Why does this particular flag involve an "or" operation?

RE: Why does this particular flag involve an "or" operation?

ovrebekk — Wed, 19 Oct 2016 06:45:59 GMT

Please accept one of the answers, to show the case as closed.

RE: Why does this particular flag involve an "or" operation?

Mitch996 — Wed, 19 Oct 2016 03:23:16 GMT

Got it. Much obliged.

RE: Why does this particular flag involve an "or" operation?

AmiguelS — Tue, 18 Oct 2016 09:18:19 GMT

The OR operator is being used to set multiple bits of that flag in a single line.

For example, conside you have a flag of 1 byte (8 bits), and each bit controls one feature.

#define FEATURE_ONE   0b00000001
#define FEATURE_TWO   0b00000010
#define FEATURE_THREE 0b00000100
#define FEATURE_FOUR  0b00001000
#define FEATURE_FIVE  0b00010000
#define FEATURE_SIX   0b00100000
#define FEATURE_SEVEN 0b01000000
#define FEATURE_EIGHT 0b10000000

And now you wish to turn on features 2 and 5. You can do so with

uint8_t flags = FEATURE_TWO | FEATURE_FIVE;

This works because when doing an OR of the two numbers, the set bits from each number prevail, so:

    00000010
    00010000
or__________
    00010010

RE: Why does this particular flag involve an "or" operation?

Mitch996 — Tue, 18 Oct 2016 06:51:00 GMT

I forgot to say that I was reading someone else's code. If it were me I wouldn't use the "|" operator like that. My question isn't with the protocol itself, but on the "|" operator, I've seen this use several times before but I didn't really care why or how until now.

RE: Why does this particular flag involve an "or" operation?

wlgrd — Tue, 18 Oct 2016 05:12:28 GMT

I don't really understand the question, and why you set your flags like this. If using the LE_ONLY flag you implicitly also set BLE_GAP_ADV_FLAG_BR_EDR_NOT_SUPPORTED.

#define BLE_GAP_ADV_FLAG_LE_GENERAL_DISC_MODE (0x02) Note that this define does not say LE_ONLY.

#define BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE (BLE_GAP_ADV_FLAG_LE_GENERAL_DISC_MODE | BLE_GAP_ADV_FLAG_BR_EDR_NOT_SUPPORTED)

Hence, if you want to set your flag like this, either change it to

uint8_t flags = BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE

uint8_t flags = BLE_GAP_ADV_FLAG_LE_GENERAL_DISC_MODE | BLE_GAP_ADV_FLAG_BR_EDR_NOT_SUPPORTED)