How do you set the Device Information Service to use notify in the char_props?

[Josh]

Using Nordic SDK 17.1

We've enabled the DIS ble service on our nrf52840 based board and can read each characteristic from the service but it takes around 60 millisec for each read to finish (using a custom iOS swift app).

We need to reduce this time and wanted to see if enabling notify on the DIS characteristics would work, but are having trouble testing it.

This is part of our DIS init code:

// Initialize Device Information Service.
    memset(&dis_init, 0, sizeof(dis_init));

    ble_srv_ascii_to_utf8(&dis_init.manufact_name_str, (char *)DEVICE_NAME);
    ble_srv_ascii_to_utf8(&dis_init.model_num_str, (char *)MODEL_NAME);
    ble_srv_ascii_to_utf8(&dis_init.serial_num_str, (char *)blem_get_serial_number());
    ble_srv_ascii_to_utf8(&dis_init.hw_rev_str, (char *)sys_get_hardware_version_string());
    ble_srv_ascii_to_utf8(&dis_init.fw_rev_str, (char *)sys_get_firmware_version_string());
    dis_init.dis_char_rd_sec = SEC_OPEN;

    err_code = ble_dis_init(&dis_init);

Inside the ble_dis.c code I tried to modify the add_char to so that each characteristic had the notification flag set like this:

add_char_params.uuid            = uuid;
add_char_params.max_len         = char_len;
add_char_params.init_len        = char_len;
add_char_params.p_init_value    = p_char_value;
add_char_params.char_props.read = 1;
add_char_params.read_access     = rd_sec;
//here
add_char_params.char_props.notify = 1;

But this didn't work.

What should I do?

[Vidar Berg]

Hello,

The simplest way to decrease response time is for the peripheral to request a shorter connection interval from the phone. iOS will accept a connection interval of 15 ms if both the maximum and minimum requests are set to 15 ms.

https://developer.apple.com/accessories/Accessory-Design-Guidelines.pdf 

Inside the ble_dis.c code I tried to modify the add_char to so that each characteristic had the notification flag set like this:

You must also set the .cccd_write_access member to 'SEC_OPEN'. But please note that the DIS profile does not support the notify property: https://www.bluetooth.com/specifications/specs/device-information-service-1-1/ 

Best regards,

Vidar

[Josh]

Thank you Vidar,

So, we updated the connection interval as you suggested but it didn't help.

Since the DIS service doesn't support notify I suppose there is no way for the nrf52840 to send up the DIS characterstics unless the mobile BLE clients requests it with a read (using indicate), correct?

[Vidar Berg]

I'm surprised the shorter connection interval didn't help. Maybe the read request overlap with other procedures such as service discovery. A sniffer capture (nRF Sniffer for Bluetooth LE) would tell us more.

Do you plan to read the DIS characteristics once per connection?

Josh said:

Since the DIS service doesn't support notify I suppose there is no way for the nrf52840 to send up the DIS characterstics unless the mobile BLE clients requests it with a read (using indicate), correct?

Yes, the client must send a read request (this is not the same as an indication which is similar to notifications)

[Josh]

Hi, there could have been an issue with the connection interval setting. We are going to try again and get back to you. Thanks!