• MCU module: U1 — SIWG917Y111MGABAR, Silicon Labs SiWG917 Wi-Fi 6 + BLE 5.4 module
• Recommended SDK: Silicon Labs WiSeConnect SDK / Simplicity Studio for SiWx917
• Programming/debug: J2 SWD plus UART ISP pins; SW2 pulls SWO_ISP low for ISP entry
• Sensor: U4 — SHT41-AD1B-R2 at I2C address 0x44

C
// app_pinmap.h — map these to the SDK GPIO/port macros for your selected SiWx917 board support package.
#pragma once

#define PIN_I2C_SDA_NET        "ULP_GPIO_0"   // schematic net I2C_SDA
#define PIN_I2C_SCL_NET        "ULP_GPIO_1"   // schematic net I2C_SCL
#define PIN_STATUS_LED_NET     "ULP_GPIO_8"   // schematic net STATUS_LED
#define PIN_EFUSE_FLT_N_NET    "UULP_VBAT_GPIO_3"
#define PIN_PWR_PGOOD_NET      "UULP_VBAT_GPIO_2"
#define SHT41_I2C_ADDR         0x44u
#define SENSOR_INTERVAL_MS     5000u

C
#include <stdint.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>

#include "sl_status.h"
#include "sl_sleeptimer.h"
#include "sl_wifi.h"
#include "sl_net.h"
#include "app_pinmap.h"

// Replace these three low-level functions with the SiWx917 SDK I2C/GPIO calls selected in the project configurator.
extern sl_status_t board_i2c_write(uint8_t addr, const uint8_t *data, uint16_t len);
extern sl_status_t board_i2c_read(uint8_t addr, uint8_t *data, uint16_t len);
extern void board_gpio_write_status_led(bool on);
extern bool board_gpio_read_efuse_fault_n(void);
extern bool board_gpio_read_pwr_pgood(void);
extern void board_platform_init(void);
extern uint32_t board_millis(void);

static uint8_t sht4x_crc8(const uint8_t *data, uint8_t len) {
  uint8_t crc = 0xFF;
  for (uint8_t i = 0; i < len; i++) {
    crc ^= data[i];
    for (uint8_t bit = 0; bit < 8; bit++) {
      crc = (crc & 0x80) ? (uint8_t)((crc << 1) ^ 0x31) : (uint8_t)(crc << 1);
    }
  }
  return crc;
}

static sl_status_t sht41_read(float *temp_c, float *rh_pct) {
  const uint8_t cmd = 0xFD; // high precision T/RH measurement
  uint8_t rx[6] = {0};
  sl_status_t st = board_i2c_write(SHT41_I2C_ADDR, &cmd, 1);
  if (st != SL_STATUS_OK) return st;

  sl_sleeptimer_delay_millisecond(10);
  st = board_i2c_read(SHT41_I2C_ADDR, rx, sizeof(rx));
  if (st != SL_STATUS_OK) return st;

  if (sht4x_crc8(&rx[0], 2) != rx[2] || sht4x_crc8(&rx[3], 2) != rx[5]) {
    return SL_STATUS_FAIL;
  }

  uint16_t t_ticks = ((uint16_t)rx[0] << 8) | rx[1];
  uint16_t rh_ticks = ((uint16_t)rx[3] << 8) | rx[4];
  *temp_c = -45.0f + 175.0f * ((float)t_ticks / 65535.0f);
  *rh_pct = -6.0f + 125.0f * ((float)rh_ticks / 65535.0f);
  if (*rh_pct > 100.0f) *rh_pct = 100.0f;
  if (*rh_pct < 0.0f) *rh_pct = 0.0f;
  return SL_STATUS_OK;
}

static void wifi_start_station(void) {
  // Start from a Silicon Labs SiWx917 Wi-Fi station example and fill credentials in the SDK config.
  // Keep this call non-fatal: the sensor node should still report over UART/debug if Wi-Fi is unavailable.
  sl_wifi_init(NULL, NULL, NULL);
}

void app_init(void) {
  board_platform_init();
  board_gpio_write_status_led(false);
  wifi_start_station();
  printf("SiWG917 T/RH sensor node starting\n");
}

void app_process_action(void) {
  static uint32_t last_ms = 0;
  uint32_t now = board_millis();
  if ((now - last_ms) < SENSOR_INTERVAL_MS) return;
  last_ms = now;

  bool power_good = board_gpio_read_pwr_pgood();
  bool efuse_ok = board_gpio_read_efuse_fault_n();
  if (!power_good || !efuse_ok) {
    printf("Power warning: PGOOD=%u EFUSE_FLT_N=%u\n", power_good, efuse_ok);
  }

  float temp_c = 0.0f, rh = 0.0f;
  sl_status_t st = sht41_read(&temp_c, &rh);
  if (st == SL_STATUS_OK) {
    board_gpio_write_status_led(true);
    printf("T=%.2f C RH=%.2f %%\n", temp_c, rh);
    // TODO: publish over Wi-Fi HTTP/MQTT or expose over BLE GATT characteristic.
    board_gpio_write_status_led(false);
  } else {
    printf("SHT41 read failed: 0x%08lx\n", (unsigned long)st);
  }
}

1. Create/import a Silicon Labs SiWx917 SoC Wi-Fi station example in Simplicity Studio.
2. Add the source above as app.c and implement the board-specific I2C/GPIO wrappers using the SDK configurator.
3. Build with Simplicity Studio or slc generate && make if using the command-line Silicon Labs flow.
4. Flash using SWD on J2: pin 1 = 3V3, pin 2 = SWDIO, pin 3/5/9 = GND, pin 4 = SWCLK, pin 10 = RESET_N.
5. To enter UART ISP mode, hold SW2 during reset and use J2 pin 7/8 for MCU UART RX/TX.