How to receive HCI events in a single thread with nrf connect SDK

[loquat]

I am planning to migrate from the nRF5 SDK to the nrf connect SDK.

My application is processing events from SoftDevice on a single thread.

In the same way, please tell me how to receive HCI events in a single thread with the nrf connect SDK.

[Vidar Berg]

Hi,

Multithread support is required for BLE, unfortunately. The reason for this is the Bluetooth host implementation relies on multiple threads to operate. 

Best regards,

Vidar

[loquat]

I will change the way the question is asked.

nrf connect SDK defines a number of BLE events (in other words, callback functions).

for example,
bt_le_scan_cb_t
bt_le_ext_adv_cb
bt_le_per_adv_sync_cb
bt_gatt_cb
bt_gatt_attr_read_func_t
bt_gatt_attr_write_func_t

I want to know how many threads are calling these.

I find it annoying to have to do lock processing every time I process a BLE event.

Most callbacks appear to be called from the System Workqueue.

[loquat]

When using SoftDevice Controller, hci_core.c/bt_recv_prio() is not called?(bt_recv() only?)

[Vidar Berg]

bt_recv_prio() is only to be used if you have selected this symbol here: https://github.com/nrfconnect/sdk-zephyr/blob/main/subsys/bluetooth/host/Kconfig#L97 

[loquat]

OK.

Are the following HighPriority events notified (callback) to the application?

(defined by hci_core.c / struct event_handler prio_events[])
BT_HCI_EVT_CMD_COMPLETE
BT_HCI_EVT_CMD_STATUS
BT_HCI_EVT_DATA_BUF_OVERFLOW
BT_HCI_EVT_DISCONN_COMPLETE
BT_HCI_EVT_NUM_COMPLETED_PACKETS

[Vidar Berg]

HCI is the communication interface between the Bluetooth controller and host, so it is the Bluetooth host API you should be looking at. 

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.2.0/zephyr/connectivity/bluetooth/api/index.html 

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.2.0/zephyr/connectivity/bluetooth/bluetooth-arch.html#id1 

[loquat]

yes. I understand It.

What I am concerned about is which thread (Context) is calling the callback when it is called back using the Bluetooth Host API.

I expect all callbacks to be called from SystemWorkq.

[Vidar Berg]

Was your question addressed by Amanda's reply in your other thread here:  Why is ble_rx_thread priority cooperative?  

[loquat]

No.

my question is

1. How all HCI events are called on SystemWrokq context (this thread)

2. How to set SystemWorkq priority to preemptive (other thread)

[Vidar Berg]

What thread/workqueue they are run in depends on your configuration settings here: https://github.com/nrfconnect/sdk-zephyr/blob/main/subsys/bluetooth/host/Kconfig#L97. You can open the thread viewer when debugging the application in VS code or Segger Ozone to confirm what thread a particular callback is run in. 

E.g.