testing tutorial example ble custom service , the program stops on NRF_BREAKPOINT_COND and the console says

[jrt]

Hi, I take the tutorial here: https://github.com/NordicPlayground/nRF5x-custom-ble-service-tutorial

Because I have the SDK16 I made same mofification.

1) I comment all inside the static void sleep_mode_enter(void) function

2)  I comment :  err_code = bsp_btn_ble_init(NULL, &startup_event);    APP_ERROR_CHECK(err_code); in the buttons_leds_init function

3) I delete the btn config in the buttons_leds_init function , like that ---->  err_code = bsp_init(BSP_INIT_LEDS, bsp_event_handler); because I use the feather nrf52840, of course I have a custom_board.h file with the right LED.

With that, It  works with a timer sending notification each second. I don't try more than one minute.

Then I make some change, inthe main.c file :

#define MIN_CONN_INTERVAL               MSEC_TO_UNITS(10, UNIT_1_25_MS)        /**< Minimum acceptable connection interval (0.1 seconds). */
#define MAX_CONN_INTERVAL               MSEC_TO_UNITS(100, UNIT_1_25_MS) 

and

#define NOTIFICATION_INTERVAL           APP_TIMER_TICKS(50)     

In the ble_cus.c  in the ble_cus_custom_value_update function I had

 uint8_t cu[80];
    memset(cu, 0, sizeof(uint8_t));
    cu[0]=custom_value;

and you wil reconize these modified lines:

 gatts_value.len     = 80*sizeof(uint8_t);
    gatts_value.offset  = 0;
    gatts_value.p_value = cu;

of course I modified these lines too in the custom_value_char_add function

 attr_char_value.init_len  = 80*sizeof(uint8_t);
    attr_char_value.init_offs = 0;
    attr_char_value.max_len   = 80*sizeof(uint8_t);

You have guessed I want to increase the data rate.

I tryed the program , It runs during  some seconds and finishes with NRF_BREAKPOINT_COND and the console says <info> app: sd_ble_gatts_hvx result: 13. 

Have you an idea of my mistake ?

[jrt]

I progress in my research.

The bug does not happen every time, but often.

I catch the event BLE_GATTS_EVT_HVN_TX_COMPLETE, I can see that before the crash the sd_ble_gatts_hvx is called many time without any BLE_GATTS_EVT_HVN_TX_COMPLETE event . It seems that the softdevice has a buffer to memorise the packets to send, may be 4 or 5 packets maximum.

So I program my own buffer with 16 packets size. I call sd_ble_gatts_hvx only if I receive a BLE_GATTS_EVT_HVN_TX_COMPLETE event. And it works,,,, but the speed is low, I don't have a packet send each 50ms. So I presume that the softdevice loses speed if its buffer is empty,

So my second modification is: I call sd_ble_gatts_hvx if it miss less than 3 BLE_GATTS_EVT_HVN_TX_COMPLETE event to keep the softdevice buffer not empty, but not full too. And it works, An average of 50ms between each packet is respected.

I don't know if there is a configuration for the softdevice knowing that  I can see  my buffer has never more than 8 packets to memorise.