#include <SPI.h>

// SPI pins - A0 board, BUS1 (J1 header)
#define PIN_SPI_SCK  20  // J1 pin 4
#define PIN_SPI_MISO 19  // J1 pin 5
#define PIN_SPI_MOSI 18  // J1 pin 6
#define CS_PIN        2  // J1 pin 3 (S2LP CSN)
#define SDN_PIN       1  // J1 pin 2 (S2LP SDN - shutdown/enable)

// S2-LP SPI header bytes
#define S2LP_WRITE  0x00
#define S2LP_READ   0x01
#define S2LP_STROBE 0x80

// S2-LP command strobes
#define CMD_SRES 0x70  // Reset

// S2-LP register map (device identification + state)
#define REG_DEVICE_INFO1 0xF0  // PARTNUM, expect 0x03
#define REG_DEVICE_INFO0 0xF1  // VERSION
#define REG_MC_STATE0    0xC0  // state machine status

SPIClass *s2lpSpi = NULL;

void s2lpWriteReg(uint8_t addr, uint8_t value) {
  digitalWrite(CS_PIN, LOW);
  s2lpSpi->transfer(S2LP_WRITE);
  s2lpSpi->transfer(addr);
  s2lpSpi->transfer(value);
  digitalWrite(CS_PIN, HIGH);
}

uint8_t s2lpReadReg(uint8_t addr) {
  digitalWrite(CS_PIN, LOW);
  s2lpSpi->transfer(S2LP_READ);
  s2lpSpi->transfer(addr);
  uint8_t value = s2lpSpi->transfer(0x00);
  digitalWrite(CS_PIN, HIGH);
  return value;
}

void s2lpStrobe(uint8_t cmd) {
  digitalWrite(CS_PIN, LOW);
  s2lpSpi->transfer(S2LP_STROBE);
  s2lpSpi->transfer(cmd);
  digitalWrite(CS_PIN, HIGH);
}

void setup() {
  Serial.begin(115200);
  delay(1000);

  Serial.println("=== RC-S2LP (868 MHz wM-Bus) Test - A0 BUS1 ===");

  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH);

  // Bring the chip out of shutdown: SDN high = shutdown, SDN low = active.
  // Pulse high first to guarantee a clean reset from an unknown state.
  pinMode(SDN_PIN, OUTPUT);
  digitalWrite(SDN_PIN, HIGH);
  delay(10);
  digitalWrite(SDN_PIN, LOW);
  delay(50); // allow POR / crystal settle before talking over SPI

  s2lpSpi = new SPIClass(FSPI);
  s2lpSpi->begin(PIN_SPI_SCK, PIN_SPI_MISO, PIN_SPI_MOSI, CS_PIN);
  s2lpSpi->setFrequency(1000000);
  s2lpSpi->setDataMode(SPI_MODE0);

  Serial.println("Sending SRES (software reset)...");
  s2lpStrobe(CMD_SRES);
  delay(100);

  uint8_t partnum = s2lpReadReg(REG_DEVICE_INFO1);
  uint8_t version = s2lpReadReg(REG_DEVICE_INFO0);
  uint8_t state   = s2lpReadReg(REG_MC_STATE0);

  Serial.print("PARTNUM  (0xF0): 0x"); Serial.println(partnum, HEX);
  Serial.print("VERSION  (0xF1): 0x"); Serial.println(version, HEX);
  Serial.print("MC_STATE (0xC0): 0x"); Serial.println(state, HEX);

  if (partnum == 0x03) {
    Serial.println("RESULT: PARTNUM matches S2-LP (0x03) - SPI link is good.");
  } else if (partnum == 0x00 || partnum == 0xFF) {
    Serial.println("RESULT: No response (0x00/0xFF). Check CS/SDN wiring.");
  } else {
    Serial.println("RESULT: Unexpected PARTNUM - double check register");
    Serial.println("        addresses against the S2-LP datasheet.");
  }
}

void loop() {
  uint8_t state = s2lpReadReg(REG_MC_STATE0);
  Serial.print("MC_STATE: 0x");
  Serial.println(state, HEX);
  delay(2000);
}

=== RC-S2LP (868 MHz wM-Bus) Test - A0 BUS1 ===
Sending SRES (software reset)...
PARTNUM  (0xF0): 0x3
VERSION  (0xF1): 0xC1
MC_STATE (0xC0): 0x0
RESULT: PARTNUM matches S2-LP (0x03) - SPI link is good.
MC_STATE: 0x0
MC_STATE: 0x0