Unable to allocate buffer for op 0x1b when notifying

[DennisDG]

Dear all,

I stubled upon the following issue when developing a BLE sensor product. 

When I try to bt_gatt_notify(); With only one characteristic, there is not an issue at all and it is working like it should. But when I subscribe to 2 or more characteristics.
it prints the error: 

[00:06:18.153,180] <wrn> bt_conn: Unable to allocate buffer within timeout
[00:06:18.153,199] <err> bt_att: Unable to allocate buffer for op 0x1b
[00:06:18.153,210] <wrn> bt_gatt: No buffer available to send notification

Could any body help me to unwind / explain this issue?

The context of this project is a as follows:

1. There is a LIS2DH mems accelerometer that is bieng polled every 60ms. Every 60ms each accelerometer channel (3 in total) is being bt_gatt_notify()'ed to the central. so 3 notifications for every separate channel, X,Y,Z. 

2. The main MCU is the 54L15 (DevKit).

3. The polling of the accelerometer is done (via triggers) at the Connection interval. In this way the central device can control the sampling frequency from 60ms up to 1000ms.

4. I modifyed the my_LBS.c example from the https://github.com/NordicDeveloperAcademy/bt-fund/tree/main/l4/l4_e1_sol/src

I have searched for hours and hours but no result.


I hope you can help me

Dennis

Here is my prj.conf:

# Logger module

CONFIG_LOG=y

# Button and LED library

CONFIG_DK_LIBRARY=y

# Bluetooth LE

CONFIG_BT=y

CONFIG_BT_PERIPHERAL=y

CONFIG_BT_DEVICE_NAME="Level"

# Increase stack size for the main thread and System Workqueue

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

CONFIG_MAIN_STACK_SIZE=2048

#Added to solve hanging on k_sleep();

CONFIG_NRF_GRTC_START_SYSCOUNTER=y

# For LIS2DH sensor

CONFIG_SPI=y

CONFIG_SENSOR=y

CONFIG_LIS2DH=y

CONFIG_LIS2DH_TRIGGER_NONE=n

CONFIG_LIS2DH_MEASURE_TEMPERATURE=y

#for floating point printing (disable when in production code this floating print is inefficient)

CONFIG_CBPRINTF_FP_SUPPORT=y

#for the Connection interval trigger

CONFIG_BT_CTLR_SDC_EVENT_TRIGGER=y

CONFIG_IRQ_OFFLOAD=n

CONFIG_ZERO_LATENCY_IRQS=y

[Vidar Berg]

Hello,

From which context are the bt_gatt_notify() calls made? If they are executed from the system workqueue, it may prevent notification packets from being dequeued as they are sent out. In that case, please try to send the data from another thread such as main() or create a dedicated sender thread like in the peripheral_uart sample.

Best regards,

Vidar

[DennisDG]

Hi Vidar,

Thank you for replying.
I hope I interpret your question correctly.

1. The bt-gatt_notify() is called from this custom function Accel_send_X_Axis_notify().
This function checks if notify is enabled. if false, the notify will not be send.

2. This Accel_send_X_Axis_notify() function is placed within a function named testRunner().
Also the Accel_send_Y_Axis_notify() AND Accel_send_Z_Axis_notify() are at this location.

3. This testRunner() function is declared within the main.c

4. In the main.c, testRunner() is attached to the Connection Interval callback. that can be from 60...1000ms.

Any more tips? However I will have a look in to the pheripheral_uart sample with youre solution in mind.

Best regards,

Dennis

[Vidar Berg]

Hi Dennis,

Thanks for the additional information.

DennisDG said:

4. In the main.c, testRunner() is attached to the Connection Interval callback. that can be from 60...1000ms.

Did you use the event_trigger sample as a reference when you configured this callback? The work_handler() function in this sample is executed in the system workqueue and should not contain any potentially blocking function calls. Either way,  please try running testRunner() from a separate thread.

Best regards,

Vidar

[DennisDG]

Hi Vidar,

Thank you for your quick response

Indeed I have used: https://github.com/nrfconnect/sdk-nrf/tree/main/samples/bluetooth/event_trigger

Now I first will put testRunner() in a different thread.

Best regards,

Dennis