Basic working SD card.'

src/core/diagnostics_state.cpp

@@ -12,12 +12,6 @@ void DiagnosticsState::update()
 
     current.cpuFrequency =
         ESP.getCpuFreqMHz();    
-
-    Serial.print("#update: ");
-    Serial.println(current.freeHeap);
-    Serial.println("Calling current from update");
-    getCurrent();
-    
 }
 
 
@@ -29,9 +23,5 @@ DiagnosticSample DiagnosticsState::getCurrent()
     sample.freeHeap = current.freeHeap;
     sample.minimumFreeHeap = current.minimumFreeHeap;
     sample.cpuFrequency = current.cpuFrequency;
-
-    Serial.print("#getCurrent: ");
-    Serial.println(sample.freeHeap);
-    Serial.println(sample.timestamp);
     return sample;
 }

src/core/storage_state.cpp

@@ -0,0 +1,67 @@
+#include "storage_state.h"
+
+
+void StorageState::begin()
+{
+    current.mounted = false;
+    current.timestamp = 0;
+    current.totalMB = 0;
+    current.usedMB = 0;
+    current.freeMB = 0;
+    current.writeSpeedBps = 0;
+    current.cardType[0] = '\0';
+}
+
+
+void StorageState::setMounted(bool mounted)
+{
+    current.mounted = mounted;
+    current.timestamp = millis();
+}
+
+
+void StorageState::setCardType(const char* type)
+{
+    size_t i = 0;
+    for (i = 0; i < sizeof(current.cardType) - 1 && type[i] != '\0'; i++)
+    {
+        current.cardType[i] = type[i];
+    }
+    current.cardType[i] = '\0';
+}
+
+
+void StorageState::setCapacity(uint64_t totalBytes, uint64_t usedBytes)
+{
+    uint64_t freeBytes = (totalBytes > usedBytes) ? (totalBytes - usedBytes) : 0;
+
+    current.totalMB = (uint32_t)(totalBytes >> 20);
+    current.usedMB  = (uint32_t)(usedBytes >> 20);
+    current.freeMB  = (uint32_t)(freeBytes >> 20);
+}
+
+
+void StorageState::setWriteSpeedBps(uint32_t bytesPerSecond)
+{
+    current.writeSpeedBps = bytesPerSecond;
+}
+
+
+StorageSnapshot StorageState::getCurrent()
+{
+    StorageSnapshot snapshot;
+
+    snapshot.mounted = current.mounted;
+    snapshot.timestamp = current.timestamp;
+    snapshot.totalMB = current.totalMB;
+    snapshot.usedMB = current.usedMB;
+    snapshot.freeMB = current.freeMB;
+    snapshot.writeSpeedBps = current.writeSpeedBps;
+
+    for (size_t i = 0; i < sizeof(snapshot.cardType); i++)
+    {
+        snapshot.cardType[i] = current.cardType[i];
+    }
+
+    return snapshot;
+}

src/core/storage_state.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <Arduino.h>
+
+
+// Cross-task snapshot of the SD card, filled by the StorageTask (core 0) and
+// read by the WebService (core 1) for the dashboard broadcast. Values are
+// stored as 32-bit quantities (MB / Bps) so each field reads atomically.
+struct StorageSnapshot
+{
+    bool mounted;
+    uint32_t timestamp;
+    uint32_t totalMB;
+    uint32_t usedMB;
+    uint32_t freeMB;
+    uint32_t writeSpeedBps;
+    char cardType[16];
+};
+
+
+class StorageState
+{
+public:
+    void begin();
+
+    void setMounted(bool mounted);
+    void setCardType(const char* type);
+    void setCapacity(uint64_t totalBytes, uint64_t usedBytes);
+    void setWriteSpeedBps(uint32_t bytesPerSecond);
+
+    StorageSnapshot getCurrent();
+
+private:
+    volatile StorageSnapshot current;
+};

src/main.cpp

@@ -5,25 +5,30 @@
 
 #include "core/dashboard_state.h"
 #include "core/diagnostics_state.h"
+#include "core/storage_state.h"
 
 #include "services/service_manager.h"
 #include "services/wifi_service.h"
 #include "services/ota_service.h"
 #include "services/web_service.h"
 
+#include "storage/sd_manager.h"
+
 #include "tasks/system_task.h"
 #include "tasks/diagnostics_task.h"
+#include "tasks/storage_task.h"
 
 
 DashboardState dashboardState;
 DiagnosticsState diagnosticsState;
+StorageState storageState;
 
 // Simple service scheduler nice for grouping tasks
 ServiceManager services;
 
 WiFiService wifi;
 OTAService ota;
-WebService web(dashboardState, diagnosticsState);
+WebService web(dashboardState, diagnosticsState, storageState);
 
 
 // Actual FreeRTOS tasks that are scheduled
@@ -31,6 +36,9 @@ SystemTask systemTask(services);
 
 DiagnosticsTask diagnosticsTask(diagnosticsState);
 
+SDManager sdManager;
+StorageTask storageTask(sdManager, storageState);
+
 void setup()
 {
     Serial.begin(115200);
@@ -42,6 +50,7 @@ void setup()
 
     systemTask.start();
     diagnosticsTask.start();
+    storageTask.start();
 }
 
 

src/services/web_service.cpp

@@ -1,10 +1,11 @@
 #include "web_service.h"
 
-WebService::WebService(DashboardState& state, DiagnosticsState& diag_state)
+WebService::WebService(DashboardState& state, DiagnosticsState& diag_state, StorageState& storage_state)
     :
     Service("Web", 10),
     dashboardState(state),
     diagnosticsState(diag_state),
+    storageState(storage_state),
     server(80),
     webSocket(81)
 {
@@ -64,6 +65,11 @@ h1 {
   font-size: 28px;
   margin-top: 20px;
 }
+
+#sd_status {
+  font-size: 24px;
+  font-weight: bold;
+}
 </style>
 
 <script>
@@ -82,11 +88,13 @@ function connectWebSocket() {
     socket.onmessage = function(event) {
         const data = JSON.parse(event.data);
 
-        document.getElementById("uptime").innerHTML = data.system.uptime;
+        document.getElementById("uptime").innerHTML = "Uptime: " + data.system.uptime;
-        document.getElementById("firmware_version").innerHTML = data.system.version;
+        document.getElementById("firmware_version").innerHTML = "Firmware Version: " + data.system.version;
-        document.getElementById("free_heap").innerHTML = data.diagnostics.free_heap;
+        document.getElementById("free_heap").innerHTML = "Free Heap: " + data.diagnostics.free_heap;
-        document.getElementById("minimum_free_heap").innerHTML = data.diagnostics.minimum_free_heap;
+        document.getElementById("minimum_free_heap").innerHTML = "Minimum Free Heap: " + data.diagnostics.minimum_free_heap;
-        document.getElementById("cpu_frequency").innerHTML = data.diagnostics.cpu_frequency;
+        document.getElementById("cpu_frequency").innerHTML = "CPU Frequency: " + data.diagnostics.cpu_frequency + "MHz";
+
+        updateStorage(data.storage);
     };
 
     socket.onclose = function() {
@@ -95,6 +103,37 @@ function connectWebSocket() {
     };
 }
 
+function formatBytesMB(mb) {
+    const value = Number(mb);
+    if (value >= 1024) {
+        return (value / 1024).toFixed(2) + " GB";
+    }
+    return value.toFixed(0) + " MB";
+}
+
+function updateStorage(storage) {
+    const sdStatus = document.getElementById("sd_status");
+
+    if (storage && storage.mounted === "true") {
+        sdStatus.innerHTML = "SD card found";
+        sdStatus.style.color = "#00ff99";
+
+        document.getElementById("sd_type").innerHTML = "Card Type: " + storage.card_type;
+        document.getElementById("sd_free").innerHTML = "Space left: " + 
+            formatBytesMB(storage.free_mb) + " free of " + formatBytesMB(storage.total_mb) +
+            " (" + Math.round(storage.used_mb / storage.total_mb * 100) + "% used)";
+        document.getElementById("sd_speed").innerHTML = "Estimated write speed: " + 
+            (storage.write_speed_bps / 1048576).toFixed(2) + " MB/s";
+    } else {
+        sdStatus.innerHTML = "SD not found";
+        sdStatus.style.color = "red";
+
+        document.getElementById("sd_type").innerHTML = "-";
+        document.getElementById("sd_free").innerHTML = "-";
+        document.getElementById("sd_speed").innerHTML = "-";
+    }
+}
+
 window.onload = connectWebSocket;
 
 </script>
@@ -104,23 +143,27 @@ window.onload = connectWebSocket;
 <body>
 <div class="card">
 <h1>ESP32 Dashboard OTA</h1>
-<p>Device uptime:</p>
+<div id="uptime">Device uptime: Loading...</div>
-<div id="uptime">Loading...</div>
 </div>
 
 <div class="card">
 <h1>Hub Diagnostics:</h1>
-<p>Free heap:</p>
+<div id=free_heap>Free heap: Loading...</div>
-<div id=free_heap>Loading...</div>
+<div id=minimum_free_heap>Minimum free heap: Loading...</div>
-<p>Minimum free heap:</p>
+<div id=cpu_frequency>CPU Frequency: Loading...</div>
-<div id=minimum_free_heap>Loading...</div>
+</div>
-<p>CPU Frequency:</p>
+
-<div id=cpu_frequency>Loading...</div>
+<div class="card">
+<h1>SD Storage:</h1>
+<div id=sd_status>Status: Loading...</div>
+<div id=sd_type>Card type: Loading...</div>
+<div id=sd_free>Space left: Loading...</div>
+<div id=sd_speed>Estimated write speed: Loading...</div>
 </div>
 
 </body>
 <footer>
-Firmware Version: <div id="firmware_version">Loading...</div>
+<div id="firmware_version">Firmware Version: Loading...</div>
 </footer>
 </html>
 )rawliteral";
@@ -128,7 +171,7 @@ Firmware Version: <div id="firmware_version">Loading...</div>
 void WebService::broadcastState()
 {
     DiagnosticSample diagnostics = diagnosticsState.getCurrent();
-    Serial.println(diagnostics.freeHeap);
+    StorageSnapshot storage = storageState.getCurrent();
     String json = "{";
 
     // Opening system tag:
@@ -162,6 +205,35 @@ void WebService::broadcastState()
 
     json += "}"; // Clost diagnostic tag
 
+    // Opening storage tag:
+    json += ",\"storage\":{";
+
+    json += "\"mounted\":\"";
+    json += storage.mounted ? "true" : "false";
+    json += "\",";
+
+    json += "\"card_type\":\"";
+    json += storage.cardType;
+    json += "\",";
+
+    json += "\"total_mb\":\"";
+    json += storage.totalMB;
+    json += "\",";
+
+    json += "\"free_mb\":\"";
+    json += storage.freeMB;
+    json += "\",";
+
+    json += "\"used_mb\":\"";
+    json += storage.usedMB;
+    json += "\",";
+
+    json += "\"write_speed_bps\":\"";
+    json += storage.writeSpeedBps;
+    json += "\"";
+
+    json += "}"; // Close storage tag
+
 
     // Final close bracket
     json += "}";

src/services/web_service.h

@@ -7,12 +7,13 @@
 
 #include "../core/dashboard_state.h"
 #include "../core/diagnostics_state.h"
+#include "../core/storage_state.h"
 
 class WebService : public Service {
 
 public:
 
-    WebService(DashboardState& state, DiagnosticsState& diag_state);
+    WebService(DashboardState& state, DiagnosticsState& diag_state, StorageState& storage_state);
 
     void begin() override;
     void update() override;
@@ -24,6 +25,7 @@ private:
 
     DashboardState& dashboardState;
     DiagnosticsState& diagnosticsState;
+    StorageState& storageState;
 
     void handleWebSocketMessage(uint8_t clientNum, uint8_t *payload, size_t length);
     void broadcastState();

src/storage/sd_manager.cpp

@@ -0,0 +1,443 @@
+#include "sd_manager.h"
+
+#include "storage_config.h"
+
+#include <driver/gpio.h>
+
+// Both backends are compiled into the image so that the SDIO path is
+// compile-checked even while the system still runs SPI for bring-up.
+#include <SD.h>
+#include <SD_MMC.h>
+
+namespace
+{
+
+class SpiBackend : public StorageBackend
+{
+public:
+    bool begin() override
+    {
+        // Explicit SPI instance so the pin wiring is driven from
+        // storage_config.h rather than the board defaults. The second
+        // spi.begin() call made inside SDFS::begin() is a no-op because the
+        // bus is already started with these pins.
+        static SPIClass spi;
+
+        spi.begin(
+            STORAGE_SPI_SCK,
+            STORAGE_SPI_MISO,
+            STORAGE_SPI_MOSI,
+            STORAGE_SPI_CS
+        );
+
+        // Cheap breakout modules often omit the pull-up resistors the SD
+        // spec expects on the idle-high lines. The ESP32 SPI HAL clears the
+        // internal pull-ups when it attaches a pin (esp32-hal-spi.c), so a
+        // floating MISO/CS means the card never answers CMD0 during init
+        // ("Card Failed! cmd: 0x00"). Re-enable the pull-ups directly so we
+        // do not disturb the pin's peripheral function.
+        gpio_pullup_en((gpio_num_t)STORAGE_SPI_MISO);
+        gpio_pullup_en((gpio_num_t)STORAGE_SPI_CS);
+
+        // Give the card a moment to stabilize after power-on before the init
+        // handshake starts (the framework sends 74+ dummy clocks, but some
+        // cards need a little more settling time on a fresh mount attempt).
+        delay(20);
+
+        return SD.begin(
+            STORAGE_SPI_CS,
+            spi,
+            STORAGE_SPI_FREQ,
+            STORAGE_MOUNT_POINT,
+            STORAGE_MAX_OPEN_FILES,
+            false // format_if_empty: never auto-format
+        );
+    }
+
+    void end() override
+    {
+        SD.end();
+    }
+
+    fs::FS& fs() override
+    {
+        return SD;
+    }
+
+    StorageCardType cardType() override
+    {
+        return mapType(SD.cardType());
+    }
+
+    uint64_t totalBytes() override
+    {
+        return SD.totalBytes();
+    }
+
+    uint64_t usedBytes() override
+    {
+        return SD.usedBytes();
+    }
+
+private:
+    static StorageCardType mapType(sdcard_type_t type)
+    {
+        switch (type)
+        {
+        case CARD_MMC:  return StorageCardType::MMC;
+        case CARD_SD:   return StorageCardType::SD;
+        case CARD_SDHC: return StorageCardType::SDHC;
+        case CARD_NONE: return StorageCardType::None;
+        default:        return StorageCardType::Unknown;
+        }
+    }
+};
+
+class SdmmcBackend : public StorageBackend
+{
+public:
+    bool begin() override
+    {
+        // The plain esp32dev variant does not pre-wire the SDMMC pins, so
+        // they must always be set explicitly. The classic ESP32 routes the
+        // SDMMC peripheral through the GPIO matrix, so the pins defined in
+        // storage_config.h are fully re-routable.
+        if (!SD_MMC.setPins(
+                STORAGE_SDMMC_CLK,
+                STORAGE_SDMMC_CMD,
+                STORAGE_SDMMC_D0,
+                STORAGE_SDMMC_D1,
+                STORAGE_SDMMC_D2,
+                STORAGE_SDMMC_D3))
+        {
+            return false;
+        }
+
+        return SD_MMC.begin(
+            STORAGE_MOUNT_POINT,
+            STORAGE_SDMMC_MODE_1BIT,          // false == 4-bit bus
+            STORAGE_SDMMC_FORMAT_IF_FAILED,   // never auto-format
+            STORAGE_SDMMC_FREQ_HZ,            // 40 MHz == SDMMC_FREQ_HIGHSPEED
+            STORAGE_MAX_OPEN_FILES
+        );
+    }
+
+    void end() override
+    {
+        SD_MMC.end();
+    }
+
+    fs::FS& fs() override
+    {
+        return SD_MMC;
+    }
+
+    StorageCardType cardType() override
+    {
+        return mapType(SD_MMC.cardType());
+    }
+
+    uint64_t totalBytes() override
+    {
+        return SD_MMC.totalBytes();
+    }
+
+    uint64_t usedBytes() override
+    {
+        return SD_MMC.usedBytes();
+    }
+
+private:
+    static StorageCardType mapType(sdcard_type_t type)
+    {
+        switch (type)
+        {
+        case CARD_MMC:  return StorageCardType::MMC;
+        case CARD_SD:   return StorageCardType::SD;
+        case CARD_SDHC: return StorageCardType::SDHC;
+        case CARD_NONE: return StorageCardType::None;
+        default:        return StorageCardType::Unknown;
+        }
+    }
+};
+
+} // namespace
+
+
+SDManager::SDManager()
+:
+backend(nullptr),
+mounted(false)
+{
+}
+
+
+bool SDManager::begin()
+{
+    if (mounted)
+    {
+        return true;
+    }
+
+#if STORAGE_IFACE == STORAGE_IFACE_SDMMC
+    backend = new SdmmcBackend();
+#else
+    backend = new SpiBackend();
+#endif
+
+    if (backend == nullptr)
+    {
+        return false;
+    }
+
+    mounted = backend->begin();
+
+    if (!mounted)
+    {
+        Serial.println("[Storage] SD card mount FAILED");
+        delete backend;
+        backend = nullptr;
+    }
+
+    return mounted;
+}
+
+
+void SDManager::end()
+{
+    if (backend != nullptr)
+    {
+        backend->end();
+        delete backend;
+        backend = nullptr;
+    }
+
+    mounted = false;
+}
+
+
+bool SDManager::isMounted() const
+{
+    return mounted;
+}
+
+
+fs::FS& SDManager::fs()
+{
+    return backend->fs();
+}
+
+
+StorageCardType SDManager::cardType() const
+{
+    if (mounted && backend != nullptr)
+    {
+        return backend->cardType();
+    }
+    return StorageCardType::None;
+}
+
+
+const char* SDManager::cardTypeName() const
+{
+    return cardTypeName(cardType());
+}
+
+
+uint64_t SDManager::totalBytes() const
+{
+    if (mounted && backend != nullptr)
+    {
+        return backend->totalBytes();
+    }
+    return 0;
+}
+
+
+uint64_t SDManager::usedBytes() const
+{
+    if (mounted && backend != nullptr)
+    {
+        return backend->usedBytes();
+    }
+    return 0;
+}
+
+
+uint64_t SDManager::freeBytes() const
+{
+    uint64_t total = totalBytes();
+    uint64_t used  = usedBytes();
+    return (total > used) ? (total - used) : 0;
+}
+
+
+uint32_t SDManager::measureWriteSpeed()
+{
+    if (!mounted || backend == nullptr)
+    {
+        return 0;
+    }
+
+    fs::FS& files = backend->fs();
+
+    const char* scratchPath = STORAGE_SPEED_MEASURE_PATH;
+    const size_t bufferSize = 16 * 1024;
+
+    // Remove any leftover from a previous crashed run.
+    files.remove(scratchPath);
+
+    uint8_t* buffer = (uint8_t*)malloc(bufferSize);
+    if (buffer == nullptr)
+    {
+        return 0;
+    }
+
+    memset(buffer, 0xA5, bufferSize);
+
+    File file = files.open(scratchPath, FILE_WRITE);
+    if (!file)
+    {
+        free(buffer);
+        return 0;
+    }
+
+    uint32_t remaining = STORAGE_SPEED_MEASURE_BYTES;
+    uint32_t startUs = micros();
+
+    while (remaining > 0)
+    {
+        size_t toWrite = (remaining < bufferSize) ? remaining : bufferSize;
+        size_t written = file.write(buffer, toWrite);
+
+        if (written == 0)
+        {
+            break;
+        }
+
+        remaining -= written;
+    }
+
+    file.close();
+
+    uint32_t elapsedUs = micros() - startUs;
+    Serial.print("Elapsed microseconds: ");
+    Serial.println(elapsedUs);
+
+    files.remove(scratchPath);
+    free(buffer);
+
+    if (remaining != 0 || elapsedUs == 0)
+    {
+        return 0;
+    }
+
+    uint64_t writtenBytes = (uint64_t)STORAGE_SPEED_MEASURE_BYTES - remaining;
+    return (uint32_t)((writtenBytes * 1000000ULL) / elapsedUs);
+}
+
+
+const char* SDManager::cardTypeName(StorageCardType type)
+{
+    switch (type)
+    {
+    case StorageCardType::MMC:     return "MMC";
+    case StorageCardType::SD:      return "SD";
+    case StorageCardType::SDHC:    return "SDHC";
+    case StorageCardType::Unknown: return "Unknown";
+    case StorageCardType::None:
+    default:                       return "None";
+    }
+}
+
+
+void SDManager::printCardInfo()
+{
+    if (!mounted)
+    {
+        Serial.println("[Storage] Card info unavailable (not mounted)");
+        return;
+    }
+
+    uint64_t total = backend->totalBytes();
+    uint64_t used  = backend->usedBytes();
+    uint64_t free  = (total > used) ? (total - used) : 0;
+
+    Serial.println("----------------------------------------");
+    Serial.println("SD card information");
+    Serial.println("----------------------------------------");
+    Serial.printf("  Type   : %s\n", cardTypeName(backend->cardType()));
+    Serial.printf("  Total  : %llu bytes\n", (unsigned long long)total);
+    Serial.printf("  Used   : %llu bytes\n", (unsigned long long)used);
+    Serial.printf("  Free   : %llu bytes\n", (unsigned long long)free);
+    Serial.println("----------------------------------------");
+}
+
+
+void SDManager::listFiles()
+{
+    if (!mounted)
+    {
+        Serial.println("[Storage] Cannot list files (not mounted)");
+        return;
+    }
+
+    Serial.println("Files on SD card:");
+    Serial.println("----------------------------------------");
+
+    char path[256];
+    snprintf(path, sizeof(path), "/");
+
+    listFilesRecursive(backend->fs(), path, sizeof(path), 0);
+
+    Serial.println("----------------------------------------");
+    Serial.println("End of listing");
+}
+
+
+void SDManager::listFilesRecursive(fs::FS& files, char* path, size_t pathSize, uint8_t depth)
+{
+    if (depth > STORAGE_LIST_MAX_DEPTH)
+    {
+        Serial.printf("  ... (max depth %u reached)\n", STORAGE_LIST_MAX_DEPTH);
+        return;
+    }
+
+    File dir = files.open(path);
+
+    if (!dir)
+    {
+        Serial.printf("  [error] cannot open: %s\n", path);
+        return;
+    }
+
+    if (!dir.isDirectory())
+    {
+        Serial.printf("  %s (%llu bytes)\n", path, (unsigned long long)dir.size());
+        dir.close();
+        return;
+    }
+
+    File entry;
+    while ((entry = dir.openNextFile()))
+    {
+        size_t base = strlen(path);
+
+        if (entry.isDirectory())
+        {
+            snprintf(path + base, pathSize - base, "/%s", entry.name());
+            Serial.printf("  %s/\n", path);
+            listFilesRecursive(files, path, pathSize, depth + 1);
+            path[base] = '\0';
+        }
+        else
+        {
+            snprintf(path + base, pathSize - base, "/%s", entry.name());
+            Serial.printf("  %s (%llu bytes)\n", path, (unsigned long long)entry.size());
+        }
+
+        entry.close();
+    }
+
+    dir.close();
+}

src/storage/sd_manager.h

@@ -0,0 +1,72 @@
+#pragma once
+
+#include <Arduino.h>
+#include <FS.h>
+
+// StorageCardType decouples the rest of the system from the SD/SD_MMC
+// library enum so nothing outside sd_manager.cpp needs to know which
+// hardware interface is in use.
+enum class StorageCardType
+{
+    None,
+    MMC,
+    SD,
+    SDHC,
+    Unknown
+};
+
+// Hardware abstraction for the SD card transport. The concrete backend
+// (SPI today, SDIO later) is selected at build time in storage_config.h.
+// Everything downstream (StorageTask, future DataLogger) talks only to
+// the `fs::FS` reference, so swapping SPI for SDIO touches no other code.
+class StorageBackend
+{
+public:
+    virtual ~StorageBackend() {}
+
+    virtual bool begin() = 0;
+    virtual void end() = 0;
+
+    virtual fs::FS& fs() = 0;
+
+    virtual StorageCardType cardType() = 0;
+    virtual uint64_t totalBytes() = 0;
+    virtual uint64_t usedBytes() = 0;
+};
+
+// Owns the selected backend, mounts the card, and provides the boot-time
+// info/listing report. The mount and any file access are blocking and are
+// expected to be driven from the dedicated StorageTask on core 0.
+class SDManager
+{
+public:
+    SDManager();
+
+    bool begin();
+    void end();
+
+    bool isMounted() const;
+
+    fs::FS& fs();
+
+    StorageCardType cardType() const;
+    const char* cardTypeName() const;
+    uint64_t totalBytes() const;
+    uint64_t usedBytes() const;
+    uint64_t freeBytes() const;
+
+    // Writes a scratch file of STORAGE_SPEED_MEASURE_BYTES and returns the
+    // achieved write throughput in bytes/second (0 on failure). The scratch
+    // file is deleted before returning.
+    uint32_t measureWriteSpeed();
+
+    void printCardInfo();
+    void listFiles();
+
+private:
+    StorageBackend* backend;
+    bool mounted;
+
+    void listFilesRecursive(fs::FS& files, char* path, size_t pathSize, uint8_t depth);
+    static const char* cardTypeName(StorageCardType type);
+};

src/storage/storage_config.h

@@ -0,0 +1,114 @@
+#pragma once
+
+// ============================================================================
+//  Storage configuration
+// ============================================================================
+//
+//  This header is the single place to configure how the Hub talks to the
+//  SD card. Two hardware interfaces are supported by the Arduino-ESP32
+//  framework, and both are implemented behind the StorageBackend interface
+//  in sd_manager.cpp:
+//
+//    STORAGE_IFACE_SPI   - Uses the `SD` library (SPI protocol). This is the
+//                          bring-up path for the current breakout module,
+//                          which only breaks out the 4 SPI lines.
+//                          Max practical throughput: ~1-2 MB/s. NOT enough
+//                          for the 6-8 MB/s audio logging target.
+//
+//    STORAGE_IFACE_SDMMC - Uses the `SD_MMC` library (SDIO protocol, the
+//                          SDMMC peripheral). This is the production path.
+//                          4-bit mode @ 40 MHz (SDMMC_FREQ_HIGHSPEED) gives
+//                          roughly 8-12 MB/s, which comfortably meets the
+//                          target. REQUIRED for the final design.
+//
+//  TO MIGRATE TO SDIO (the new SDIO-capable board that is being shipped):
+//
+//    1. Change STORAGE_IFACE below from STORAGE_IFACE_SPI to
+//       STORAGE_IFACE_SDMMC.
+//
+//    2. Wire the SD card to the SDIO lines listed in the STORAGE_SDMMC_*
+//       defines below. On the classic ESP32 the SDMMC peripheral is routed
+//       through the GPIO matrix, so these pins can be changed to any free
+//       GPIO simply by editing the defines.
+//
+//    3. Keep STORAGE_SDMMC_MODE_1BIT as `false` (4-bit bus is required for
+//       the write throughput) and keep STORAGE_SDMMC_FORMAT_IF_FAILED as
+//       `false` (a foreign/unformatted card must never be auto-formatted).
+//
+//    4. Everything downstream (StorageTask, SDManager, and the future
+//       DataLogger) talks only through the `fs::FS` interface, so no other
+//       code changes are needed.
+// ============================================================================
+
+// --- Backend selection ------------------------------------------------------
+
+#define STORAGE_IFACE_SPI     1
+#define STORAGE_IFACE_SDMMC   2
+
+// SPI until the SDIO-capable board arrives.
+#ifndef STORAGE_IFACE
+#define STORAGE_IFACE STORAGE_IFACE_SPI
+#endif
+
+// --- Common -----------------------------------------------------------------
+
+// Single canonical mount point so file paths never change when the backend
+// is switched (the SD lib defaults to "/sd", SD_MMC to "/sdcard").
+#define STORAGE_MOUNT_POINT      "/sdcard"
+
+#define STORAGE_MAX_OPEN_FILES   5
+
+// --- SPI (bring-up only) ----------------------------------------------------
+
+// Default VSPI pins on the classic ESP32 DevKitC (variant/pins_arduino.h).
+#define STORAGE_SPI_CS     5
+#define STORAGE_SPI_SCK    18
+#define STORAGE_SPI_MOSI   23
+#define STORAGE_SPI_MISO   19
+
+// 10 MHz is a reliable default for breadboard/jumper-wire bring-up. The SD
+// init handshake always runs at 400 kHz regardless (see sd_diskio.cpp), so a
+// mount failure is NOT a frequency problem - check power, wiring, pull-ups
+// and card seating first. Raise to 20 MHz once the wiring is proven.
+#define STORAGE_SPI_FREQ   10000000UL
+
+// --- SDIO / SD_MMC (production, 4-bit) --------------------------------------
+
+// Default ESP32 SDMMC slot-1 pins (GPIO matrix, freely re-routable).
+#define STORAGE_SDMMC_CLK  6
+#define STORAGE_SDMMC_CMD  11
+#define STORAGE_SDMMC_D0   7
+#define STORAGE_SDMMC_D1   8
+#define STORAGE_SDMMC_D2   9
+#define STORAGE_SDMMC_D3   10
+
+// false = 4-bit wide bus (required for >8 MB/s). Do NOT enable 1-bit mode.
+#define STORAGE_SDMMC_MODE_1BIT          false
+
+// NEVER auto-format: an unformatted/foreign card must never be destroyed.
+#define STORAGE_SDMMC_FORMAT_IF_FAILED   false
+
+// 40 MHz == SDMMC_FREQ_HIGHSPEED. Written as a literal to keep this header
+// free of driver includes.
+#define STORAGE_SDMMC_FREQ_HZ            40000000
+
+// --- Boot-time file listing -------------------------------------------------
+
+// Maximum directory depth printed during the recursive boot listing. Guards
+// the StorageTask stack against pathological directory nesting.
+#define STORAGE_LIST_MAX_DEPTH   10
+
+// --- Write-speed estimation -------------------------------------------------
+
+// Path of the temporary scratch file used to measure write throughput. It is
+// created, written, measured, then deleted, so it never appears in listings.
+#define STORAGE_SPEED_MEASURE_PATH   STORAGE_MOUNT_POINT "/.writespeed.tmp"
+
+// Size of the scratch file written per measurement (bytes).
+#define STORAGE_SPEED_MEASURE_BYTES       (0.5 * 1024 * 1024)
+
+// How often to re-measure write speed (ms). This is a bring-up ESTIMATE only:
+// it writes STORAGE_SPEED_MEASURE_BYTES to the card on every tick. Once real
+// logging exists, throughput should be derived from actual logging writes and
+// this benchmark disabled by setting the interval to 0 (measure once at boot).
+#define STORAGE_SPEED_MEASURE_INTERVAL_MS 0

src/tasks/storage_task.cpp

@@ -0,0 +1,98 @@
+#include "storage_task.h"
+
+#include "../storage/storage_config.h"
+
+
+StorageTask::StorageTask(SDManager& manager, StorageState& state)
+:
+storage(manager),
+storageState(state),
+taskHandle(nullptr)
+{
+}
+
+
+void StorageTask::start()
+{
+    // Dedicated task on core 0 so SD card work never blocks the services
+    // running on core 1 (SystemTask / DiagnosticsTask). The 8 KB stack is
+    // sized for the recursive boot-time file listing; the eventual
+    // producer/consumer logging loop will also live here.
+    xTaskCreatePinnedToCore(
+        taskEntry,
+        "StorageTask",
+        8192,
+        this,
+        3,
+        &taskHandle,
+        0
+    );
+}
+
+
+void StorageTask::taskEntry(void* parameter)
+{
+    StorageTask* task =
+        static_cast<StorageTask*>(parameter);
+
+    task->run();
+}
+
+
+void StorageTask::run()
+{
+    Serial.println("[Storage] Initializing SD card...");
+
+    storageState.begin();
+
+    // While the mount has not succeeded the dashboard must show "SD not found".
+    storageState.setMounted(false);
+
+    // Retry the mount until it succeeds. This keeps the card dead-pin-capable:
+    // reseating the card, fixing a wire, or powering the module will bring it
+    // up without rebooting the Hub. (The SD init handshake runs at 400 kHz, so
+    // a failure here is wiring/power/seating/pull-up related, not speed.)
+    while (!storage.begin())
+    {
+        Serial.println("[Storage] SD card mount FAILED.");
+        Serial.println("[Storage] Check: 3.3V power + common ground, CS/SCK/MOSI/MISO wiring,");
+        Serial.println("[Storage]       card fully seated (click), and module pull-ups.");
+        Serial.println("[Storage] Retrying in 5 s...");
+        vTaskDelay(pdMS_TO_TICKS(5000));
+    }
+
+    storageState.setMounted(true);
+    storageState.setCardType(storage.cardTypeName());
+
+    storage.printCardInfo();
+    storage.listFiles();
+
+    // Initial write-speed estimate for the dashboard.
+    storageState.setWriteSpeedBps(storage.measureWriteSpeed());
+    storageState.setCapacity(storage.totalBytes(), storage.usedBytes());
+
+    TickType_t lastWake =
+        xTaskGetTickCount();
+
+    uint32_t lastSpeedMeasure = millis();
+
+    while (true)
+    {
+        // Periodically re-estimate write speed and refresh capacity so the
+        // dashboard stays current. An interval of 0 disables re-measuring.
+        if (STORAGE_SPEED_MEASURE_INTERVAL_MS != 0 &&
+            millis() - lastSpeedMeasure >= STORAGE_SPEED_MEASURE_INTERVAL_MS)
+        {
+            lastSpeedMeasure = millis();
+            storageState.setWriteSpeedBps(storage.measureWriteSpeed());
+            storageState.setCapacity(storage.totalBytes(), storage.usedBytes());
+        }
+
+        // Future integration point: a producer/consumer queue will feed
+        // audio data here to be flushed to the card.
+        vTaskDelayUntil(
+            &lastWake,
+            pdMS_TO_TICKS(1000)
+        );
+    }
+}

src/tasks/storage_task.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <Arduino.h>
+
+#include "../core/storage_state.h"
+#include "../storage/sd_manager.h"
+
+
+class StorageTask
+{
+public:
+    StorageTask(SDManager& manager, StorageState& state);
+
+    void start();
+
+private:
+    static void taskEntry(void* parameter);
+    void run();
+
+    SDManager& storage;
+    StorageState& storageState;
+
+    TaskHandle_t taskHandle = nullptr;
+};