Question about SVCALL in ble_gap.h

[Michael]

I'm trying to follow the code from one of your examples, specifically ble_beacon in SDK 8.0 and eventually I get to a point where I'm not sure what's going on so I figured I'd ask a question about it. I have knowledge in object oriented programming but am still getting familiarized with BLE.

I started my trace from the "static void advertising_start(void)" function in main.c and was tracing "sd_ble_gap_adv_start" from the line: "err_code = sd_ble_gap_adv_start(&m_adv_params);"

this took me to the ble_gap.h header file where the function/service is mentioned twice:

enum BLE_GAP_SVCS { ..... SD_BLE_GAP_ADV_START, ..... };

and

SVCALL(SD_BLE_GAP_ADV_START, uint32_t, sd_ble_gap_adv_start(ble_gap_adv_params_t const *p_adv_params));

This is a specific example but in general I'm not sure what is going on in the codebase in circumstances such as this. Should there be a ble_gap.c file included in the project? Does this have something to do with the GAP from BLE? Is there something simple I'm missing?

[RK]

This is how the application communicates with the softdevice. The SVC calls (each of which has a different number) trigger the SVC IRQ handler which the softdevice implements and performs the requested action. This is why you don't have to link with the softdevice, there's nothing to link with, the entire communication between the two is done with SVC calls. That's also why there's no .c file, there's no C, apart from the SVCALL() macro which expands into 2 lines of assembler which call the SVC call with the correct number and return.

[Michael]

Thank you both for the explanation, that makes sense to hide the IP of the softdevice. Is all the available documentation about this provided in the html files of the SDK or is there somewhere else I can look for more information?