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fix: guard Serial input calls when USB not connected at boot

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Fixes device hanging when booted without USB connected. The root cause
was calling Serial.available() and Serial.read() in checkForFlashCommand()
when Serial.begin() was never called (USB not connected at boot).

Changes:
- Add if (!Serial) return guard to checkForFlashCommand()
- Restore upstream while (!Serial) wait loop with 3s timeout
- Remove Serial.setTxTimeoutMs(0) (not in upstream, may cause issues)
- Remove unnecessary if (Serial) guards from EpubReaderActivity.cpp
  (Serial.printf is safe without guards, only input calls need them)

Key insight: Serial.printf() is safe without guards (returns 0 when not
initialized), but Serial.available()/Serial.read() cause undefined
behavior on ESP32-C3 USB CDC when called without Serial.begin().

See: claude_notes/usb-serial-blocking-fix-2026-01-28.md
This commit is contained in:
cottongin
2026-01-28 17:45:00 -05:00
parent 4965e63ad4
commit ffe2aebd7e
3 changed files with 158 additions and 38 deletions
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52
src/activities/reader/EpubReaderActivity.cpp
View File

@@ -127,9 +127,8 @@ void EpubReaderActivity::onEnter() {
nextPageNumber = pageNumber;
hasContentOffset = true;
if (Serial)
Serial.printf("[%lu] [ERS] Loaded progress v1: spine %d, page %d, offset %u\n", millis(), currentSpineIndex,
nextPageNumber, savedContentOffset);
Serial.printf("[%lu] [ERS] Loaded progress v1: spine %d, page %d, offset %u\n", millis(), currentSpineIndex,
nextPageNumber, savedContentOffset);
} else {
// Unknown version, try legacy format
f.seek(0);
@@ -138,9 +137,8 @@ void EpubReaderActivity::onEnter() {
currentSpineIndex = data[0] + (data[1] << 8);
nextPageNumber = data[2] + (data[3] << 8);
hasContentOffset = false;
if (Serial)
Serial.printf("[%lu] [ERS] Loaded legacy progress (unknown version %d): spine %d, page %d\n", millis(),
version, currentSpineIndex, nextPageNumber);
Serial.printf("[%lu] [ERS] Loaded legacy progress (unknown version %d): spine %d, page %d\n", millis(),
version, currentSpineIndex, nextPageNumber);
}
}
} else if (fileSize >= 4) {
@@ -150,9 +148,8 @@ void EpubReaderActivity::onEnter() {
currentSpineIndex = data[0] + (data[1] << 8);
nextPageNumber = data[2] + (data[3] << 8);
hasContentOffset = false;
if (Serial)
Serial.printf("[%lu] [ERS] Loaded legacy progress: spine %d, page %d\n", millis(), currentSpineIndex,
nextPageNumber);
Serial.printf("[%lu] [ERS] Loaded legacy progress: spine %d, page %d\n", millis(), currentSpineIndex,
nextPageNumber);
}
}
f.close();
@@ -164,9 +161,8 @@ void EpubReaderActivity::onEnter() {
int textSpineIndex = epub->getSpineIndexForTextReference();
if (textSpineIndex != 0) {
currentSpineIndex = textSpineIndex;
if (Serial)
Serial.printf("[%lu] [ERS] Opened for first time, navigating to text reference at index %d\n", millis(),
textSpineIndex);
Serial.printf("[%lu] [ERS] Opened for first time, navigating to text reference at index %d\n", millis(),
textSpineIndex);
}
}
@@ -639,8 +635,7 @@ void EpubReaderActivity::renderScreen() {
if (!section) {
const auto filepath = epub->getSpineItem(currentSpineIndex).href;
if (Serial)
Serial.printf("[%lu] [ERS] Loading file: %s, index: %d\n", millis(), filepath.c_str(), currentSpineIndex);
Serial.printf("[%lu] [ERS] Loading file: %s, index: %d\n", millis(), filepath.c_str(), currentSpineIndex);
section = std::unique_ptr<Section>(new Section(epub, currentSpineIndex, renderer));
const uint16_t viewportWidth = renderer.getScreenWidth() - orientedMarginLeft - orientedMarginRight;
@@ -651,7 +646,7 @@ void EpubReaderActivity::renderScreen() {
if (!section->loadSectionFile(SETTINGS.getReaderFontId(), SETTINGS.getReaderLineCompression(),
SETTINGS.extraParagraphSpacing, SETTINGS.paragraphAlignment, viewportWidth,
viewportHeight, SETTINGS.hyphenationEnabled)) {
if (Serial) Serial.printf("[%lu] [ERS] Cache not found, building...\n", millis());
Serial.printf("[%lu] [ERS] Cache not found, building...\n", millis());
sectionWasReIndexed = true;
// Progress bar dimensions
@@ -697,12 +692,12 @@ void EpubReaderActivity::renderScreen() {
if (!section->createSectionFile(SETTINGS.getReaderFontId(), SETTINGS.getReaderLineCompression(),
SETTINGS.extraParagraphSpacing, SETTINGS.paragraphAlignment, viewportWidth,
viewportHeight, SETTINGS.hyphenationEnabled, progressSetup, progressCallback)) {
if (Serial) Serial.printf("[%lu] [ERS] Failed to persist page data to SD\n", millis());
Serial.printf("[%lu] [ERS] Failed to persist page data to SD\n", millis());
section.reset();
return;
}
} else {
if (Serial) Serial.printf("[%lu] [ERS] Cache found, skipping build...\n", millis());
Serial.printf("[%lu] [ERS] Cache found, skipping build...\n", millis());
}
// Determine the correct page to display
@@ -714,9 +709,8 @@ void EpubReaderActivity::renderScreen() {
// Use the offset to find the correct page
const int restoredPage = section->findPageForContentOffset(savedContentOffset);
section->currentPage = restoredPage;
if (Serial)
Serial.printf("[%lu] [ERS] Restored position via offset: %u -> page %d (was page %d)\n", millis(),
savedContentOffset, restoredPage, nextPageNumber);
Serial.printf("[%lu] [ERS] Restored position via offset: %u -> page %d (was page %d)\n", millis(),
savedContentOffset, restoredPage, nextPageNumber);
// Clear the offset flag since we've used it
hasContentOffset = false;
} else {
@@ -728,7 +722,7 @@ void EpubReaderActivity::renderScreen() {
renderer.clearScreen();
if (section->pageCount == 0) {
if (Serial) Serial.printf("[%lu] [ERS] No pages to render\n", millis());
Serial.printf("[%lu] [ERS] No pages to render\n", millis());
renderer.drawCenteredText(UI_12_FONT_ID, 300, "Empty chapter", true, EpdFontFamily::BOLD);
renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
renderer.displayBuffer();
@@ -736,9 +730,8 @@ void EpubReaderActivity::renderScreen() {
}
if (section->currentPage < 0 || section->currentPage >= section->pageCount) {
if (Serial)
Serial.printf("[%lu] [ERS] Page out of bounds: %d (max %d)\n", millis(), section->currentPage,
section->pageCount);
Serial.printf("[%lu] [ERS] Page out of bounds: %d (max %d)\n", millis(), section->currentPage,
section->pageCount);
renderer.drawCenteredText(UI_12_FONT_ID, 300, "Out of bounds", true, EpdFontFamily::BOLD);
renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
renderer.displayBuffer();
@@ -748,7 +741,7 @@ void EpubReaderActivity::renderScreen() {
{
auto p = section->loadPageFromSectionFile();
if (!p) {
if (Serial) Serial.printf("[%lu] [ERS] Failed to load page from SD - clearing section cache\n", millis());
Serial.printf("[%lu] [ERS] Failed to load page from SD - clearing section cache\n", millis());
section->clearCache();
section.reset();
return renderScreen();
@@ -756,7 +749,7 @@ void EpubReaderActivity::renderScreen() {
// Handle empty pages (e.g., from malformed chapters that couldn't be parsed)
if (p->elements.empty()) {
if (Serial) Serial.printf("[%lu] [ERS] Page has no content (possibly malformed chapter)\n", millis());
Serial.printf("[%lu] [ERS] Page has no content (possibly malformed chapter)\n", millis());
renderer.drawCenteredText(UI_12_FONT_ID, 280, "Chapter content unavailable", true, EpdFontFamily::BOLD);
renderer.drawCenteredText(UI_10_FONT_ID, 320, "(File may be malformed)");
renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
@@ -766,7 +759,7 @@ void EpubReaderActivity::renderScreen() {
const auto start = millis();
renderContents(std::move(p), orientedMarginTop, orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
if (Serial) Serial.printf("[%lu] [ERS] Rendered page in %dms\n", millis(), millis() - start);
Serial.printf("[%lu] [ERS] Rendered page in %dms\n", millis(), millis() - start);
}
// Save progress with content offset for position restoration after re-indexing
@@ -782,9 +775,8 @@ void EpubReaderActivity::renderScreen() {
serialization::writePod(f, contentOffset);
f.close();
if (Serial)
Serial.printf("[%lu] [ERS] Saved progress: spine %d, page %d, offset %u\n", millis(), currentSpineIndex,
section->currentPage, contentOffset);
Serial.printf("[%lu] [ERS] Saved progress: spine %d, page %d, offset %u\n", millis(), currentSpineIndex,
section->currentPage, contentOffset);
}
}