Experiment in building a EuroPi script using the Pico C/C++ SDK (https://imgur.com/a/jjSMy6P)

clock_test.c

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include "pico/stdlib.h"
#include "pico/time.h"
#include "hardware/adc.h"
#include "hardware/gpio.h"
#include "hardware/i2c.h"
#include "hardware/pwm.h"

#include "ssd1306.h"

// App constants
#define N_SAMPLES 1000
uint16_t sample_buf[N_SAMPLES];

#define K1_GPIO 27
#define K2_GPIO 28
#define CV1_GPIO 21

#define MIN_BPM 20
#define MAX_BPM 240
#define TRIGGER_DURATION 15
#define CORRECTION_OFFSET 2
#define PPQN 4
#define MINUTE 60000 // in milliseconds

// Helpers

float toFloat(uint16_t val)
{
    return val;
}

// Init funcs

void setup_pwm(uint gpio)
{
    gpio_set_function(gpio, GPIO_FUNC_PWM);
    uint slice_num = pwm_gpio_to_slice_num(gpio);
    pwm_config config = pwm_get_default_config();
    pwm_init(slice_num, &config, true);
}

void setup_gpios(void)
{
    // OLED Display
    i2c_init(i2c0, 400000);
    gpio_set_function(0, GPIO_FUNC_I2C);
    gpio_set_function(1, GPIO_FUNC_I2C);
    gpio_pull_up(0);
    gpio_pull_up(1);

    // CV Outputs
    setup_pwm(CV1_GPIO);
}

void __not_in_flash_func(adc_capture)(uint16_t *buf, size_t count)
{
    adc_fifo_setup(true, false, 0, false, false);
    adc_run(true);
    for (int i = 0; i < count; i = i + 1)
        buf[i] = adc_fifo_get_blocking();
    adc_run(false);
    adc_fifo_drain();
}

uint16_t read_k(uint n)
{
    adc_select_input(n);
    adc_capture(sample_buf, N_SAMPLES);

    uint64_t sum = 0;
    for (int i = 0; i < N_SAMPLES; i++)
    {
        sum += sample_buf[i];
    }
    float avg = (float)sum / N_SAMPLES;
    return (1 << 12) - avg; // cast back to uin16
}

uint16_t read_bpm()
{
    float k1 = read_k(1) / toFloat(1 << 12);
    return ((MAX_BPM - MIN_BPM) * k1) + MIN_BPM;
}

uint16_t sleep_period(uint16_t bpm)
{
    return MINUTE / bpm / PPQN;
}

int main()
{
    // Init device
    stdio_init_all();
    setup_gpios();

    // Set up display
    ssd1306_t disp;
    disp.external_vcc = false;
    ssd1306_init(&disp, 128, 32, 0x3C, i2c0);
    ssd1306_clear(&disp);

    // Set up ADC
    adc_init();
    adc_gpio_init(K1_GPIO);
    adc_gpio_init(K2_GPIO);

    // Main app loop
    uint16_t bpm = 0;

    while (1)
    {
        uint16_t _bpm = read_bpm();
        if (_bpm != bpm)
        {
            bpm = _bpm;

            ssd1306_clear(&disp);

            char text[7];
            sprintf(text, "%d BPM", bpm);
            ssd1306_draw_string(&disp, 42, 8, 1, text);

            sprintf(text, "%d MS", sleep_period(bpm) * 4);
            ssd1306_draw_string(&disp, 42, 18, 1, text);

            ssd1306_show(&disp);
        }
        sleep_ms(sleep_period(bpm) - (TRIGGER_DURATION + CORRECTION_OFFSET));
        pwm_set_gpio_level(CV1_GPIO, (1 << 16) - 1);
        sleep_ms(TRIGGER_DURATION);
        pwm_set_gpio_level(CV1_GPIO, 0);
    }
}