Si570 Driver
Si570 Arduino library supporting 1 Hz tuning. This code was originally intended for supporting local efforts to build the Minima transceiver designed by Farhan Akhtar. Existing implementations of this driver used floating point math on the arduino that resulted in the minimum frequency change being greater than 1 Hz.
This driver implements 1 Hz tuning using fixed point math in the calculations for setting the DCO and various register settings.
This is the updated version of this driver. My initial implementation that I published suffered from a bug that caused the DCO to be reset on every update when tuning down in frequency. While the frequency was set correctly, the bug was causing the DCO to restart on every frequency change producing an audible click in the receiver audio.
The error was two-fold. First, I failed to reserve sufficient bits for the 3500 ppm calculation. Secondarily, the Arduino absolute value implementation was giving me inconsistent results (probably my error, but I chose to remove the function to solve the problem) and it was just simpler to remove the function from my code.
Lastly, I modified the Si570 code to only calculate the 3500 ppm offset whenever the DCO centre frequency was changed rather than on every frequency change in order to gain a slight performance improvement.