Acceleration and deceleration are off by factor of 2.

[willdickson]

The acceleration and deceleration as set via the setAcc and setDec appear to be off by a factor of two. This issue appears to be due an error in the conversion constant in the accCalc and decCalc functions found in SparkFunAutoDriverSupport.cpp. According the the L6470 manual the conversion constant should be given by (tick^2)/(2^-40) where tick = 250ns. This gives ((250e-9)**2)/(2^-40) = 0.068719476736 However, the constant in the AutoDriver library is 0.137438 which appears to be off by approximately a factor of two.

[kanta]

I also noticed this problem with the above issue and recalculated the conversion formula. As @willdickson said, the conversion constant for ACC and DEC should be 0.06871948.
Also, the constant for INT_SPD is 4 times smaller than the datasheet, and the constant for SPEED is slightly smaller.

So these constants need to be fixed, I think.

Register Name	Current value	Calculated value
ACC / DEC	0.137438	0.06871948
INT_SPD	4.1943	16.777216
SPEED	67.106	67.108864