move default sample rate to header

Author: Richard Unger

src/current_sense/hardware_specific/rp2040/rp2040_mcu.cpp

@@ -164,7 +164,6 @@ bool RP2040ADCEngine::init() {
      false,             // We won't see the ERR bit because of 8 bit reads; disable.
      true               // Shift each sample to 8 bits when pushing to FIFO
     );
-    samples_per_second = 20000;
     if (samples_per_second<1 || samples_per_second>=500000) {
         samples_per_second = 0;
         adc_set_clkdiv(0);

src/current_sense/hardware_specific/rp2040/rp2040_mcu.h

@@ -22,6 +22,9 @@
  * Inline sensing is supported by offering a user-selectable fixed ADC sampling rate, which can be set between 500kHz and 1Hz.
  * After starting the engine it will continuously sample and provide new values at the configured rate.
  * 
+ * The default sampling rate is 20kHz, which is suitable for 2 channels assuming you a 5kHz main loop speed (a new measurement is used per
+ * main loop iteration).
+ * 
  * Low-side sensing is currently not supported.
  * 
  * The SimpleFOC PWM driver for RP2040 syncs all the slices, so the PWM trigger is applied to the first used slice. For current
@@ -74,7 +77,7 @@ class RP2040ADCEngine {
 
     ADCResults getLastResults(); // TODO find a better API and representation for this
 
-    int samples_per_second = 0; // leave at 0 to convert in tight loop
+    int samples_per_second = 20000; // 20kHz default (assuming 2 shunts and 5kHz loop speed), set to 0 to convert in tight loop
     float adc_conv = (SIMPLEFOC_RP2040_ADC_VDDA / SIMPLEFOC_RP2040_ADC_RESOLUTION); // conversion from raw ADC to float
 
     //int triggerPWMSlice = -1;