Problem with sd_ble_gatts_hvx without notifications enabled

[Gauti]

Hi there!

I am trying to add custom UUID's for my BLE application. I have a custom service which has 2 RX and 3 TX characteristics.

I have a situation where the Android APP that I am using doesn't notify. Because of this I am not able to write my data into one of the TX characteristics to transmit data to the mobile.

This results in sd_ble_gatts_hvx() returning error code as 8 - INVALID STATE.

As a workaround I added the following:

    case BLE_GAP_EVT_CONNECTED:
    	gu16_connhandle = lsp_ble_evt->evt.gap_evt.conn_handle;
    	errcode = sd_ble_gatts_sys_attr_set(gu16_connhandle, NULL, 0, 0);

As this did not work, I tried doing the following too:

    	lu16ar_Buffer[0] = 16;      // cccd handle
    	lu16ar_Buffer[1] = 2;       // cccd attribute size = 2
    	lu16ar_Buffer[2] = 1;       // 1 = enable notifications
    	lu16ar_Buffer[3] = 0xCACD;  // CRC-CCITT (0xFFFF)
    	lu32_errcode = sd_ble_gatts_sys_attr_set(gu16_connhandle, (u8*)lu16ar_Buffer, 8, 0);

Inspite of doing the above, I did not have any luck transmitting the BLE data that I intend to.

Is there any way that I can transmit (write in the characteristics) without the notification being enabled from the Android APP?

I am using SDK 12.1

Thanks in advance!

[Jørgen Holmefjord]

Hi,

If notifications is not enabled, you should use sd_ble_gatts_value_set() to set the value of the characteristics. The other side then needs to read the characteristics to get the new value.

Best regards,

Jørgen

[Gauti]

Hi, Thanks for your reply! I did add the below piece of code in on_connect() with no luck:

uint32_t          err_code;
uint8_t           default_protocol_mode;
ble_gatts_value_t gatts_value;

lsp_nus->conn_handle = lsp_ble_evt->evt.gap_evt.conn_handle;

if (lsp_nus->rx_handles.value_handle)
{
    // Set Protocol Mode characteristic value to default value
    default_protocol_mode = 0;

    // Initialize value struct.
    memset(&gatts_value, 0, sizeof(gatts_value));

    gatts_value.len     = sizeof(uint8_t);
    gatts_value.offset  = 0;
    gatts_value.p_value = &default_protocol_mode;

    err_code = sd_ble_gatts_value_set(lsp_nus->conn_handle,
    		lsp_nus->rx_handles.value_handle, &gatts_value);

The following link: devzone.nordicsemi.com/.../

claims that sd_ble_gatts_value_set() might not serve the purpose. Any thing else that I can try to make this work?

[Jørgen Holmefjord]

That link only say that you cannot write the cccd of the characteristics using sd_ble_gatts_value_set(). You should still be able to set the value of the characteristics using this function. I tested this on the BLE UART example, and that works fine. Are you getting any error codes from sd_ble_gatts_value_set() when you use that code? Note that you explicitly have to read the characteristics on the phone to get the value, you will not get any hints that a new value is available.

[Gauti]

Yes true, I used sd_ble_gatts_value_set() to set the value directly as you mentioned. I did not get any error code, meaning return from this function was 0. I did try to explicitly read from the phone to fetch the value, but this was not successful. However I used another method. I manually enabled notification by using the function sd_ble_gatts_sys_attr_set(). I calculated the CRC (CRC-CCIT - 0xFFFF) and updated the same using this function. With the updated system attributes, I used sd_ble_gatts_hvx() to write the values. This seems to be working fine. Of course I have to explicitly read the value from the mobile.

[Eugene0469]

Hello. I'd like to read the temperature values in my nordic thingy without enabling notifications. Is there a way one can use the function sd_ble_gatts_value_set() to do this?