• MCU: EFR32MG22C224F512IM32-CR
• Framework: Silicon Labs Gecko SDK / Simplicity Studio
• Build system: Simplicity Studio project using EFR32MG22 target board support, or a custom Gecko SDK C project
• Primary purpose: bring up power/debug, read harvested reservoir voltage, generate PDM microphone clock/data capture hooks, and expose a location for radio burst code.

1. Power J1 with 5 V current-limited bench supply.
2. Verify 3V3 rail before attaching debugger.
3. Attach SWD debugger to J2: 3V3, GND, SWDIO, SWCLK, RESET_N.
4. Confirm HFXO starts with the selected 38.4 MHz crystal before enabling BLE/Zigbee radio.
5. Confirm HARV_SENSE never exceeds the ADC input range. With R3 = 1 MΩ and R4 = 330 kΩ, HARV_SENSE = VHARV * 0.248.

C
#include "em_device.h"
#include "em_chip.h"
#include "em_cmu.h"
#include "em_gpio.h"
#include "em_iadc.h"
#include "em_timer.h"
#include <stdint.h>
#include <stdbool.h>

// Pin mapping from schematic
#define PDM_CLK_PORT       gpioPortC
#define PDM_CLK_PIN        0
#define PDM_DATA_PORT      gpioPortC
#define PDM_DATA_PIN       1
#define HARV_ADC_PORT      gpioPortA
#define HARV_ADC_PIN       3

// Harvest divider: R3 = 1M, R4 = 330k
#define HARV_DIVIDER_RATIO (330000.0f / (1000000.0f + 330000.0f))
#define IADC_VREF_MV       1210.0f
#define IADC_MAX_COUNTS    4095.0f

static volatile uint32_t g_pdm_edge_count = 0;

static void initClocks(void)
{
  CMU_ClockEnable(cmuClock_GPIO, true);
  CMU_ClockEnable(cmuClock_IADC0, true);
  CMU_ClockEnable(cmuClock_TIMER0, true);
}

static void initGpio(void)
{
  // PDM clock output. TIMER0 route can be added after selecting final clock rate.
  GPIO_PinModeSet(PDM_CLK_PORT, PDM_CLK_PIN, gpioModePushPull, 0);

  // PDM data input from microphone.
  GPIO_PinModeSet(PDM_DATA_PORT, PDM_DATA_PIN, gpioModeInputPull, 0);

  // Harvest sense analog input.
  GPIO_PinModeSet(HARV_ADC_PORT, HARV_ADC_PIN, gpioModeDisabled, 0);
}

static void initHarvestAdc(void)
{
  IADC_Init_t init = IADC_INIT_DEFAULT;
  IADC_AllConfigs_t allConfigs = IADC_ALLCONFIGS_DEFAULT;
  IADC_InitSingle_t initSingle = IADC_INITSINGLE_DEFAULT;
  IADC_SingleInput_t singleInput = IADC_SINGLEINPUT_DEFAULT;

  // Use internal reference; tune prescalers in production project using Clock Manager.
  allConfigs.configs[0].reference = iadcCfgReferenceInt1V2;
  allConfigs.configs[0].vRef = 1210;
  allConfigs.configs[0].analogGain = iadcCfgAnalogGain1x;

  // Port A pin 3 maps to iadcPosInputPortAPin3 on Series 2 devices.
  singleInput.posInput = iadcPosInputPortAPin3;
  singleInput.negInput = iadcNegInputGnd;

  IADC_init(IADC0, &init, &allConfigs);
  IADC_initSingle(IADC0, &initSingle, &singleInput);
}

static uint32_t readHarvestAdcCounts(void)
{
  IADC_command(IADC0, iadcCmdStartSingle);
  while ((IADC0->STATUS & IADC_STATUS_SINGLEFIFODV) == 0) {
    // Wait for conversion complete.
  }
  IADC_Result_t result = IADC_pullSingleFifoResult(IADC0);
  return result.data;
}

static float readHarvestVoltage(void)
{
  uint32_t counts = readHarvestAdcCounts();
  float sense_mv = ((float)counts / IADC_MAX_COUNTS) * IADC_VREF_MV;
  float vharv_mv = sense_mv / HARV_DIVIDER_RATIO;
  return vharv_mv / 1000.0f;
}

static void initPdmClockTimer(void)
{
  // This creates a simple firmware-visible PDM clock pin state for bring-up.
  // For production audio capture, replace this with the EFR32 PDM peripheral or
  // a TIMER/PRS route that generates the required 1.0 MHz to 4.8 MHz PDM clock.
  TIMER_Init_TypeDef timerInit = TIMER_INIT_DEFAULT;
  timerInit.enable = true;
  timerInit.prescale = timerPrescale1;
  TIMER_Init(TIMER0, &timerInit);
}

static void pdmBringupTick(void)
{
  // Lightweight pin activity counter to prove the microphone DATA line is alive
  // while the final PDM peripheral/DMA capture path is being implemented.
  static uint8_t last = 0;
  uint8_t now = GPIO_PinInGet(PDM_DATA_PORT, PDM_DATA_PIN);
  if (now != last) {
    g_pdm_edge_count++;
    last = now;
  }
}

void app_init(void)
{
  CHIP_Init();
  initClocks();
  initGpio();
  initHarvestAdc();
  initPdmClockTimer();
}

void app_process_action(void)
{
  static uint32_t loop_count = 0;

  pdmBringupTick();

  if ((loop_count++ % 10000u) == 0u) {
    float vharv = readHarvestVoltage();
    (void)vharv;
    // Add logging through RTT/SWO/USART if enabled in the project.
    // Add radio burst trigger here once the selected Silicon Labs stack is configured.
  }
}

• Replace the PDM bring-up counter with the EFR32 PDM peripheral plus DMA buffer capture.
• Add packet framing and radio transmit using the chosen Silicon Labs stack: Bluetooth LE, Zigbee, or proprietary RAIL.
• Add a charge-and-fire policy: only sample/transmit when VHARV exceeds a configurable threshold.
• Add calibration for the R3/R4 divider and ADC reference.