Dynamic allocate BLE observers

[nine-fox]

Hi

I am working on a firmware which can be used in serveral custom boards. While it works perfect in old sdk, I met the following problem when migrating from Sdk 12.2 to 14.2. Would you please take a look? Thanks

Since I HAVE serveral boards which will acts in different role, I need to add BLE observers dynamically. For example, one may acts as HID service and another acts NUS service. It works fine in sdk 12 because I can determine which service need to be initialised and which event handler will be added into evt_dispatch(). However, sdk14.2 is using static allocation, for example, BLE_HIDS_DEF. I can not control observers section. 

How can I dynamically allocate these observers?

[Håkon Alseth]

Hi,

 

Most of this is done in linker sections. This is what BLE_HIDS_DEF expands to:

#define BLE_HIDS_DEF(_name)                                                                         \
static ble_hids_t _name;                                                                            \
NRF_SDH_BLE_OBSERVER(_name ## _obs,                                                                 \
                     BLE_HIDS_BLE_OBSERVER_PRIO,                                                    \
                     ble_hids_on_ble_evt, &_name)

And NRF_SDH_BLE_OBSERVER(...) expands to defining a linker section (though several steps), which shall be declared in your linker script as the .sdh_ble_observer section:

*snip*
  .sdh_ble_observers :
  {
    PROVIDE(__start_sdh_ble_observers = .);
    KEEP(*(SORT(.sdh_ble_observers*)))
    PROVIDE(__stop_sdh_ble_observers = .);
  } > FLASH
*snip*

This tells the linker where the section is located both with a __start and a __stop symbol (think of it like a pointer), so that it is able to statically allocate 'n' amount of observers based on how many BLE_ANY_SERVICE_DEF(...) that you have in your application.

The library nrf_sdh will then iterate over all the BLE_*_DEF() objects so you do not have to go into your main.c::on_ble_evt() function to add another function call.

In order to migrate your current project to SDK 14.x, you need to conform to the BLE_*_DEF() API for your BLE observers, and updated your linker script. The linker script can be taken from almost any ble_app_* example, as they all include the sections needed. Remember that you might need to adjust the RAM start address.

Let me know if you run into trouble.

Cheers,

Håkon

[nine-fox]

Hi Håkon,

Thanks a lot for your detailed reply! Following your guide, I can define these observers successfully. However, it is *STATIC*.

For example, my firmware needs to start with HID and NUS service for DEVICE A, so I add the following lines in my code:

BLE_HIDS_DEF(m_hids);

BLE_NUS_DEF(m_nus);

However, when this firmware starts for DEVICE B, it only needs NUS service ONLY. As a result, m_hids is not used, and the hid listener is added anyway. 

How can I add NUS service and listen for NUS events only for DEVICE B? (while DEVICE A works well)

Thanks,

Vincent

[Håkon Alseth]

Hi Vincent,

Sorry for misunderstanding, and thanks for clarifying your use-case!

I am functions from SDK v14, application ble_app_hids_keyboard as an example here;

you can mimic the "older" use-case by declaring the m_hids variable as you did in SDK 12, and then call "ble_hids_on_ble_evt(p_ble_evt, NULL)" from main.c::ble_evt_handler() with an if-condition for dynamic handling. Note that you'll also need to comment out (or, wrap an if-condition around if dynamic handling of HIDS) hids_init() in main.c::services_init().

If DEVICE B never needs the hid-service, then I would just use #ifdef to remove it from the project when compiling for this specific device.

Best regards,

Håkon

[nine-fox]

Hi Håkon,

Thanks a lot for your reply!

Your suggestions look great to me and I will have a try :-)

Vincent