DSP-ADAU1467/ModulosDSP_101.ino

// Modulos ADAU DSP WiFi + EEPROM (HTTP uploader + Sigma TCP bridge)
// Build: 260304_13  (YYMMDD_rev)
//
// This is a clean restore to the last known good state (v1.3.0/_04)
// with the chipAddr 0x01 fix applied. The receive loop is the original
// simple byte-at-a-time approach which correctly handled large packets.
//
// Changes vs original:
//  - sendReadResponse() corrected to 6-byte SigmaTCP header format
//  - sendWriteAck() added after every DSP/EEPROM write
//  - chipAddrTo7bit() handles 0x01=DSP, 0x02=EEPROM chip indexes
//  - I2C read failure returns zeros instead of dropping connection
//  - registerSize derived from ADAU1401 address map
//  - DSPWriter::resetSafeload() at start of each TCP session
//  - WS2812 NeoPixel on GPIO 21 (Waveshare ESP32-S3 Zero)
//
// Changelog v1.3.0:
//  - FIX: sendReadResponse() header corrected to 6-byte SigmaTCP format
//         (was 4 bytes; SigmaStudio expects: 0x0B, totalLen_hi, totalLen_lo, status, dataLen_hi, dataLen_lo)
//  - ADD: sendWriteAck() — SigmaStudio expects a 4-byte ACK after every write
//         (was missing; caused immediate disconnect after first write)
//  - FIX: I2C read failure now returns zeros instead of dropping TCP connection
//         (SigmaStudio can probe/read a DSP that isn't responding yet without aborting)
//  - ADD: Hex dump of first bytes of each received command to Serial for diagnostics
//  - ADD: printHex() debug helper
//
// Changelog v1.4.0:
//  - FIX: TCP receive loop replaced with client.readBytes() + 3s per-packet timeout
//         Previous byte-at-a-time loop timed out mid-transfer on large program blocks
//         (e.g. 1490-byte program download) because client.available() returns 0
//         between TCP segments even when more data is in flight. Now we block-read
//         exactly the bytes needed to complete the current packet, so a large program
//         download can span multiple TCP segments without triggering a false idle timeout.
//  - FIX: Idle timeout now only applies between commands, not during active receive
//
// Changelog v1.2.0:
//  - ADD: WS2812 NeoPixel status LED (Waveshare ESP32-S3 Zero, GPIO 21)
//         OFF        = idle / no TCP client
//         GREEN      = DSP write in progress
//         BLUE       = DSP read in progress
//         YELLOW     = EEPROM write via TCP
//         MAGENTA    = HTTP EEPROM upload in progress
//         RED flash  = error (I2C fail, overflow, bad packet)
//
// Changelog v1.1.0:
//  - FIX: Buffer overflow check moved to BEFORE write
//  - FIX: chipAddrTo7bit() replaced with explicit lookup table
//  - FIX: registerSize now derived from ADAU1401 address range
//  - FIX: DSPWriter::resetSafeload() called at TCP session start
//  - FIX: Safeload dataLen validated as multiple of 4
//  - FIX: totalLen vs dataLen cross-validated on WRITE packets

#include <WiFi.h>
#include <Wire.h>
#include <WebServer.h>
#include "DSPWriter.h"
#include <hd44780.h>
#include <hd44780ioClass/hd44780_I2Cexp.h>
#include <Adafruit_NeoPixel.h>
#include "FS.h"
#include <LittleFS.h>
#include <Update.h>
#include <ESPmDNS.h>

//=============================================================
// WiFi / UI
//=============================================================
const char* ssid     = "alfred";
const char* password = "alfred16";
const char* hostname = "modulos-dsp";
const char* version  = "VER: 260304_13";

#define I2C_SDA 13
#define I2C_SCL 12

WiFiServer tcpServer(8086);
WebServer  httpServer(80);

#include "index_html.h"
#include "ota_html.h"

hd44780_I2Cexp lcd;
static bool s_lcdOk = false;

//=============================================================
// NeoPixel status LED (Waveshare ESP32-S3 Zero, GPIO 21)
//=============================================================
#define NEOPIXEL_PIN    21
#define NEOPIXEL_COUNT  1
#define NEOPIXEL_BRIGHT 40

Adafruit_NeoPixel statusLed(NEOPIXEL_COUNT, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800);

static void ledSet(uint8_t r, uint8_t g, uint8_t b)
{
  statusLed.setPixelColor(0, statusLed.Color(r, g, b));
  statusLed.show();
}
static void ledOff()     { ledSet(0, 0, 0); }
static void ledCyan()    { ledSet(0, NEOPIXEL_BRIGHT/2, NEOPIXEL_BRIGHT/2); }
static void ledGreen()   { ledSet(0, NEOPIXEL_BRIGHT, 0); }
static void ledBlue()    { ledSet(0, 0, NEOPIXEL_BRIGHT); }
static void ledYellow()  { ledSet(NEOPIXEL_BRIGHT, NEOPIXEL_BRIGHT, 0); }
static void ledMagenta() { ledSet(NEOPIXEL_BRIGHT, 0, NEOPIXEL_BRIGHT); }
static void ledErrorFlash()
{
  for (int i = 0; i < 2; i++) {
    ledSet(NEOPIXEL_BRIGHT, 0, 0); delay(80);
    ledOff(); delay(80);
  }
}

//=============================================================
// TCP protocol buffer
//=============================================================
static uint8_t dataBuffer[50 * 1024];

#define STATE_START      0
#define STATE_READ_CMD   1
#define STATE_WRITE_CMD  2
#define CMD_WRITE 0x09
#define CMD_READ  0x0A

#define TCP_IDLE_TIMEOUT_MS 30000  // drop session if silent for 30 s

constexpr int WRITE_HDR_LEN = 10;
constexpr int READ_HDR_LEN  = 8;

struct adauWriteHeader {
  uint8_t  command;
  uint8_t  safeload;
  uint8_t  placement;
  uint16_t totalLen;
  uint8_t  chipAddr;
  uint16_t dataLen;
  uint16_t address;
};

struct adauReadHeader {
  uint8_t  command;
  uint16_t totalLen;
  uint8_t  chipAddr;
  uint16_t dataLen;
  uint16_t address;
};

static adauWriteHeader writeHeader;
static adauReadHeader  readHeader;

static constexpr uint8_t DSP_7BIT    = DSP_I2C_ADDRESS;    // 0x34
static constexpr uint8_t EEPROM_7BIT = EEPROM_I2C_ADDRESS; // 0x50

//=============================================================
// 24C256 EEPROM
//=============================================================
static constexpr uint32_t EEPROM_SIZE_BYTES   = 32768;
static constexpr uint16_t EEPROM_PAGE_SIZE    = 64;
static constexpr uint8_t  I2C_MAX_DATA_PER_TX = 28;

//=============================================================
// CRC32
//=============================================================
static uint32_t crc32_update(uint32_t crc, const uint8_t* data, size_t len)
{
  crc = ~crc;
  for (size_t i = 0; i < len; i++) {
    crc ^= data[i];
    for (int b = 0; b < 8; b++) {
      uint32_t mask = -(crc & 1u);
      crc = (crc >> 1) ^ (0xEDB88320u & mask);
    }
  }
  return ~crc;
}

//=============================================================
// Helpers
//=============================================================
static uint8_t chipAddrTo7bit(uint8_t chipAddr)
{
  switch (chipAddr) {
    case 0x01: return 0x34; // chip index 1 = DSP
    case 0x02: return 0x50; // chip index 2 = EEPROM
    case 0x68: return 0x34;
    case 0xA0: return 0x50;
    case 0x34: return 0x34;
    case 0x50: return 0x50;
    default:
      if (chipAddr > 0x7F) return (uint8_t)(chipAddr >> 1);
      return chipAddr;
  }
}

static uint8_t registerSizeForAddress(uint16_t address, uint16_t dataLen)
{
  if (address == dspRegister::CoreRegister) {
    if (dataLen == 2)  return CORE_REGISTER_R0_REGSIZE;
    if (dataLen == 24) return HARDWARE_CONF_REGSIZE;
    return CORE_REGISTER_R0_REGSIZE;
  }
  if (address >= DSP_PROG_RAM_START && address <= DSP_PROG_RAM_END) return PROGRAM_REGSIZE;
  if (address < DSP_PROG_RAM_START)  return PARAMETER_REGSIZE;
  return HARDWARE_CONF_REGSIZE;
}

static bool i2cAckPoll(uint8_t addr7, uint32_t timeoutMs = 80)
{
  uint32_t start = millis();
  while ((millis() - start) < timeoutMs) {
    Wire.beginTransmission(addr7);
    if (Wire.endTransmission() == 0) return true;
    delay(1);
  }
  return false;
}

static bool eepromWritePageChunk(uint16_t memAddr, const uint8_t* data, uint16_t len)
{
  Wire.beginTransmission(EEPROM_7BIT);
  Wire.write((uint8_t)(memAddr >> 8));
  Wire.write((uint8_t)(memAddr & 0xFF));
  for (uint16_t i = 0; i < len; i++) Wire.write(data[i]);
  if (Wire.endTransmission() != 0) return false;
  return i2cAckPoll(EEPROM_7BIT, 120);
}

static bool eepromWriteBlock(uint16_t memAddr, const uint8_t* data, uint16_t len)
{
  while (len) {
    uint16_t pageOff     = memAddr % EEPROM_PAGE_SIZE;
    uint16_t spaceInPage = EEPROM_PAGE_SIZE - pageOff;
    uint16_t chunk = len;
    if (chunk > spaceInPage)         chunk = spaceInPage;
    if (chunk > I2C_MAX_DATA_PER_TX) chunk = I2C_MAX_DATA_PER_TX;
    if (!eepromWritePageChunk(memAddr, data, chunk)) return false;
    memAddr += chunk; data += chunk; len -= chunk;
    delay(0);
  }
  return true;
}

static bool eepromReadBlock(uint16_t memAddr, uint8_t* out, uint16_t len)
{
  Wire.beginTransmission(EEPROM_7BIT);
  Wire.write((uint8_t)(memAddr >> 8));
  Wire.write((uint8_t)(memAddr & 0xFF));
  if (Wire.endTransmission(false) != 0) return false;
  uint16_t got = 0;
  while (got < len) {
    uint8_t ask = (len - got) > 32 ? 32 : (len - got);
    if (Wire.requestFrom((int)EEPROM_7BIT, (int)ask) != ask) return false;
    for (uint8_t i = 0; i < ask; i++) out[got++] = Wire.read();
  }
  return true;
}

static bool dspReadBlock(uint16_t memAddr, uint8_t* out, uint16_t len)
{
  Wire.beginTransmission(DSP_7BIT);
  Wire.write((uint8_t)(memAddr >> 8));
  Wire.write((uint8_t)(memAddr & 0xFF));
  if (Wire.endTransmission(false) != 0) return false;
  uint16_t got = 0;
  while (got < len) {
    uint8_t ask = (len - got) > 32 ? 32 : (len - got);
    if (Wire.requestFrom((int)DSP_7BIT, (int)ask) != ask) return false;
    for (uint8_t i = 0; i < ask; i++) out[got++] = Wire.read();
  }
  return true;
}

// SigmaTCP read response: 0x0B, totalLen_hi, totalLen_lo, status, dataLen_hi, dataLen_lo, [payload]
static bool sendReadResponse(WiFiClient& client, const uint8_t* data, uint16_t dataLen, bool ok)
{
  uint16_t totalLen = 6 + dataLen;
  uint8_t hdr[6];
  hdr[0] = 0x0B;
  hdr[1] = (uint8_t)(totalLen >> 8);
  hdr[2] = (uint8_t)(totalLen & 0xFF);
  hdr[3] = ok ? 0x00 : 0x01;
  hdr[4] = (uint8_t)(dataLen >> 8);
  hdr[5] = (uint8_t)(dataLen & 0xFF);
  if (client.write(hdr, sizeof(hdr)) != sizeof(hdr)) return false;
  if (dataLen > 0) {
    if (ok && data) {
      if (client.write(data, dataLen) != dataLen) return false;
    } else {
      // send zeros so SigmaStudio doesn't stall on a failed read
      static uint8_t zeros[256];
      uint16_t rem = dataLen;
      while (rem) {
        uint16_t chunk = rem > sizeof(zeros) ? sizeof(zeros) : rem;
        if (client.write(zeros, chunk) != chunk) return false;
        rem -= chunk;
      }
    }
  }
  return true;
}

// SigmaTCP write ack: 0x09, 0x00, 0x04, status
static bool sendWriteAck(WiFiClient& client, bool ok)
{
  uint8_t ack[4] = { 0x09, 0x00, 0x04, ok ? (uint8_t)0x00 : (uint8_t)0x01 };
  return client.write(ack, sizeof(ack)) == sizeof(ack);
}

static void printHex(const char* label, const uint8_t* buf, uint16_t len, uint16_t maxPrint = 24)
{
  Serial.print(label);
  uint16_t n = len < maxPrint ? len : maxPrint;
  for (uint16_t i = 0; i < n; i++) {
    if (buf[i] < 0x10) Serial.print("0");
    Serial.print(buf[i], HEX);
    Serial.print(" ");
  }
  if (len > maxPrint) Serial.print("...");
  Serial.println();
}

static void printWifiInfo()
{
  Serial.println();
  Serial.println("WiFi connected.");
  Serial.print("WiFi IP: ");       Serial.println(WiFi.localIP());
  Serial.printf("Hostname: http://%s.local/\n", hostname);
  Serial.print("MAC: ");           Serial.println(WiFi.macAddress());
  Serial.println("Modulos AudioDSP");
  Serial.println(version);
  if (s_lcdOk) {
    lcd.setCursor(4, 3);
    lcd.print(WiFi.localIP());
  }
}

//=============================================================
// HTTP EEPROM uploader state
//=============================================================
static volatile bool     uploadActive = false;
static volatile bool     uploadVerify = false;
static volatile bool     uploadFailed = false;
static volatile uint32_t uploadBytes  = 0;
static volatile uint32_t uploadCrc    = 0;

//=============================================================
// HTTP handlers
//=============================================================
static String contentTypeFor(const String& path) {
  if (path.endsWith(".html")) return "text/html";
  if (path.endsWith(".css"))  return "text/css";
  if (path.endsWith(".js"))   return "application/javascript";
  if (path.endsWith(".png"))  return "image/png";
  if (path.endsWith(".jpg") || path.endsWith(".jpeg")) return "image/jpeg";
  if (path.endsWith(".webp")) return "image/webp";
  if (path.endsWith(".svg"))  return "image/svg+xml";
  if (path.endsWith(".ico"))  return "image/x-icon";
  if (path.endsWith(".woff")) return "font/woff";
  if (path.endsWith(".woff2"))return "font/woff2";
  return "application/octet-stream";
}

static bool streamFromFS(String path) {
  if (!LittleFS.exists(path)) {
    if (path.startsWith("/")) {
      String alt = path.substring(1);
      if (LittleFS.exists(alt)) path = alt; else return false;
    } else {
      String alt = "/" + path;
      if (LittleFS.exists(alt)) path = alt; else return false;
    }
  }
  File f = LittleFS.open(path, "r");
  if (!f) return false;
  httpServer.streamFile(f, contentTypeFor(path));
  f.close();
  return true;
}

static void handleRoot() {
  String html = FPSTR(INDEX_HTML);
  html.replace("{{IP}}", WiFi.localIP().toString());
  httpServer.send(200, "text/html; charset=utf-8", html);
}

static void handleStatus() {
  String s;
  s += "uploadActive="; s += (uploadActive ? "1" : "0"); s += "\n";
  s += "uploadFailed="; s += (uploadFailed ? "1" : "0"); s += "\n";
  s += "uploadBytes=";  s += String((uint32_t)uploadBytes); s += "\n";
  s += "uploadCRC32=0x"; s += String((uint32_t)uploadCrc, HEX); s += "\n";
  httpServer.send(200, "text/plain", s);
}

static void handleUploadDone() {
  if (uploadFailed) {
    httpServer.send(500, "text/plain", "Upload failed.\nCheck Serial log.\n");
    return;
  }
  String msg = "OK\nBytes written: " + String((uint32_t)uploadBytes) +
               "\nCRC32: 0x" + String((uint32_t)uploadCrc, HEX) + "\n";
  httpServer.send(200, "text/plain", msg);
}

static void handleUploadStream() {
  HTTPUpload& up = httpServer.upload();

  if (up.status == UPLOAD_FILE_START) {
    uploadActive = true; uploadFailed = false; uploadBytes = 0; uploadCrc = 0;
    uploadVerify = httpServer.hasArg("verify");
    Serial.println(); Serial.print("HTTP upload start: "); Serial.println(up.filename);
    Serial.print("Verify: "); Serial.println(uploadVerify ? "yes" : "no");
    Wire.beginTransmission(EEPROM_7BIT);
    Serial.print("EEPROM probe err: "); Serial.println(Wire.endTransmission());
  }
  else if (up.status == UPLOAD_FILE_WRITE) {
    if (uploadFailed) return;
    if ((uploadBytes + up.currentSize) > EEPROM_SIZE_BYTES) {
      Serial.println("Upload too large for 24C256"); uploadFailed = true; return;
    }
    if (!eepromWriteBlock((uint16_t)uploadBytes, up.buf, (uint16_t)up.currentSize)) {
      Serial.println("EEPROM write failed"); uploadFailed = true; return;
    }
    uploadCrc = crc32_update(uploadCrc, up.buf, up.currentSize);
    uploadBytes += up.currentSize;
    ledMagenta();
  }
  else if (up.status == UPLOAD_FILE_END) {
    Serial.print("HTTP upload end, bytes="); Serial.println((uint32_t)uploadBytes);
    if (uploadVerify && !uploadFailed) {
      Serial.println("Verify start (CRC32)...");
      uint32_t crc = 0;
      static uint8_t tmp[256];
      uint32_t remaining = uploadBytes; uint16_t addr = 0;
      while (remaining) {
        uint16_t n = remaining > sizeof(tmp) ? sizeof(tmp) : (uint16_t)remaining;
        if (!eepromReadBlock(addr, tmp, n)) { Serial.println("EEPROM read failed"); uploadFailed = true; break; }
        crc = crc32_update(crc, tmp, n);
        addr += n; remaining -= n; delay(0);
      }
      Serial.print("Verify CRC32: 0x"); Serial.println(crc, HEX);
      if (!uploadFailed && crc != uploadCrc) { Serial.println("CRC mismatch"); uploadFailed = true; }
    }
    uploadActive = false; ledOff();
    Serial.println(uploadFailed ? "HTTP upload result: FAIL" : "HTTP upload result: OK");
  }
  else if (up.status == UPLOAD_FILE_ABORTED) {
    Serial.println("HTTP upload aborted"); uploadActive = false; uploadFailed = true; ledOff();
  }
}

//=============================================================
// HTTP DSP reset handler
//=============================================================
static void handleDspReset() {
  Serial.println("DSP soft reset requested");
  // Stop DSP execution, brief pause, restart. Program and parameter RAM
  // are preserved — this restarts execution without reloading from EEPROM.
  uint8_t stop[2]  = { 0x00, 0x00 };
  uint8_t run[2]   = { 0x00, 0x01 };
  DSPWriter::writeRegister(dspRegister::CoreRegister, sizeof(stop), stop);
  delay(100);
  DSPWriter::writeRegister(dspRegister::CoreRegister, sizeof(run),  run);
  Serial.println("DSP soft reset complete");
  httpServer.send(200, "text/plain", "DSP soft reset complete.");
}

//=============================================================
// HTTP OTA handlers
//=============================================================
static void handleOtaPage() {
  String html = FPSTR(OTA_HTML);
  html.replace("{{IP}}", WiFi.localIP().toString());
  httpServer.send(200, "text/html; charset=utf-8", html);
}

static void handleOtaDone() {
  if (Update.hasError()) {
    String err = "OTA failed: " + String(Update.errorString());
    Serial.println(err);
    httpServer.send(500, "text/plain", err);
  } else {
    httpServer.send(200, "text/plain", "Firmware updated — rebooting now.");
    Serial.println("OTA success — rebooting");
    delay(500);
    ESP.restart();
  }
}

static void handleOtaStream() {
  HTTPUpload& up = httpServer.upload();

  if (up.status == UPLOAD_FILE_START) {
    Serial.printf("OTA start: %s\n", up.filename.c_str());
    ledCyan();
    if (!Update.begin(UPDATE_SIZE_UNKNOWN)) {
      Serial.print("OTA begin failed: ");
      Update.printError(Serial);
    }
  }
  else if (up.status == UPLOAD_FILE_WRITE) {
    if (Update.write(up.buf, up.currentSize) != up.currentSize) {
      Serial.print("OTA write failed: ");
      Update.printError(Serial);
      ledErrorFlash();
    }
  }
  else if (up.status == UPLOAD_FILE_END) {
    if (Update.end(true)) {
      Serial.printf("OTA end: %u bytes written\n", up.totalSize);
    } else {
      Serial.print("OTA end failed: ");
      Update.printError(Serial);
      ledErrorFlash();
    }
    ledOff();
  }
  else if (up.status == UPLOAD_FILE_ABORTED) {
    Update.abort();
    Serial.println("OTA aborted");
    ledOff();
  }
}

//=============================================================
// Setup
//=============================================================
void setup() {
  Wire.begin(I2C_SDA, I2C_SCL);
  Wire.setClock(400000);

  statusLed.begin();
  statusLed.setBrightness(NEOPIXEL_BRIGHT);
  statusLed.show();

  s_lcdOk = (lcd.begin(20, 4) == 0);
  if (s_lcdOk) {
    lcd.display(); lcd.backlight();
    lcd.setCursor(2, 0); lcd.print("Modulos AudioDSP"); delay(1000);
    lcd.setCursor(5, 1); lcd.print("Booting..."); delay(1000);
  } else {
    Serial.println("LCD not found - continuing without display");
  }

  Serial.begin(115200); delay(1500);
  Serial.println(); Serial.println("Booting...");
  Serial.printf("Reset reason: %d\n", (int)esp_reset_reason());

  WiFi.mode(WIFI_STA);
  WiFi.setAutoReconnect(true);
  WiFi.begin(ssid, password);
  while (WiFi.waitForConnectResult() != WL_CONNECTED) {
    Serial.println("Connection Failed! Rebooting...");
    delay(5000); ESP.restart();
  }

  if (MDNS.begin(hostname)) {
    MDNS.addService("http", "tcp", 80);
    Serial.printf("mDNS: http://%s.local/\n", hostname);
  } else {
    Serial.println("mDNS start failed");
  }

  if (!LittleFS.begin(false)) {
    Serial.println("LittleFS mount failed, formatting...");
    if (!LittleFS.begin(true)) { Serial.println("LittleFS mount failed even after format"); return; }
  }
  Serial.println("LittleFS mounted OK");
  File root = LittleFS.open("/"); File f = root.openNextFile();
  while (f) { Serial.print("LittleFS: "); Serial.println(f.name()); f = root.openNextFile(); }

  if (s_lcdOk) { lcd.setCursor(3, 2); lcd.print("File System OK"); delay(1000); }

  tcpServer.begin();
  httpServer.on("/", HTTP_GET, handleRoot);
  httpServer.on("/status", HTTP_GET, handleStatus);
  httpServer.on("/upload", HTTP_POST, handleUploadDone, handleUploadStream);
  httpServer.on("/ota", HTTP_GET, handleOtaPage);
  httpServer.on("/ota_do", HTTP_POST, handleOtaDone, handleOtaStream);
  httpServer.on("/dsp_reset", HTTP_POST, handleDspReset);
  httpServer.onNotFound([]() {
    String uri = httpServer.uri();
    if (streamFromFS(uri)) return;
    Serial.print("HTTP 404: "); Serial.println(uri);
    httpServer.send(404, "text/plain", "Not found: " + uri);
  });
  httpServer.begin();

  if (s_lcdOk) {
    lcd.setCursor(4, 3); lcd.print("System Ready"); delay(1000);
    lcd.clear();
    lcd.setCursor(2, 0); lcd.print("Modulos AudioDSP");
    lcd.setCursor(3, 1); lcd.print(version); delay(500);
  }

  printWifiInfo();
  Serial.print("HTTP uploader: http://"); Serial.print(WiFi.localIP()); Serial.println("/");
}

//=============================================================
// TCP bridge
//=============================================================
//=============================================================
// TCP bridge
//=============================================================
static void handleTcpBridgeClient(WiFiClient& client)
{
  Serial.println("TCP new connection");
  DSPWriter::resetSafeload();

  int      writeIndex        = 0;          // next free slot in dataBuffer
  int      readIndex         = 0;          // start of current unprocessed command
  int      receivedByteCount = 0;          // total bytes written into dataBuffer
  int      currentState      = STATE_START;
  uint32_t lastActivityMs    = millis();   // idle watchdog

  while (client.connected()) {

    httpServer.handleClient();
    delay(0);

    // ------------------------------------------------------------------
    // STEP 1: Always drain the TCP stack into dataBuffer.
    // Do this unconditionally every loop iteration — this is what keeps
    // the TCP receive window open. If we only drain when we feel like it,
    // the window goes to zero and SigmaStudio stops sending (ZeroWindow).
    // ------------------------------------------------------------------
    while (client.available()) {
      if (writeIndex >= (int)sizeof(dataBuffer)) {
        Serial.println("TCP RX overflow");
        ledErrorFlash(); client.stop(); return;
      }
      int b = client.read();
      if (b < 0) break;
      dataBuffer[writeIndex++] = (uint8_t)b;
      receivedByteCount++;
      lastActivityMs = millis();
    }

    // ------------------------------------------------------------------
    // STEP 2: Process whatever is in the buffer.
    // This is driven purely by buffer contents, not by client.available().
    // We loop here processing commands until we run out of buffered data.
    // ------------------------------------------------------------------
    bool processedSomething = true;
    while (processedSomething && client.connected()) {
      processedSomething = false;

      // --- STATE_START: identify opcode ---
      if (currentState == STATE_START) {
        if (receivedByteCount <= readIndex) {
          // Buffer empty — reset for next command
          writeIndex = readIndex = receivedByteCount = 0;
          ledOff();
          break; // nothing to process, go back to receive loop
        }
        printHex("TCP RX: ", &dataBuffer[readIndex], (uint16_t)(receivedByteCount - readIndex));
        uint8_t op = dataBuffer[readIndex];
        if      (op == CMD_WRITE) { currentState = STATE_WRITE_CMD; processedSomething = true; }
        else if (op == CMD_READ)  { currentState = STATE_READ_CMD;  processedSomething = true; }
        else {
          Serial.printf("TCP invalid opcode: 0x%02X\n", op);
          ledErrorFlash();
          client.stop(); return;
        }
      }

      // --- STATE_WRITE_CMD ---
      if (currentState == STATE_WRITE_CMD) {
        // Need full header first
        if (receivedByteCount < (readIndex + WRITE_HDR_LEN)) break;

        writeHeader.safeload  = dataBuffer[readIndex + 1];
        writeHeader.placement = dataBuffer[readIndex + 2];
        writeHeader.totalLen  = (uint16_t)((dataBuffer[readIndex + 3] << 8) | dataBuffer[readIndex + 4]);
        writeHeader.chipAddr  = dataBuffer[readIndex + 5];
        writeHeader.dataLen   = (uint16_t)((dataBuffer[readIndex + 6] << 8) | dataBuffer[readIndex + 7]);
        writeHeader.address   = (uint16_t)((dataBuffer[readIndex + 8] << 8) | dataBuffer[readIndex + 9]);

        if (writeHeader.totalLen != WRITE_HDR_LEN + writeHeader.dataLen) {
          Serial.printf("TCP WRITE bad totalLen: got %u expected %u\n",
                        writeHeader.totalLen, WRITE_HDR_LEN + writeHeader.dataLen);
          ledErrorFlash(); client.stop(); return;
        }

        // Need full payload — if not here yet, break back to receive loop
        if (receivedByteCount < (readIndex + WRITE_HDR_LEN + (int)writeHeader.dataLen)) {
          Serial.printf("TCP WRITE buffering: have %d need %d bytes\n",
                        receivedByteCount - readIndex,
                        WRITE_HDR_LEN + (int)writeHeader.dataLen);
          break;
        }

        readIndex += WRITE_HDR_LEN;
        uint8_t target7 = chipAddrTo7bit(writeHeader.chipAddr);

        if (target7 == EEPROM_7BIT) {
          ledYellow();
          bool ok = eepromWriteBlock(writeHeader.address, &dataBuffer[readIndex], writeHeader.dataLen);
          readIndex += writeHeader.dataLen;
          sendWriteAck(client, ok);
          if (!ok) { Serial.println("TCP EEPROM write failed"); ledErrorFlash(); }
          else ledOff();
          currentState = STATE_START;
          processedSomething = true;
          continue;
        }

        if (target7 != DSP_7BIT) {
          Serial.printf("TCP unknown chipAddr: 0x%02X\n", writeHeader.chipAddr);
          ledErrorFlash(); client.stop(); return;
        }

        ledGreen();
        uint8_t  registerSize = registerSizeForAddress(writeHeader.address, writeHeader.dataLen);
        uint16_t regAddress   = writeHeader.address;
        Serial.printf("TCP WRITE addr=0x%04X len=%u regSz=%u safeload=%u\n",
                      writeHeader.address, writeHeader.dataLen, registerSize, writeHeader.safeload);

        bool writeOk = true;
        if (writeHeader.safeload == 1) {
          if (writeHeader.dataLen % 4 != 0) {
            Serial.printf("TCP safeload dataLen %u not multiple of 4\n", writeHeader.dataLen);
            ledErrorFlash(); client.stop(); return;
          }
          int writeCount = writeHeader.dataLen / 4;
          int slri = readIndex;
          DSPWriter dspWriter;
          while (writeCount > 0) {
            uint8_t da[5] = { 0x00, dataBuffer[slri], dataBuffer[slri+1],
                                     dataBuffer[slri+2], dataBuffer[slri+3] };
            dspWriter.safeload_writeRegister(regAddress, da, writeCount == 1);
            regAddress++; slri += 4; writeCount--; delay(0);
          }
        } else {
          writeOk = DSPWriter::writeRegisterBlock(regAddress, writeHeader.dataLen,
                                                  &dataBuffer[readIndex], registerSize);
          if (!writeOk) Serial.println("TCP DSP block write failed");
        }

        readIndex += writeHeader.dataLen;
        if (!writeOk) ledErrorFlash(); else ledOff();
        sendWriteAck(client, writeOk);
        currentState = STATE_START;
        processedSomething = true;
        continue;
      }

      // --- STATE_READ_CMD ---
      if (currentState == STATE_READ_CMD) {
        if (receivedByteCount < (readIndex + READ_HDR_LEN)) break;

        readHeader.totalLen = (uint16_t)((dataBuffer[readIndex + 1] << 8) | dataBuffer[readIndex + 2]);
        readHeader.chipAddr =  dataBuffer[readIndex + 3];
        readHeader.dataLen  = (uint16_t)((dataBuffer[readIndex + 4] << 8) | dataBuffer[readIndex + 5]);
        readHeader.address  = (uint16_t)((dataBuffer[readIndex + 6] << 8) | dataBuffer[readIndex + 7]);
        readIndex += READ_HDR_LEN;

        uint8_t target7 = chipAddrTo7bit(readHeader.chipAddr);
        Serial.printf("TCP READ chip=0x%02X addr=0x%04X len=%u\n",
                      readHeader.chipAddr, readHeader.address, readHeader.dataLen);

        if (readHeader.dataLen > 4096) { readHeader.dataLen = 4096; }

        static uint8_t readOut[4096];
        bool ok = false;
        ledBlue();

        if      (target7 == EEPROM_7BIT) ok = eepromReadBlock(readHeader.address, readOut, readHeader.dataLen);
        else if (target7 == DSP_7BIT)    ok = dspReadBlock   (readHeader.address, readOut, readHeader.dataLen);
        else {
          Serial.printf("TCP unknown chipAddr (READ): 0x%02X\n", readHeader.chipAddr);
        }

        if (!ok) Serial.println("TCP READ I2C failed - sending zeros");
        if (!sendReadResponse(client, ok ? readOut : nullptr, readHeader.dataLen, ok)) {
          Serial.println("TCP READ send failed"); ledErrorFlash(); client.stop(); return;
        }

        ledOff();
        currentState = STATE_START;
        processedSomething = true;
        continue;
      }
    } // end process loop

    // Idle path — no data waiting, no command in progress.
    if (currentState == STATE_START && receivedByteCount == readIndex) {
      if (!client.available()) {
        if (millis() - lastActivityMs > TCP_IDLE_TIMEOUT_MS) {
          Serial.println("TCP idle timeout — closing session");
          ledErrorFlash();
          break;
        }
        httpServer.handleClient();
        delay(10);
      }
    }

  } // end main while loop

  DSPWriter::resetSafeload();  // flush any mid-session safeload before disconnect
  client.stop();
  Serial.println("TCP disconnected");
  ledOff();
}

//=============================================================
// WiFi watchdog
//=============================================================
static uint32_t s_wifiLastCheck = 0;
static bool     s_wifiLost      = false;

static void maintainWifi()
{
  if (millis() - s_wifiLastCheck < 5000) return;
  s_wifiLastCheck = millis();

  if (WiFi.status() != WL_CONNECTED) {
    if (!s_wifiLost) {
      Serial.println("WiFi lost");
      if (s_lcdOk) { lcd.setCursor(0, 3); lcd.print("WiFi lost...        "); }
      s_wifiLost = true;
    }
    WiFi.reconnect();
  } else if (s_wifiLost) {
    Serial.print("WiFi reconnected, IP: "); Serial.println(WiFi.localIP());
    MDNS.begin(hostname);
    MDNS.addService("http", "tcp", 80);
    tcpServer.begin();   // re-register listening socket with recovered stack
    printWifiInfo();     // update LCD with current IP
    s_wifiLost = false;
  }
}

//=============================================================
// Loop
//=============================================================
void loop() {
  maintainWifi();
  httpServer.handleClient();
  if (uploadActive) { delay(1); return; }
  WiFiClient client = tcpServer.available();
  if (client) handleTcpBridgeClient(client);
  delay(1);
}