ESP32 Flash Size Detection Error

Common Causes

🧩
Incorrect Flash Size Setting in IDE
If the selected flash size in Arduino IDE or PlatformIO doesn’t match the actual hardware, the ESP32 may fail to boot or flash properly.
💾
Board with Non-Standard Flash Size
Some ESP32 boards, especially clones, may use smaller or unusual flash chips that require manual configuration.
⚠️
Flash Configuration Corrupted by Previous Upload
A failed or mismatched upload can leave the flash in an inconsistent state, causing further upload failures.

Symptoms

Upload Fails with Flash Size or Partition Errors

The serial monitor or IDE shows messages about flash size mismatch, partition errors, or inability to write flash.

Board Boots But Resets or Freezes

Even if upload completes, the board may not boot or may crash due to incompatible flash layout assumptions.

Serial Output Shows Reboot Loops or Memory Faults

Serial monitor may show repeating crashes or decoding failures linked to incorrect flash region usage.

Solutions

Reset to Default Partition Scheme

Use a standard partition layout (e.g., 4MB with SPIFFS or Default) unless you’re certain a custom scheme is required.

Match Flash Size to Board Specification

Check your ESP32 board’s datasheet or manufacturer page and configure the correct flash size in the IDE.

Erase Flash Before Upload

Perform a full flash erase before re-uploading your sketch to avoid conflicts with previous configurations.

Try a Basic Sketch After Reset

Upload a minimal example like Blink to verify board function and isolate flash size mismatch from code-related errors.

More Details

ESP32 Flash Size Detection Error #

If you're seeing errors during upload or your ESP32 fails to boot after flashing, you might be dealing with a flash size configuration mismatch. Each ESP32 module has a specific flash chip size, and setting it incorrectly in your development environment can cause serious issues — from failed uploads to infinite reboot loops.

Common Symptoms #

Upload fails with errors like

flash size does not match

or

Invalid partition table

The sketch appears to upload but the ESP32 keeps rebooting
Serial monitor shows

Guru Meditation Error

watchdog resets, or corrupted memory access

Works on one board, fails on another that “looks the same”

Why This Happens #

🧩 Flash Size Mismatch in the IDE #

In Arduino IDE or PlatformIO, you must select the correct flash size for your board. If you choose 4MB but the board has only 2MB, upload or execution will fail.

💾 Clones with Unusual Flash Chips #

Some lower-cost ESP32 boards ship with smaller flash chips (e.g., 1MB or 2MB instead of 4MB or 8MB). These need matching configuration.

⚠️ Leftover Partition Table or Corrupted Flash #

Uploading code built for the wrong flash size can leave the flash in a bad state, with mismatched bootloaders or invalid partition schemes.

How to Fix It #

✅ 1. Check Your Board’s Flash Size
Refer to your board’s documentation or label. Common sizes:

ESP32-WROOM-32: 4MB
ESP32-WROVER: 8MB or 16MB
Some clones: 2MB or even 1MB

Find your ESP32 Board

✅ 2. Select the Correct Flash Configuration in IDE

In Arduino IDE:

Tools → Flash Size → Select the correct size (e.g., 4MB (32Mb) with default partition)

ESP32 Select Flash Size in Arduino IDE

In PlatformIO:

board_build.flash_size = 4MB

✅ 3. Erase Flash Before Uploading

Use esptool.py or your IDE’s erase option:

esptool.py --port COMx erase_flash

Then upload again. This prevents partition mismatches.

✅ 4. Upload a Basic Sketch

Try uploading Blink.ino or another minimal sketch. If it runs properly, the issue was likely with your previous code’s partitioning or flash configuration.

✅ 5. Use Default Partition Schemes Unless Needed

Avoid custom partition tables unless you know exactly what you're doing. Misaligned partitions can corrupt execution or cause boot loops.

Serial Monitor Example #

Invalid head of packet (0x50)
A fatal error occurred: Failed to connect to ESP32
...
ets Jun  8 2016 00:22:57

rst:0x10 (RTCWDT_RTC_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
...
Guru Meditation Error: Core  0 panic'ed (InstrFetchProhibited)

These kinds of messages often point to mismatches in flash layout vs. what the ESP32 expects.

Summary #

Incorrect flash configuration is a silent killer — your code may compile and upload, but fail miserably on execution. Always match your IDE settings to your board’s actual flash size, use safe default partitions, and clear the flash if something seems off.