Application
For a more user-friendly setup experience of an iOS cycling app, I'd like to differentiate Garmin speed vs. cadence sensors prior to connection using only advertisement data.
Question
Does Garmin have a spec for the last two bytes of its advert manufacturer data?
Problem
The CBAdvertisementDataManufacturerDataKey yields:
let speed: [UInt8] = [135, 0, 12, 120] let cadence: [UInt8] = [135, 0, 13, 212]
The first byte (135) is Garmin's manufacturer identifier (0x0087). The second byte may be a reserved spacer. The third and fourth bytes are cryptic, not aligning to any operations I've conceived for the relevant values in either the Cycling Speed and Cadence Profile and Appearance Values documents. Is it uselessly variable (e.g., a serial number) or useful to parse?
Alternatively, I could parse device names, for "CAD" and "SPD", but I'd like something more reliable.
Notably, Apple does not provide Appearance advertisement data available on other platforms, which using an nRF sniffer does differentiate speed vs. cadence sensors prior to connection.