setCodingRate logic incorrect

[rgillan]

Hi,
Great work on this, saved me a lot of time coding this up. Noticed that when setting the coding rate in the options it wasn't being set in the sx1276 correctly, so went digging. In the logic in SX127x.prototype.setCodingRate you are comparing the effective number set (4/5 or 0.8, 4/6 or 0.66 etc.). Your testing has the sequence backwards, and it will always result in 4/5 or denominator 5. The code should be

if (cr <= (4/8)) { denominator = 8; } else if (cr <= (4/7)) { denominator = 7; } else if (cr <= (4/6)) { denominator = 6; } else { denominator = 5; }
I've checked the register settings for all 4 coding rates and they are correct with the above changes.

[sandeepmistry]

Hi @rgillan, could you please submit a pull request for the suggested changes. Thanks.