This repository provides the integration scripts to build a complete standalone SDK (with toolchain) for software development with the Espressif ESP31b and ESP32 chips.

The complete SDK consists of:

1. esp108 architecture toolchain (100% OpenSource), based on https://github.com/jcmvbkbc/crosstool-NG

2. ESP32 RTOS SDK from Espressif Systems. This component is only partially open source, (some libraries are provided as binary blobs).

   • https://github.com/espressif/ESP32_RTOS_SDK

To build the standalone SDK and toolchain, you need a GNU/POSIX system (Linux, BSD, MacOSX, Windows with Cygwin) with the standard GNU development tools installed: bash, gcc, binutils, flex, bison, etc.

Please make sure that the machine you use to build the toolchain has at least 1G free RAM+swap (or more, which will speed up the build).

Ubuntu 14.04:

$ sudo apt-get install make unrar autoconf automake libtool gcc g++ gperf \
    flex bison texinfo gawk ncurses-dev libexpat-dev python python-serial sed \
    git unzip bash help2man

Later Debian/Ubuntu versions may require:

$ sudo apt-get install libtool-bin

$ brew tap homebrew/dupes
$ brew install binutils coreutils automake wget gawk libtool gperf gnu-sed --with-default-names grep
$ export PATH="/usr/local/opt/gnu-sed/libexec/gnubin:$PATH"

In addition to the development tools MacOS needs a case-sensitive filesystem. You might need to create a virtual disk and build esp-open-sdk on it:

$ sudo hdiutil create ~/Documents/case-sensitive.dmg -volname "case-sensitive" -size 10g -fs "Case-sensitive HFS+"
$ sudo hdiutil mount ~/Documents/case-sensitive.dmg
$ cd /Volumes/case-sensitive

Be sure to clone recursively:

$ git clone -b esp32 --recursive https://github.com/sermus/esp-open-sdk.git

The project can be built in two modes:

1. Where the toolchain and tools are kept separate from the vendor IoT SDK which contains binary blobs. This makes licensing more clear, and helps facilitate upgrades to vendor SDK releases.

2. A completely standalone ESP31b/32 SDK with the vendor SDK files merged into the toolchain. This mode makes it easier to build software (no additinal -I and -L flags are needed), but redistributability of this build is unclear and upgrades to newer vendor SDK releases are complicated. This mode is default for local builds. Note that if you want to redistribute the binary toolchain built with this mode, you should:

   1. Make it clear to your users that the release is bound to a particular vendor SDK and provide instructions how to upgrade to a newer vendor SDK releases.
   2. Abide by licensing terms of the vendor SDK.

To build the self-contained, standalone toolchain+SDK:

$ make STANDALONE=y

This is the default choice which most people are looking for, so just the following is enough:

$ make

To build the bare Xtensa toolchain and leave ESP8266 SDK separate:

$ make STANDALONE=n

This will download all necessary components and compile them.

Once you complete build process as described above, the toolchain (with the Xtensa HAL library) will be available in the xtensa-esp108-elf/ subdirectory. Add xtensa-esp108-elf/bin/ subdirectory to your PATH environment variable to execute xtensa-esp108-elf-gcc and other tools. At the end of build process, the exact command to set PATH correctly for your case will be output. You may want to save it, as you'll need the PATH set correctly each time you compile for Xtensa/ESP.

ESP32 RTOS SDK will be installed in sdk/. If you chose the non-standalone SDK, run the compiler with the corresponding include and lib dir flags:

$ xtensa-esp108-elf-gcc -I$(THISDIR)/sdk/include      \
                        -I$(THISDIR)/sdk/lwip         \
                        -I$(THISDIR)/sdk/lwip/ipv4    \
                        -I$(THISDIR)/sdk/lwip/ipv6    \
                        -I$(THISDIR)/sdk/espressif    \
                        -L$(THISDIR)/sdk/lib 

If you use SDK in the standlone mode you need to build with these additional -I options (you may refer to the example Makefile in examples/rtos_hello_world and examples/esp_sgi_stl_tests)

$ xtensa-esp108-elf-gcc -I$(SYSROOT_HEADERS)/lwip         \
                        -I$(SYSROOT_HEADERS)/lwip/ipv4    \
                        -I$(SYSROOT_HEADERS)/lwip/ipv6    \
                        -I$(SYSROOT_HEADERS)/espressif    \

where SYSROOT_HEADERS may be obtained this way:

SYSROOT = $(shell $(CC) --print-sysroot)
SYSROOT_HEADERS = $(SYSROOT)/usr/include

The project is updated from time to time, to get updates and prepare to build a new SDK, run:

$ make clean
$ git pull
$ git submodule sync
$ git submodule update

If you don't issue make clean (which causes toolchain and SDK to be rebuilt from scratch on next make), you risk getting broken/inconsistent results.

You can build a statically linked toolchain by uncommenting CT_STATIC_TOOLCHAIN=y in the file crosstool-config-overrides. More fine-tunable options may be available in that file and/or Makefile.

esp-open-sdk is in its nature merely a makefile, and is in public domain. However, the toolchain this makefile builds consists of many components, each having its own license. You should study and abide them all.

Quick summary: gcc is under GPL, which means that if you're distributing a toolchain binary you must be ready to provide complete toolchain sources on the first request.

Vendor SDK comes under modified MIT license. Newlib, used as C library comes with variety of BSD-like licenses. libgcc, compiler support library, comes with a linking exception. All the above means that for applications compiled with this toolchain, there are no specific requirements regarding source availability of the application or toolchain. (In other words, you can use it to build closed-source applications). (There're however standard attribution requirements - see licences for details).