Optimal ESP32 to AI-Thinker A7 Wiring & Pin Allocation

#include <Arduino.h>
#include <HardwareSerial.h>

// =================================================================
// OPTIMAL ZERO-CONFLICT PIN ALLOCATION FOR ESP32 & AI-THINKER A7
// =================================================================
// HardwareSerial 2: AT Command & Control
#define A7_AT_RX_PIN      35  // Input-Only (GPI) ← A7 U_TXD (Header P1 Pin 5)
#define A7_AT_TX_PIN      27  // Standard Output  → A7 U_RXD (Header P1 Pin 4)

// HardwareSerial 1: Dedicated GPS NMEA Stream
#define A7_GPS_RX_PIN     34  // Input-Only (GPI) ← A7 GPS_TXD (Header P1 Pin 11)
#define A7_GPS_TX_PIN     -1  // Unused (A7 GPS is receive-only on MCU)

// Power & Reset Management
#define PIN_A7_PWRKEY     32  // Standard Output  → A7 PWR_KEY (Header P2 Pin 11)
#define PIN_A7_RESET      33  // Optional Output  → A7 RESET (Header P2 Pin 5)

// Instantiate ESP32 Hardware UARTs
HardwareSerial A7_AT(2);   // UART 2
HardwareSerial A7_GPS(1);  // UART 1

// GPS Coordinates Cache
String g_lastNMEASentence = "";
bool g_gpsFixAcquired = false;

// Function Prototypes
void powerOnA7();
void processGPSStream();
void processCellularStream();

void setup() {
  // Console Monitor for Debugging (UART 0)
  Serial.begin(115200);
  while (!Serial && millis() < 2000);
  Serial.println(F("\n==========================================="));
  Serial.println(F("ESP32 & AI-Thinker A7 Zero-Conflict Boot"));
  Serial.println(F("==========================================="));

  // 1. Initialize HardwareSerial Interfaces using ESP32 GPIO Matrix
  // Serial2.begin(baud, config, rxPin, txPin);
  A7_AT.begin(115200, SERIAL_8N1, A7_AT_RX_PIN, A7_AT_TX_PIN);
  A7_GPS.begin(9600, SERIAL_8N1, A7_GPS_RX_PIN, A7_GPS_TX_PIN);

  Serial.println(F("[CONFIG] HardwareSerial 2 (AT) mapped: RX=35, TX=27"));
  Serial.println(F("[CONFIG] HardwareSerial 1 (GPS) mapped: RX=34"));

  // 2. Perform Active-HIGH Power-Up Routine
  powerOnA7();

  // 3. Configure Cellular Baseband
  Serial.println(F("[INIT] Testing AT communication..."));
  A7_AT.println("AT");
  delay(300);
  A7_AT.println("ATE0"); // Echo OFF
  delay(200);
  A7_AT.println("AT+CMGF=1"); // SMS Text Mode
  delay(200);
  A7_AT.println("AT+CNMI=2,2,0,0,0"); // Direct SMS output
  delay(200);

  // 4. Power On Internal GPS Core (Streams out of GPS_TXD / GPIO 34)
  Serial.println(F("[INIT] Enabling GPS positioning engine..."));
  A7_AT.println("AT+GPS=1");
  delay(300);

  Serial.println(F("[SYSTEM READY] Listening for GPS & Cellular events...\n"));
}

void loop() {
  // 1. Non-blocking handler for continuous 9600-baud GPS stream
  processGPSStream();

  // 2. Non-blocking handler for AT command replies & SMS notifications
  processCellularStream();

  // 3. User console passthrough (type AT commands directly in Serial Monitor)
  if (Serial.available()) {
    A7_AT.write(Serial.read());
  }
}

// Power On Sequence
void powerOnA7() {
  pinMode(PIN_A7_PWRKEY, OUTPUT);
  Serial.println(F("[BOOT] Pulsing PWR_KEY HIGH for 2.5 seconds..."));
  digitalWrite(PIN_A7_PWRKEY, HIGH);
  delay(2500);
  digitalWrite(PIN_A7_PWRKEY, LOW);
  Serial.println(F("[BOOT] PWR_KEY released. Waiting 4.5s for baseband startup..."));
  delay(4500);
}

// Parse Raw NMEA Stream from GPS_TXD (GPIO 34)
void processGPSStream() {
  static char gpsBuffer[128];
  static uint8_t gpsIdx = 0;

  while (A7_GPS.available()) {
    char c = A7_GPS.read();
    if (c == '\r') continue;
    if (c == '\n') {
      gpsBuffer[gpsIdx] = '\0';
      if (gpsIdx > 10) {
        // Inspect for RMC sentence ($GPRMC or $GNRMC)
        if (strstr(gpsBuffer, "$GPRMC") || strstr(gpsBuffer, "$GNRMC")) {
          g_lastNMEASentence = String(gpsBuffer);
          
          // Check Fix Status (Field 2: 'A' = Valid, 'V' = Warning/No Fix)
          char* statusPtr = strchr(gpsBuffer, ',');
          if (statusPtr) statusPtr = strchr(statusPtr + 1, ',');
          if (statusPtr && *(statusPtr + 1) == 'A') {
            if (!g_gpsFixAcquired) {
              Serial.println(F("\n>>> [GPS] 3D FIX ACQUIRED! <<<"));
              g_gpsFixAcquired = true;
            }
          }
        }
      }
      gpsIdx = 0;
    } else if (gpsIdx < sizeof(gpsBuffer) - 1) {
      gpsBuffer[gpsIdx++] = c;
    }
  }
}

// Forward AT events & SMS alerts to debug console
void processCellularStream() {
  while (A7_AT.available()) {
    char c = A7_AT.read();
    Serial.write(c);
  }
}

#include "driver/uart.h"
#include "driver/gpio.h"

#define A7_UART_NUM       UART_NUM_2
#define GPS_UART_NUM      UART_NUM_1

void init_a7_uart(void) {
    const uart_config_t uart_config = {
        .baud_rate = 115200,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };
    uart_param_config(A7_UART_NUM, &uart_config);
    
    // Assign Optimal Pins: TX = GPIO 27, RX = GPIO 35 (Input Only)
    uart_set_pin(A7_UART_NUM, GPIO_NUM_27, GPIO_NUM_35, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(A7_UART_NUM, 2048, 0, 0, NULL, 0);

    // GPS UART (9600 baud, RX only on GPIO 34)
    const uart_config_t gps_config = {
        .baud_rate = 9600,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };
    uart_param_config(GPS_UART_NUM, &gps_config);
    uart_set_pin(GPS_UART_NUM, UART_PIN_NO_CHANGE, GPIO_NUM_34, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(GPS_UART_NUM, 2048, 0, 0, NULL, 0);
}