Storage: poll the SD card on its own task

A failed mount retries for ~2.5 s, which froze the UI every 15 s while
no card was inserted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/main.cpp

@@ -35,7 +35,7 @@ static void draw() {
     d.setTextColor(TFT_WHITE);
 
     const auto& b = battery->estimator();
-    const auto& s = storage->state();
+    const auto s = storage->state();
     int y = 16;
     auto line = [&](const String& text) {
         d.drawString(text, 4, y);
@@ -122,7 +122,7 @@ void loop() {
 
     if (millis() - lastLog > 5000) {
         lastLog = millis();
-        const auto& s = storage->state();
+        const auto s = storage->state();
         Serial.printf("status: batt %d%% %dmV raw %d | sd %s %d%% total %lluMB | heap %u min %u | screen %d\n",
                       battery->estimator().percent(), battery->estimator().millivolts(),
                       battery->lastRawMillivolts(), s.present ? "yes" : "no", s.usedPercent,

src/services/storage_service.cpp

@@ -7,11 +7,40 @@
 
 namespace roro {
 
+void StorageService::start() {
+    if (task_) return;
+    lock_ = xSemaphoreCreateMutex();
+    xTaskCreate(taskEntry, "storage", 4096, this, 1, &task_);
+}
+
+void StorageService::stop() {
+    if (!task_) return;
+    vTaskDelete(task_);
+    task_ = nullptr;
+    if (mounted_) SD.end();
+    mounted_ = false;
+}
+
+StorageState StorageService::state() const {
+    xSemaphoreTake(lock_, portMAX_DELAY);
+    StorageState copy = monitor_.state();
+    xSemaphoreGive(lock_);
+    return copy;
+}
+
+void StorageService::taskEntry(void* self) {
+    auto* service = static_cast<StorageService*>(self);
+    for (;;) {
+        service->poll();
+        vTaskDelay(pdMS_TO_TICKS(kPollMs));
+    }
+}
+
 bool StorageService::mount() {
     return SD.begin(pins::kSdCs, sharedSpi(), 20000000, "/sd", 5, false);
 }
 
-void StorageService::tick(uint32_t) {
+void StorageService::poll() {
     if (mounted_) {
         // Detect removal: the root can no longer be opened.
         File root = SD.open("/");
@@ -22,15 +51,13 @@ void StorageService::tick(uint32_t) {
     }
     if (!mounted_) mounted_ = mount();
 
-    if (mounted_)
-        monitor_.update(true, SD.totalBytes(), SD.usedBytes());
-    else
-        monitor_.update(false, 0, 0);
-}
+    bool present = mounted_;
+    uint64_t total = present ? SD.totalBytes() : 0;
+    uint64_t used = present ? SD.usedBytes() : 0;
 
-void StorageService::stop() {
-    if (mounted_) SD.end();
-    mounted_ = false;
+    xSemaphoreTake(lock_, portMAX_DELAY);
+    monitor_.update(present, total, used);
+    xSemaphoreGive(lock_);
 }
 
 }  // namespace roro

src/services/storage_service.h

@@ -1,25 +1,34 @@
 #pragma once
 
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+
 #include "service.h"
 #include "storage_monitor.h"
 
 namespace roro {
 
 // Mounts the microSD card (retrying while absent) and feeds its usage to the StorageMonitor.
+// Runs on its own task: a failed mount blocks for seconds and must never stall the UI.
 class StorageService : public Service {
    public:
     explicit StorageService(EventBus& bus) : monitor_(bus) {}
     const char* name() const override { return "storage"; }
-    uint32_t tickIntervalMs() const override { return 15000; }
-    void tick(uint32_t nowMs) override;
+    void start() override;
     void stop() override;
 
-    const StorageState& state() const { return monitor_.state(); }
+    StorageState state() const;
 
    private:
+    static constexpr uint32_t kPollMs = 15000;
+    static void taskEntry(void* self);
+    void poll();
     bool mount();
+
     StorageMonitor monitor_;
     bool mounted_ = false;
+    TaskHandle_t task_ = nullptr;
+    mutable SemaphoreHandle_t lock_ = nullptr;
 };
 
 }  // namespace roro