Need help

[NickAtGit]

Hey, great that you reverse engineered the Shimano bluetooth connection. I don't fully understand what you do here. Can you maybe explain more to me?

emtb/source/emtbDelegate.mc

Line 656 in 4667c43

mainView.values[9] = ((value[3] << 8) | value[2]).toFloat()/10;

Thanks

[markdotai]

Hi :) It looks like NicholasRasi decoded & added that bit, but what it looks to be doing is:

• The speed is stored using 2 bytes (in the array of bytes) and is a value in 100m/h.
• So first to combine the 2 bytes to a single integer value it multiplies the top byte by 256 (i.e. the <<8) and then it adds the bottom byte to that value (using the bitwise "or" operation). (Each byte stores an unsigned number from 0 to 255).
• It then converts the integer value to a floating point one so that it can be divided without losing precision, i.e. it will keep the fractional part after the division.
• It then divides by 10 to convert from 100m/h to km/h. I guess for Shimano showing the speed to the nearest km/h was not enough, and they wanted to give 1 decimal point of precision.

[NickAtGit]

Great, thanks for the explanation!