How to create characteristics with different UUIDs?

RE: How to create characteristics with different UUIDs?

Stefano1984 — Wed, 05 Jan 2022 08:46:41 GMT

Thank you very much Vidar.
You have been very kind.

Best regards.

RE: How to create characteristics with different UUIDs?

Vidar Berg — Wed, 05 Jan 2022 08:39:27 GMT

Hi,

Excellent! characteristic_add() is a helper function to simplify the process of adding new characteristics. If you look at the implementation of it, you can see that it calls the same Softdevice function in the end.

Regardless of which function you use, you have to set the .write_wo_resp or .write proprty to '1' to enable writes to the characteristic. Here it's how it's enabled for the NUS RX characteristic for reference:

RE: How to create characteristics with different UUIDs?

Stefano1984 — Tue, 04 Jan 2022 15:34:03 GMT

Hi Vidar,
thanks for your answer.
I was able to reach my goal thanks to your help.
I was able to add the characteristic but I can't read or write the characteristic. How do I enable reading and writing of the characteristic?
I used the ble_gatts_char_md_t structure with the sd_ble_gatts_characteristic_add function. See code below:

    uint32_t authentications_service_key_a_add(ble_cus_t * p_cus, const ble_cus_init_t * p_cus_init)
    {
        uint32_t            err_code;
        ble_gatts_char_md_t char_md;
        ble_gatts_attr_t    attr_char_value;
        ble_uuid_t          ble_uuid;
        ble_gatts_attr_md_t attr_md;

        memset(&char_md, 0, sizeof(char_md));

        char_md.char_props.read   = 1;
        char_md.char_props.write  = 0;
        char_md.char_props.notify = 0; 
        char_md.p_char_user_desc  = NULL;
        char_md.p_char_pf         = NULL;
        char_md.p_user_desc_md    = NULL;
        char_md.p_cccd_md         = NULL; 
        char_md.p_sccd_md         = NULL;
		
        ble_uuid.type = p_cus->uuid_type;
        ble_uuid.uuid = KEY_A_CHARACTERISTIC_UUID;

        memset(&attr_md, 0, sizeof(attr_md));

        attr_md.read_perm  = p_cus_init->custom_value_char_attr_md.read_perm;
        attr_md.write_perm = p_cus_init->custom_value_char_attr_md.write_perm;
        attr_md.vloc       = BLE_GATTS_VLOC_STACK;
        attr_md.rd_auth    = 0;
        attr_md.wr_auth    = 0;
        attr_md.vlen       = 0;

        memset(&attr_char_value, 0, sizeof(attr_char_value));

        attr_char_value.p_uuid    = &ble_uuid;
        attr_char_value.p_attr_md = &attr_md;
        attr_char_value.init_len  = sizeof(uint16_t);
        attr_char_value.init_offs = 0;
        attr_char_value.max_len   = sizeof(uint16_t);

        err_code = sd_ble_gatts_characteristic_add(p_cus->service_handle, &char_md,
                                                   &attr_char_value,
                                                   &p_cus->key_a_handles);

        return err_code;
    }

The characteristic_add function does not have a parameter of type ble_gatts_char_md_t. How can I do?
What is the difference between the characteristic_add function and the sd_ble_gatts_characteristic_add function?
Thanks so much.

RE: How to create characteristics with different UUIDs?

Vidar Berg — Tue, 04 Jan 2022 11:02:24 GMT

Hello,

I assume you are using the nRF5 SDK now? In that case, you will need to use sd_ble_uuid_vs_add() to add the base UUIDs for your characteristics. Below you can find a diff showing the changes I made to our UART service initialization (see UART/Serial Port Emulation over BLE) to make the RX characteristic have a different base UUID compared to the primary service.

diff --git a/ble_nus.c b/ble_nus.c
index ca77de6..b32772f 100644
--- a/ble_nus.c
+++ b/ble_nus.c
@@ -244,12 +244,16 @@ void ble_nus_on_ble_evt(ble_evt_t const * p_ble_evt, void * p_context)
     }
 }
 
+#define NUS_RX_BASE_UUID {0x80, 0xb9, 0xcb, 0x22, 0xd4, 0x47, 0x4b, 0x85, 0x8a, 0x4b, 0x88, 0x8e, 0x00, 0x00, 0x90, 0xf2}
+
 
 uint32_t ble_nus_init(ble_nus_t * p_nus, ble_nus_init_t const * p_nus_init)
 {
     ret_code_t            err_code;
     ble_uuid_t            ble_uuid;
+    uint8_t               uuid_tag;
     ble_uuid128_t         nus_base_uuid = NUS_BASE_UUID;
+    ble_uuid128_t         nus_rx_base_uuid = NUS_RX_BASE_UUID;
     ble_add_char_params_t add_char_params;
 
     VERIFY_PARAM_NOT_NULL(p_nus);
@@ -272,11 +276,15 @@ uint32_t ble_nus_init(ble_nus_t * p_nus, ble_nus_init_t const * p_nus_init)
                                         &p_nus->service_handle);
     /**@snippet [Adding proprietary Service to the SoftDevice] */
     VERIFY_SUCCESS(err_code);
+    
+
+    err_code = sd_ble_uuid_vs_add(&nus_rx_base_uuid, &uuid_tag);
+    VERIFY_SUCCESS(err_code);
 
     // Add the RX Characteristic.
     memset(&add_char_params, 0, sizeof(add_char_params));
     add_char_params.uuid                     = BLE_UUID_NUS_RX_CHARACTERISTIC;
-    add_char_params.uuid_type                = p_nus->uuid_type;
+    add_char_params.uuid_type                = uuid_tag;
     add_char_params.max_len                  = BLE_NUS_MAX_RX_CHAR_LEN;
     add_char_params.init_len                 = sizeof(uint8_t);
     add_char_params.is_var_len               = true;
diff --git a/sdk_config.h b/sdk_config.h
index 126fe8f..aa4b7ad 100644
--- a/sdk_config.h
+++ b/sdk_config.h
@@ -11466,7 +11466,7 @@
 
 // <o> NRF_SDH_BLE_VS_UUID_COUNT - The number of vendor-specific UUIDs. 
 #ifndef NRF_SDH_BLE_VS_UUID_COUNT
-#define NRF_SDH_BLE_VS_UUID_COUNT 1
+#define NRF_SDH_BLE_VS_UUID_COUNT 2
 #endif
 
 // <q> NRF_SDH_BLE_SERVICE_CHANGED  - Include the Service Changed characteristic in the Attribute Table.

Best regards,

Vidar