espressif: fix MCUBoot OTA on Espressif devices.

[fdcavalcanti]

Summary

• documentation: update documentation for MCUBoot on Espressif devices
• arch/risc-v: change offset for SPI Flash on Espressif devices
• boards/risc-v: fixes SPI Flash for MCUBoot usage
  Adds partitions required for MCUBoot usage and a sample defconfig.
• arch/xtensa: add E-Fuse support on ESP32S2
  Adds support for e-fuse on ESP32S2 and fixes a gitignore issue.
• boards/xtensa: fixes SPI Flash for MCUBoot usage
  Fixes partitions for MCUBoot usage.

This PR modifies SPI Flash and E-Fuse related code to support OTA using MCUBoot.

Impact

• Impact on user: Yes. Adds and fixes MCUBoot defconfig (mcuboot_update_agent) so the user can execute OTA.
• Impact on build: No.
• Impact on hardware: Affects ESP32|S2|S3|C3|C6 which have Wi-Fi support.
• Impact on documentation: Yes, updates or adds sections to explain how to build and execute OTA.
• Impact on security: No.
• Impact on compatibility: No.

Testing

This example is valid for any of the SoCs affected. Tested on all of them and also CI tested.

Building

Part 1:
First build the default mcuboot_update_agent config. This image defaults to the primary slot and already comes with Wi-Fi settings enabled.

• ./tools/configure.sh esp32-devkitc:mcuboot_update_agent
• make bootloader
• make
• flash

Verify it boots ok and the message This is MCUBoot Update Agent image appears before Nuttshell is ready.

Connect to Wi-Fi:

nsh> wapi psk wlan0 espmint123 3
nsh> wapi essid wlan0 espmint 1
nsh> renew wlan0

Keep the board as is and move to part 2.

Part 2:

On menuconfig, change MCUBoot target slot to the 2nd slot and modify the MOTD as a mean to verify the new image is being used:

kconfig-tweak -d CONFIG_ESPRESSIF_ESPTOOL_TARGET_PRIMARY
kconfig-tweak -e CONFIG_ESPRESSIF_ESPTOOL_TARGET_SECONDARY
kconfig-tweak --set-str CONFIG_NSH_MOTD_STRING "This is MCUBoot UPDATED image!

Apply the changes with make olddefconfig and rebuild with make.

This will build a binary with secondary slot as target and a custom MOTD.

Running

At this point the board is already connected to Wi-Fi and has the primary image flashed. To execute OTA, create a simple HTTP server on the NuttX directory so we can access the binary remotely:

$ cd nuttxspace/nuttx
$ python -m http.server
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...

On the board, execute the update agent, setting the IP address to the one on the host machine:

nsh> mcuboot_agent http://10.42.0.1:8000/nuttx.bin
MCUboot Update Agent example
Downloading from http://10.42.0.1:8000/nuttx.bin
Firmware Update size: 1048576 bytes
Received: 512      of 1048576 bytes [0%]
Received: 1024     of 1048576 bytes [0%]
Received: 1536     of 1048576 bytes [0%]

Wait until image is transferred and the board should reboot automatically:

Application Image successfully downloaded!
Requested update for next boot. Restarting...

Nuttshell should now show the new MOTD:

NuttShell (NSH) NuttX-10.4.0
This is MCUBoot UPDATED image!
nsh> 

At this point, the image is loaded but not confirmed. To make sure it won't rollback to the previous image, you must confirm with mcuboot_confirm and reboot the board. The OTA is now complete.

[fdcavalcanti]

Seems we have an error building esp32-devkitc/mcuboot_update_agent. Works fine locally, I guess MCUBoot download has failed.

Configuration/Tool: esp32-devkitc/mcuboot_update_agent
2025-07-16 16:45:24
------------------------------------------------------------------------------------
  Cleaning...
  Configuring...
  Building NuttX...

make: *** [tools/Unix.mk:559: nuttx] Error 1
make: Target 'all' not remade because of errors.
  [1/1] Normalize esp32-devkitc/mcuboot_update_agent

[xiaoxiang781216]

@fdcavalcanti this error happen in many pr(e.g. this pr and #16734) recently:

 Traceback (most recent call last):
  File "/usr/local/bin/esptool.py", line 37, in <module>
    esptool._main()
  File "/usr/local/lib/python3.10/dist-packages/esptool/__init__.py", line 1170, in _main
    main()
  File "/usr/local/lib/python3.10/dist-packages/esptool/__init__.py", line 983, in main
    operation_func(args)
  File "/usr/local/lib/python3.10/dist-packages/esptool/cmds.py", line 1097, in elf2image
    image.save(args.output)
  File "/usr/local/lib/python3.10/dist-packages/esptool/bin_image.py", line 778, in save
    assert (f.tell() + 8 + self.ROM_LOADER.BOOTLOADER_FLASH_OFFSET) % (
AssertionError
make: *** [tools/Unix.mk:559: nuttx] Error 1
make: Target 'all' not remade because of errors.
  [1/1] Normalize esp32-devkitc/nxlooper

please fix it.

[acassis]

@fdcavalcanti please update https://nuttx.apache.org/docs/latest/platforms/xtensa/esp32/boards/esp32-devkitc/index.html#mcuboot-update-agent to include the steps you included here. This will make life easier for those is testing it.

[fdcavalcanti]

@fdcavalcanti please update https://nuttx.apache.org/docs/latest/platforms/xtensa/esp32/boards/esp32-devkitc/index.html#mcuboot-update-agent to include the steps you included here. This will make life easier for those is testing it.

Do you mean the link to the video?

[xiaoxiang781216]

@fdcavalcanti please fix the conflict

[acassis]

@fdcavalcanti please update https://nuttx.apache.org/docs/latest/platforms/xtensa/esp32/boards/esp32-devkitc/index.html#mcuboot-update-agent to include the steps you included here. This will make life easier for those is testing it.

Do you mean the link to the video?

No, I mean the Testing steps that you included here. This way users could test it locally

[fdcavalcanti]

@fdcavalcanti please update https://nuttx.apache.org/docs/latest/platforms/xtensa/esp32/boards/esp32-devkitc/index.html#mcuboot-update-agent to include the steps you included here. This will make life easier for those is testing it.

Do you mean the link to the video?

No, I mean the Testing steps that you included here. This way users could test it locally

It's still there, just linked to a different section: here