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Commit 760e92f186fb1467b5e2f8dbf13d568c31979a60

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Parents : 8561e9d
Author : James L <jrl290@gmail.com>
Date : 2026-02-22T21:24:06-05:00

Fix flash address detection: use bootloader magic byte, not file size

The merged binary (1,257,328 bytes) was below the 1.5MB size threshold,
causing it to be misidentified as app-only and flashed at 0x10000 instead
of 0x0. This corrupted the flash layout and bricked the device.

Now checks for ESP32 bootloader magic byte (0xE9) at offset 0 to reliably
distinguish merged binaries from app-only binaries, regardless of size.

Changes

1 files changed, 17 insertions(+), 3 deletions(-)

M flash.py +17 -3

Diff

diff --git a/flash.py b/flash.py
index 6a5108e..9eb47e2 100644
--- a/flash.py
+++ b/flash.py
@@ -265,13 +265,27 @@ def flash_firmware(firmware_path, port, esptool_cmd, baud=BAUD_RATE):
print(f" Chip: {CHIP} Baud: {baud} Flash: {FLASH_SIZE}\n")
# Determine if this is a merged binary (flash at 0x0) or app-only (flash at 0x10000)
+ # The app-only .bin for this project is ~800KB. The merged binary adds
+ # bootloader+partitions+boot_app0 padding (~64KB) so it's slightly larger
+ # but still well under 2MB. A true app-only binary won't have the bootloader
+ # signature at offset 0. Check for the ESP32 bootloader magic byte (0xE9).
size = os.path.getsize(firmware_path)
- if size > 1500000:
- # Merged binary — includes bootloader, partitions, etc.
+ is_merged = False
+ try:
+ with open(firmware_path, "rb") as f:
+ magic = f.read(1)
+ if magic == b'\xe9':
+ # Has bootloader magic — this is a merged binary starting at 0x0
+ is_merged = True
+ except Exception:
+ pass
+
+ if is_merged:
flash_addr = f"0x{BOOTLOADER_ADDR:x}"
+ print(f" Detected: merged binary (bootloader magic 0xE9) → flash at {flash_addr}")
else:
- # App-only binary
flash_addr = f"0x{APP_ADDR:x}"
+ print(f" Detected: app-only binary → flash at {flash_addr}")
cmd = esptool_cmd + [
"--chip", CHIP,

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