Cumulative Crank Revs Explained

[Flemming Jensen]

Hi,

I am wondering about the Cumulative crank revs for service 0x1816 & 0x1818

Cycling Cadence and Speed, Cycling Power Services

I dont understand why the crank revs are to be sent out as cumulative values in a 16 bit field..

Does this mean that if you are doing 70 revs / minute you will have:

1 minute: 70 revs 2 minutes: 140 revs 3 minutes: 210 revs 936 minutes: 65520 937 minutes: ????55?

So there is a limit for fx spinning bikes about 15,6 hours?

Any input?

[RK]

The crank revolutions are sent out as cumulative vales in a 16 bit field because that's what the bluetooth spec as adopted by the Bluetooth SIG for the service mandates.

if you read the full spec, which can be downloaded here, it notes this value can roll over and documents that the collector shall take that into consideration, it also specifies an optional control point for setting it to a known value.

The spec doesn't have the working group's deliberations, so you can only guess why they did it that way, I would guess it was a tradeoff between utility and packet size.