If don't use 32.768k low frequency crystal, what will happen?

[liujirong888]

Dear ,

          I use nRF52833 to transfer audio,but I found that this audio will delay 130ms.

I didn't use 32.768K low frequency crystal, do you think this will affect delay time?

I modified below definition from 1 to 2 in sdk_config.h

#define NRFX_CLOCK_CONFIG_LF_SRC   2

#define CLOCK_CONFIG_LF_SRC   2

[Vidar Berg]

Hello,

The LF clock does not affect the latency. Probably what you should look at is the connection interval. You can use the Connection Parameters Negotiation module for requesting a shorter interval in your application.

Best regards,

Vidar

[liujirong888]

Dear Vidar,

                 I am trying to shorter interval in my application,but I found that 

the interval seems already minimum 7 ms. Because I saw that "Minimum Connection Interval [ms] <7-4000>"

You can check below information for your reference. what should I do ?

// <o> Minimum Connection Interval [ms] <7-4000>
// <i> Set the Minimum Connection Interval that is sent in the Connection Parameter Update request.
/**@brief Minimum Connection Interval [ms] <7-4000> */
#define CONFIG_MIN_CONN_INTERVAL_MS 7
#define CONFIG_MIN_CONN_INTERVAL ROUNDED_DIV(100u * CONFIG_MIN_CONN_INTERVAL_MS, 125)

// <o> Maximum Connection Interval [ms] <7-4000>
// <i> Set the Maximum Connection Interval that is sent in the Connection Parameter Update request.
/**@brief Maximum Connection Interval [ms] <7-4000> */
#define CONFIG_MAX_CONN_INTERVAL_MS 7
#define CONFIG_MAX_CONN_INTERVAL ROUNDED_DIV(100u * CONFIG_MAX_CONN_INTERVAL_MS, 125)

[Vidar Berg]

Hi,

The shortest interval supported by the Bluetooth specification is 7.5 ms. Although, it is technically possible to set it lower if you have control of both sides of the link and use this proprietary extension here https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/llpm/README.html, you will end up sacrificing throughput for better latency.

[liujirong888]

Dear Vidar,

             Does nRF5_SDK_17.0.2_d674dde support llpm? I saw this is latest nRF connect SDK?

My current software run in the nRF5_SDK_17.0.2_d674dde. so I should set it lower in both sides of the link?

[Vidar Berg]

Hi,

It's only supported in the Connect SDK. And as I indicated earlier, LLPM is not really suited for audio transfers as you will give you a reduced data rate.

If this is for continuous Audio streaming then you should consider LE Audio: https://www.nordicsemi.com/Products/Bluetooth-LE-Audio

[liujirong888]

Dear Vidar,

        I tried to modify the CONN_INTERVAL as below to 2ms,seem have little improvement.

But I need to improve from 130ms latency to 20ms latency. So only modify conn_interval can not fix this issue. 

#define CONFIG_MIN_CONN_INTERVAL_MS 2

//#define CONFIG_MIN_CONN_INTERVAL_MS 7

#define CONFIG_MAX_CONN_INTERVAL_MS 2

//#define CONFIG_MAX_CONN_INTERVAL_MS 7

//#define CONFIG_SLAVE_LATENCY 99

#define CONFIG_SLAVE_LATENCY 2

[Vidar Berg]

Hi,

The GAP central (phone, etc) will not accept a request for a connection interval lower than what is permitted by the specification (i.e. 7.5 ms).

I suggest you add the code below  to your BLE event handler to monitor the connection parameter updates and see what the connection interval actually ends up being.

/**@brief Function for handling BLE events.
 *
 * @param[in]   p_ble_evt   Bluetooth stack event.
 * @param[in]   p_context   Unused.
 */
static void ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context)
{
    uint32_t err_code;

    switch (p_ble_evt->header.evt_id)
    {  
        case BLE_GAP_EVT_CONN_PARAM_UPDATE:
        {
            /* Interval is given in units of 1.25 ms. Multiply by 1.25 to get interval in ms */
            uint32_t new_conn_interval =
                p_ble_evt->evt.gap_evt.params.conn_param_update.conn_params.max_conn_interval *
                1.25;

           NRF_LOG_INFO("Connection paramaters updated. New interval %d ms", new_conn_interval);
        }
        ...