Fix for legacy ESP8266 bootloader which allows OTA updates with 8MB or 16MB flash map.
The ESP8266 NONOS SDK, as well as RTOS SDK v1.x/v2.x, rely on the legacy bootloader provided as a binary blob.
Unfortunately, it has a bug that prevents OTA updates when the 8MB or 16MB flash map is used. This repository provides a
patched boot_v1.7bigflash.bin that is a drop-in replacement for boot_v1.7.bin bootloader and enables OTA updates
with any flash size, without the need to change any user code.
The patch works by inserting a small assembly stub into an unused part of the original bootloader. See fixboot.s for details. It was developed by partially reverse-engineering the bootloader to identify and fix the problem. The following resources were very helpful:
- Decompiling the ESP8266 boot loader v1.3(b3)
- ESP8266 16MB Flash Handling
- An short guide to Xtensa assembly language
If you don't like binary blobs, check out MBoot which is also a drop-in replacement
for boot_v1.7bin, but is fully open source.
Note: NONOS SDK and RTOS SDK v1.x/v2.x are deprecated. You should use RTOS SDK v3.x for new projects.
The compiled binary is available on the Releases page. If you want to
build it yourself, you'll need the ESP8266 toolchain (version 4.8.5 is recommended). On Windows, a compatibility layer
such as MSYS2 is required. For installation instructions, refer to
RTOS SDK docs.
Make sure xtensa-lx106-elf/bin is added to the PATH environment variable.
Once you have the toolchain installed, run ./fixboot.sh (on Windows use the MSYS2 shell). On successful completion,
the script should print DONE.
When flashing the ESP8266, simply use boot_v1.7bigflash.bin instead of boot_v1.7.bin. The regular NONOS SDK or RTOS
SDK v1.x/v2.x OTA update process should work without issues.
This project is released under the Apache-2.0 license. The boot_v1.7.bin file was taken from the
ESP8266 RTOS SDK repository which is released under the
Apache-2.0 license.