current_sense/hardware_specific/rp2040/rp2040_mcu.h

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#pragma once
 
/*
 * RP2040 ADC features are very weak :-(
 *  - only 4 inputs
 *  - only 9 bit effective resolution
 *  - read only 1 input at a time
 *  - 2 microseconds conversion time!
 *  - no triggers from PWM / events, only DMA
 *
 * So to read 3 phases takes 6 microseconds. :-(
 * 
 * The RP2040 ADC engine takes over the control of the MCU's ADC. Parallel ADC access is not permitted, as this would
 * cause conflicts with the engine's DMA based access and cause crashes.
 * To use the other ADC channels, use them via this engine. Use addPin() to add them to the conversion, and getLastResult()
 * to retrieve their value at any time.
 * 
 * For motor current sensing, the engine supports inline sensing only.
 * 
 * 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
 * sensing to work correctly, all PWM slices have to be set to the same PWM frequency.
 * In theory, two motors could be sensed using 2 shunts on each motor.
 * 
 * Note that if using other ADC channels along with the motor current sensing, those channels will be subject to the same conversion schedule as the motor's ADC channels, i.e. convert at the same fixed rate in case
 * of inline sensing.
 * 
 * Solution to trigger ADC conversion from PWM via DMA:
 * use the PWM wrap as a DREQ to a DMA channel, and have the DMA channel write to the ADC's CS register to trigger an ADC sample.
 * Unfortunately, I could not get this to work, so no low side sensing for the moment.
 * 
 * Solution for ADC conversion:
 * ADC converts all channels in round-robin mode, and writes to FIFO. FIFO is emptied by a DMA which triggers after N conversions,
 * where N is the number of ADC channels used. So this DMA copies all the values from one round-robin conversion.
 * 
 * 
 */
 
 
#define SIMPLEFOC_RP2040_ADC_RESOLUTION 256
#ifndef SIMPLEFOC_RP2040_ADC_VDDA 
#define SIMPLEFOC_RP2040_ADC_VDDA 3.3f
#endif
 
 
union ADCResults {
    uint32_t value;
    uint8_t raw[4];
    struct {
        uint8_t ch0;
        uint8_t ch1;
        uint8_t ch2;
        uint8_t ch3;
    };
};
 
 
class RP2040ADCEngine {
 
public:
    RP2040ADCEngine();
    void addPin(int pin);
    //void setPWMTrigger(uint slice);
 
    bool init();
    void start();
    void stop();
 
    ADCResults getLastResults(); // TODO find a better API and representation for this
 
    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;
    bool initialized;
    uint readDMAChannel;
    //uint copyDMAChannel;
    //uint triggerDMAChannel;
 
    bool channelsEnabled[4];
    volatile uint8_t samples[4];
    volatile ADCResults lastResults;
    //alignas(32) volatile uint8_t nextResults[4];
};