/**
  * @ brief ADC sampling and SPI transmission on the Raspberry Pi Pico.
  * 
  * Reads an analogue voltage from ADC0, formats the raw value and computed voltage 
  * into a human-readable string, and transmits that string over SPI0 to a custom chip
  * once per second.
  * 
  * @author  Michael Gao
  * @date    2026
  * @license MIT
  */

#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "hardware/adc.h"
#include "hardware/spi.h"

// GPIO pin used for SPI chip select line.
#define PIN_CS 17

int main() {
  // Initialize stdio for serial console
  stdio_init_all();

  // ADC setup
  adc_init();
  adc_gpio_init(26);                          // Configure GPIO26 for ADC input
  adc_select_input(0);                     // Route ADC0 to result register
  printf("ADC0 initialized.\n");

  spi_init(spi0, 1000 * 1000);                         // 1 MHz clock
  gpio_set_function(18, GPIO_FUNC_SPI); // GPIO18 for SCK line
  gpio_set_function(19, GPIO_FUNC_SPI); // GPIO19 for SDI line
  gpio_init(PIN_CS);                                          // GPIO17 for nCS line
  gpio_set_dir(PIN_CS, GPIO_OUT);               // Drive chip select manually
  gpio_put(PIN_CS, 1);                                        // Deassert nCS

  while (true) {
    // Sample ADC and convert reading to voltage
    uint16_t raw = adc_read();
    float voltage = raw * (3.3f / 4095.0f);
    
    // Push ADC reading into a buffer
    char msg[64];
    snprintf(msg, sizeof(msg), "ADC Value: %u (%.2fV)\n", raw, voltage);

    // Transmit the ADC reading over SPI, manually setting the nCS line
    gpio_put(PIN_CS, 0);
    spi_write_blocking(spi0, (uint8_t *)msg, strlen(msg));
    gpio_put(PIN_CS, 1);

    // Debug
    printf("SPI sent: %s", msg);

    // Sample every 1 second
    sleep_ms(1000);
  }
}