Add support for building MCUboot bootloader

.github/workflows/build.yml

@@ -7,10 +7,14 @@ jobs:
     runs-on: ubuntu-20.04
     steps: 
       - uses: actions/checkout@v1
-      - name: Build bootloader and partition table
+      - name: Build IDF bootloader and partition table
         uses: docker://docker.io/espressif/idf:release-v4.3
         with:
-          args: ./build.sh
+          args: ./build_idfboot.sh
+      - name: Build MCUboot bootloader
+        uses: docker://docker.io/espressif/idf:release-v4.3
+        with:
+          args: ./build_mcuboot.sh
       - name: Update release
         if: "github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/')"
         uses: eine/tip@master

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "mcuboot"]
+	path = mcuboot
+	url = https://github.com/mcu-tools/mcuboot.git

README.md

@@ -1,43 +1,83 @@
 [![Build Status](https://github.com/espressif/esp-nuttx-bootloader/workflows/build/badge.svg)](https://github.com/espressif/esp-nuttx-bootloader/actions?query=branch%3Amain)
 
-# Bootloader and partition table for NuttX
+# Bootloader for NuttX
 
-This repository contains a minimal ESP-IDF project and build scripts used to produce 2nd stage bootloader and partition table binaries. Users of NuttX RTOS can download the binaries from release artifacts in this repository.
+This repository contains build scripts for producing the binaries for the 2nd stage bootloader. There are two bootloader options:
+- [IDF bootloader](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/startup.html#second-stage-bootloader) (**default** option for NuttX images)
+- [MCUboot bootloader](https://github.com/mcu-tools/mcuboot/blob/main/docs/readme-espressif.md) (for loading NuttX images built with `CONFIG_ESP32_APP_FORMAT_MCUBOOT` option)
 
-# Obtaining the binaries
+Users of NuttX RTOS can download the binaries from release artifacts in this repository.
 
-## Downloading the latest version from Github
+# Downloading the latest version from Github
 
-Binaries built from the tip of the default branch or this repository can be obtained here:
+Binaries built from the tip of the default branch of this repository can be obtained here:
+
+## IDF bootloader
 
 Chip | Bootloader | Partition table
 -----|------------|-----------------
 ESP32 | [bootloader-esp32.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/bootloader-esp32.bin) | [partition-table-esp32.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/partition-table-esp32.bin)
 ESP32-S2 | [bootloader-esp32s2.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/bootloader-esp32s2.bin) | [partition-table-esp32s2.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/partition-table-esp32s2.bin)
 ESP32-C3 | [bootloader-esp32c3.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/bootloader-esp32c3.bin) | [partition-table-esp32c3.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/partition-table-esp32c3.bin)
 
-## Building locally
+## MCUboot bootloader
+
+Chip | Bootloader
+-----|------------
+ESP32 | [mcuboot-esp32.bin](https://github.com/espressif/esp-nuttx-bootloader/releases/download/latest/mcuboot-esp32.bin)
+
+The prebuilt bootloader image considers the following default partitioning of the chip's SPI Flash for the application slots:
+
+Attribute | Value
+----------|-------
+Application Primary slot offset | 0x10000
+Application Secondary slot offset | 0x110000
+Application slot size | 0x100000 (1 MiB)
+Scratch slot offset | 0x210000
+Scratch slot size | 0x40000 (256 KiB)
+
+# Building locally
 
-To build the binaries locally, it is recommended to run [build.sh](build.sh) script inside `espressif/idf` Docker image:
+## IDF bootloader
+
+It is recommended to build the binaries inside the `espressif/idf` Docker image.
 
 ```bash
 git clone https://github.com/espressif/esp-nuttx-bootloader.git
 cd esp-nuttx-bootloader
-docker run --rm -v $PWD:/work -w /work espressif/idf:release-v4.3 ./build.sh
+docker run --rm -v $PWD:/work -w /work espressif/idf:release-v4.3 ./build_idfboot.sh
 ```
 
 The binaries will be inside `out` directory.
 
-## Modifying sdkconfig or the partition table
+### Modifying sdkconfig or the partition table
 
 When building locally, you can customize bootloader configuration and the partition table by editing [sdkconfig.defaults](sdkconfig.defaults) and [partitions.csv](partitions.csv) files.
 
 For more information about these files, refer to the following chapters of IDF Programming Guide:
 
-* [Partition Tables](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-guides/partition-tables.html) 
+* [Partition Tables](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-guides/partition-tables.html)
 * [Bootloader](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-guides/bootloader.html)
 * [Configuration Options Reference](https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/kconfig.html#configuration-options-reference)
 
+
+## MCUboot bootloader
+
+It is recommended to build the binaries inside the `espressif/idf` Docker image.
+
+```bash
+git clone https://github.com/espressif/esp-nuttx-bootloader.git
+cd esp-nuttx-bootloader
+docker run --rm -v $PWD:/work -w /work espressif/idf:release-v4.3 ./build_mcuboot.sh
+```
+
+The binaries will be inside `out` directory.
+
+### Modifying the application slots attributes
+
+When building locally, you may customize the bootloader default attributes by editing [mcuboot.conf](mcuboot.conf) file.
+Remember to mirror the customized configuration on the application firmware image.
+
 # License
 
 This repository and the binaries on the Releases page are distributed under Apache 2.0, the same as the license of ESP-IDF.

build_mcuboot.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+#
+#  Copyright (c) 2021 Espressif Systems (Shanghai) Co., Ltd.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+set -euo pipefail
+
+targets="esp32"
+mcuboot_config="${PWD}/mcuboot.conf"
+output_dir="${PWD}/out"
+
+mkdir -p "${output_dir}"
+
+git submodule update --init mcuboot
+pushd mcuboot &>/dev/null
+
+git submodule update --init --recursive ext/mbedtls
+cd boot/espressif
+
+for target in ${targets}; do
+    cmake -DCMAKE_TOOLCHAIN_FILE=tools/toolchain-"${target}".cmake -DMCUBOOT_TARGET="${target}" -DMCUBOOT_CONFIG_FILE="${mcuboot_config}" -DIDF_PATH="${IDF_PATH}" -B build -GNinja
+    cmake --build build/
+    "${IDF_PATH}"/components/esptool_py/esptool/esptool.py --chip "${target}" elf2image --flash_mode dio --flash_freq 40m -o build/mcuboot-"${target}".bin build/mcuboot_"${target}".elf
+    cp build/mcuboot-"${target}".bin "${output_dir}"/mcuboot-"${target}".bin
+done
+
+popd &>/dev/null

mcuboot.conf

@@ -0,0 +1,7 @@
+CONFIG_ESP_BOOTLOADER_SIZE=0xF000
+CONFIG_ESP_APPLICATION_PRIMARY_START_ADDRESS=0x10000
+CONFIG_ESP_APPLICATION_SIZE=0x100000
+CONFIG_ESP_APPLICATION_SECONDARY_START_ADDRESS=0x110000
+CONFIG_ESP_MCUBOOT_WDT_ENABLE=y
+CONFIG_ESP_SCRATCH_OFFSET=0x210000
+CONFIG_ESP_SCRATCH_SIZE=0x40000