BLE RSCS transmission interval

[MinervaAirbagSystems]

Hi there,

I am trying to set up a BLE communication between a central and a peripheral. For this I have succesfully used the nRF RSCS example from Nordic. But the problem is now that with this example the central gets notifications with just 1Hz. 

The peripheral is updating the values each 5ms. 

Why is the central just gets updated about each second? How can I achieve a higher frequency here?

P.S I am working with two customs boards. Each is using NRF52832 with S132.

Best regards, Patrick

[Kenneth]

Hi,

The throughput will depend on the conneciton interval, the size of the payloads and how frequently you are transmitting the notifications from the peripheral device. I notice you are likely working on the nRF5 SDK in this case, howevever for new development you should really consider the nRF Connect SDK, new features are only introduced on the nRF Connect SDK moving forward.

Both the nRF5 SDK and nRF Connect SDK should have throughput examples that can be used as reference on how to transmit data more frequently.

Kenneth

[MinervaAirbagSystems]

Hi Kenneth, 

thank you for your answer! I checked nRF Connect SDK, but I didn´t get the benefit. The biggest benefit I can see, is that I can use it with VS, which is really nice. But I don´t see how this help me with my problem?

Right now I am using an nRF throughput example (ble_app_rscs) and it is basically working fine. My only problem is that the central is just getting a notification every single second, but I am updating on the peripheral every 200ms.

I found this documentation (Running Speed and Cadence Service – Bluetooth® Technology Website). There they in "Running Speed And Cadence Service 1.0" on page 11 at point 3.1.1.6 Transmission Interval: "In typical applications, the RSC Measurement characteristic is notified approximately once per second. The Total Distance field, if supported, is typically included in the RSC Measurement characteristic for transmission approximately once every 2 or 3 seconds. These intervals may vary and are determined by the Server and are not required to be configurable by the Client."

And my question is now: Can I change this transmission interval?

Patrick

[Kenneth]

Hi,

The short answer to your question is that data is sent from the GATT server to the GATT client every time the sd_ble_gatts_hvx() api is called, so calling this more frequently will send it more frequently:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v7.3.0/group___b_l_e___g_a_t_t_s___h_v_n___m_s_c.html 

Kenneth

[MinervaAirbagSystems]

Oh I see. I am getting NRF_ERROR_RESSOURCES most of the time. I get NRF_SUCCESS just every full second. 

Where is handled how often central is checking for notifications? 

I mean the problem seems to be that peripheral is queuing too many notifications, when updating every 5ms. So is it possible to let the central check more often for notifications?

Patrick

[MinervaAirbagSystems]

I fixed it. I adjusted MIN_CONNECTION_INTERVAL and MAX_CONNECTION_INTERVAL. And now there is notification on central about every 10ms.

#define MIN_CONNECTION_INTERVAL         (uint16_t) MSEC_TO_UNITS(7.5, UNIT_1_25_MS)     /**< Determines minimum connection interval in milliseconds. */
#define MAX_CONNECTION_INTERVAL         (uint16_t) MSEC_TO_UNITS(10, UNIT_1_25_MS)      /**< Determines maximum connection interval in milliseconds. */
#define SLAVE_LATENCY                   0                                               /**< Determines slave latency in terms of connection events. */
#define SUPERVISION_TIMEOUT             (uint16_t) MSEC_TO_UNITS(4000, UNIT_10_MS)       /**< Determines supervision time-out in units of 10 milliseconds. */