs_on_ble_evt(&m_hrs, p_ble_evt);
(...)

Maybe you should post more of your code if this doesn't get you on your way :)