#include <Arduino.h>
#include <SPI.h>

#define DATA_LEN 16
#define DEFAULT_FREQ_MS 2UL
volatile uint8_t spiData[DATA_LEN]; volatile uint8_t spiIndex = 0;
volatile uint32_t spiIntervalMs = DEFAULT_FREQ_MS; volatile unsigned long spiCount = 0;     
volatile unsigned long lastSpiMicros = 0;

const uint8_t CMD_BUF_SIZE = 32; char cmdBuf[CMD_BUF_SIZE];
uint8_t cmdPos = 0; const int ledPin = 13;
unsigned long lastBlink = 0; bool ledState = LOW;

uint16_t msToOCR1A(uint32_t ms) {
  uint32_t ticks = (ms * 1000UL) / 4UL;
  if (ticks < 1) ticks = 1;
  if (ticks > 65535UL) ticks = 65535UL;
  return (uint16_t)(ticks - 1);
}

void setSpiIntervalMs(uint32_t ms) {
  if (ms < 1) ms = 1; cli();
  spiIntervalMs = ms;
  OCR1A = msToOCR1A(ms); sei();
}

void setupTimer1ForSpi(uint32_t ms) {
  noInterrupts();
  TCCR1A = 0; TCCR1B = 0;
  TCNT1  = 0; OCR1A = msToOCR1A(ms);
  TCCR1B |= (1 << WGM12); TCCR1B |= (1 << CS11) | (1 << CS10);
  TIMSK1 |= (1 << OCIE1A); interrupts();
}

ISR(TIMER1_COMPA_vect) {
  uint8_t b = spiData[spiIndex]; SPDR = b; spiIndex++;
  if (spiIndex >= DATA_LEN) spiIndex = 0; spiCount++; 
  lastSpiMicros = micros();
}

void parseCommand(const char *cmd) {
  while (*cmd == ' ' || *cmd == '\t') cmd++;
  if (strncmp(cmd, "SET FREQ", 8) == 0) {
    cmd += 8;
    while (*cmd == ' ' || *cmd == '\t') cmd++;
    int val = atoi(cmd);
    if (val == 2 || val == 5 || val == 10) {
      spiCount = 0; setSpiIntervalMs(val);
      Serial.print(F("OK: FREQ SET TO ")); Serial.print(val);
      Serial.println(F(" ms"));
      return;
    }
  }
  Serial.println(F("ERR: UNKNOWN CMD"));
}

void setup() {
  Serial.begin(115200);
  for (uint8_t i = 0; i < DATA_LEN; i++) spiData[i] = i; SPI.begin();
  pinMode(SS, OUTPUT); digitalWrite(SS, HIGH);
  setupTimer1ForSpi(spiIntervalMs); pinMode(ledPin, OUTPUT);
  Serial.println(F("READY. Commands: SET FREQ 2 / 5 / 10"));
}

void loop() {
  unsigned long m = millis();
  if (m - lastBlink >= 250) {
    lastBlink = m; ledState = !ledState;
    digitalWrite(ledPin, ledState);
  }

  while (Serial.available()) {
    char c = Serial.read();
    if (c == '\r') continue;
    if (c == '\n' || cmdPos >= CMD_BUF_SIZE - 1) {
      cmdBuf[cmdPos] = '\0';
      if (cmdPos > 0) parseCommand(cmdBuf);
      cmdPos = 0;
    } else {
      cmdBuf[cmdPos++] = c;
    }
  }

  static unsigned long lastStatus = 0;
  if (m - lastStatus >= 1000) {
    lastStatus = m; noInterrupts();
    uint32_t curInterval = spiIntervalMs; unsigned long count = spiCount;
    unsigned long lastMic = lastSpiMicros; interrupts();
    Serial.print(F("STATUS: interval="));
    Serial.print(curInterval);
    Serial.print(F(" ms, Count="));
    Serial.print(count);
    Serial.print(F(", lastSpiMicros="));
    Serial.println(lastMic);
  }
}