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

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

liujirong888 — Thu, 07 Apr 2022 09:03:17 GMT

Dear Vidar,

Thank you for your reply. In fact,this audio software have 2 version, sender and receiver.

the sender and receiver both work on nRF52833 board.so this software don't need to connect to phone.

this software use proprietary 2.4G.I will check if can get the updated conn param.

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

Vidar Berg — Thu, 07 Apr 2022 08:50:32 GMT

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);
        }
        ...

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

liujirong888 — Thu, 07 Apr 2022 07:51:51 GMT

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

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

Vidar Berg — Thu, 07 Apr 2022 07:42:30 GMT

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

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

liujirong888 — Thu, 07 Apr 2022 06:50:19 GMT

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?

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

Vidar Berg — Wed, 06 Apr 2022 09:20:13 GMT

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.

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

liujirong888 — Wed, 06 Apr 2022 08:58:40 GMT

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)

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

Vidar Berg — Mon, 04 Apr 2022 06:59:31 GMT

Hello,

The Softdevice clock source is configured through the NRF_SDH_CLOCK_* symbols, and these are the recommended settings if you don't have a crystal:

// </h> 
//==========================================================

// <h> Clock - SoftDevice clock configuration

//==========================================================
// <o> NRF_SDH_CLOCK_LF_SRC  - SoftDevice clock source.
 
// <0=> NRF_CLOCK_LF_SRC_RC 
// <1=> NRF_CLOCK_LF_SRC_XTAL 
// <2=> NRF_CLOCK_LF_SRC_SYNTH 

#ifndef NRF_SDH_CLOCK_LF_SRC
#define NRF_SDH_CLOCK_LF_SRC 0
#endif

// <o> NRF_SDH_CLOCK_LF_RC_CTIV - SoftDevice calibration timer interval. 
#ifndef NRF_SDH_CLOCK_LF_RC_CTIV
#define NRF_SDH_CLOCK_LF_RC_CTIV 16
#endif

// <o> NRF_SDH_CLOCK_LF_RC_TEMP_CTIV - SoftDevice calibration timer interval under constant temperature. 
// <i> How often (in number of calibration intervals) the RC oscillator shall be calibrated
// <i>  if the temperature has not changed.

#ifndef NRF_SDH_CLOCK_LF_RC_TEMP_CTIV
#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 2
#endif

// <o> NRF_SDH_CLOCK_LF_ACCURACY  - External clock accuracy used in the LL to compute timing.
 
// <0=> NRF_CLOCK_LF_ACCURACY_250_PPM 
// <1=> NRF_CLOCK_LF_ACCURACY_500_PPM 
// <2=> NRF_CLOCK_LF_ACCURACY_150_PPM 
// <3=> NRF_CLOCK_LF_ACCURACY_100_PPM 
// <4=> NRF_CLOCK_LF_ACCURACY_75_PPM 
// <5=> NRF_CLOCK_LF_ACCURACY_50_PPM 
// <6=> NRF_CLOCK_LF_ACCURACY_30_PPM 
// <7=> NRF_CLOCK_LF_ACCURACY_20_PPM 
// <8=> NRF_CLOCK_LF_ACCURACY_10_PPM 
// <9=> NRF_CLOCK_LF_ACCURACY_5_PPM 
// <10=> NRF_CLOCK_LF_ACCURACY_2_PPM 
// <11=> NRF_CLOCK_LF_ACCURACY_1_PPM 

#ifndef NRF_SDH_CLOCK_LF_ACCURACY
#define NRF_SDH_CLOCK_LF_ACCURACY 1
#endif

The NRF_CLOCK_LF_SRC_SYNTH source is not low power, and is generally not recommended.

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

liujirong888 — Sat, 02 Apr 2022 02:21:00 GMT

Dear Vidar,

May I know how to set sdk_config.h if I don't want to use 32.768K crystal?

Does my current setting OK for not using 32.768K ?

#define NRFX_CLOCK_CONFIG_LF_SRC 2

#define CLOCK_CONFIG_LF_SRC 2

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

Vidar Berg — Fri, 01 Apr 2022 10:44:57 GMT

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