================== Espressif ESP32-S2 ================== The ESP32-S2 is a series of single-core SoCs from Espressif based on Harvard architecture Xtensa LX7 CPU and with on-chip support for Wi-Fi. All embedded memory, external memory and peripherals are located on the data bus and/or the instruction bus of the CPU. Multiple peripherals in the system can access embedded memory via DMA. Toolchain ========= You can use the prebuilt `toolchain `__ for Xtensa architecture and `OpenOCD `__ for ESP32-S2 by Espressif. For flashing firmware, you will need to install ``esptool.py`` by running:: $ pip install esptool Building from source -------------------- You can also build the toolchain yourself. The steps to build the toolchain with crosstool-NG on Linux are as follows .. code-block:: console $ git clone https://github.com/espressif/crosstool-NG.git $ cd crosstool-NG $ git checkout esp-2021r1 $ git submodule update --init $ ./bootstrap && ./configure --enable-local && make $ ./ct-ng xtensa-esp32-elf $ ./ct-ng build $ chmod -R u+w builds/xtensa-esp32-elf $ export PATH="crosstool-NG/builds/xtensa-esp32-elf/bin:$PATH" Alternatively, you may follow the steps in `ESP-IDF documentation `_. Flashing ======== Firmware for ESP32-S2 is flashed via the USB/UART or internal USB DEVICE JTAG interface using the ``esptool.py`` tool. It's a two-step process where the first converts the ELF file into a ESP32-S2 compatible binary and the second flashes it to the board. These steps are included in the build system and you can flash your NuttX firmware simply by running:: $ make flash ESPTOOL_PORT= where ```` is typically ``/dev/ttyUSB0`` or similar. You can change the baudrate by passing ``ESPTOOL_BAUD``. Bootloader and partitions ------------------------- ESP32-S2 requires a bootloader to be flashed as well as a set of FLASH partitions. This is only needed the first time (or any time you which to modify either of these). An easy way is to use prebuilt binaries for NuttX `from here `__. In there you will find instructions to rebuild these if necessary. Once you downloaded both binaries, you can flash them by adding an ``ESPTOOL_BINDIR`` parameter, pointing to the directory where these binaries were downloaded: .. code-block:: console $ make flash ESPTOOL_PORT= ESPTOOL_BINDIR= .. note:: It is recommended that if this is the first time you are using the board with NuttX that you perform a complete SPI FLASH erase. .. code-block:: console $ esptool.py erase_flash .. note:: Alternatively, you can automatically download the bootloader/partitions from the NuttX build system by using the following command: .. code-block:: console $ make bootloader The binaries will be downloaded to the project's main folder and ``ESPTOOL_BINDIR`` may be set as ``.`` Peripheral Support ================== The following list indicates the state of peripherals' support in NuttX: ========== ======= ===== Peripheral Support NOTES ========== ======= ===== ADC No AES No CAN/TWAI Yes DMA Yes eFuse No Ethernet No GPIO Yes I2C Yes I2S Yes LED_PWM No Pulse_CNT No RMT No RNG Yes RSA No RTC Yes SHA No SPI Yes SPIFLASH Yes SPIRAM Yes Timers Yes Touch Yes UART Yes Watchdog Yes Wifi No ========== ======= ===== Memory Map ========== Address Mapping --------------- ================== ========== ========== =============== =============== BUS TYPE START LAST DESCRIPTION NOTES ================== ========== ========== =============== =============== . 0x00000000 0x3EFFFFFF Reserved Data 0x3F000000 0x3F3FFFFF External Memory Data 0x3F400000 0x3F4FFFFF Peripheral Data 0x3F500000 0x3FF7FFFF External Memory . 0x3FF80000 0x3FF9DFFF Reserved Data 0x3FF9E000 0x3FFFFFFF Embedded Memory Instruction 0x40000000 0x40071FFF Embedded Memory . 0x40072000 0x4007FFFF Reserved Instruction 0x40080000 0x407FFFFF External Memory . 0x40800000 0x4FFFFFFF Reserved Data / Instruction 0x50000000 0x50001FFF Embedded Memory . 0x50002000 0x5FFFFFFF Reserved Data / Instruction 0x60000000 0x600BFFFF Peripheral . 0x600C0000 0x617FFFFF Reserved Data / Instruction 0x61800000 0x61803FFF Peripheral . 0x61804000 0xFFFFFFFF Reserved ================== ========== ========== =============== =============== Embedded Memory --------------- =========== ========== ========== =============== ================== ===== BUS TYPE START LAST DESCRIPTION PERMISSION CONTROL NOTES =========== ========== ========== =============== ================== ===== Data 0x3FF9E000 0x3FF9FFFF RTC FAST Memory YES Data 0x3FFA0000 0x3FFAFFFF Internal ROM 1 NO Data 0x3FFB0000 0x3FFB7FFF Internal SRAM 0 YES DMA Data 0x3FFB8000 0x3FFFFFFF Internal SRAM 1 YES DMA =========== ========== ========== =============== ================== ===== Boundary Address (Embedded) --------------------------- ====================== ========== ========== =============== ================== =============== BUS TYPE START LAST DESCRIPTION PERMISSION CONTROL NOTES ====================== ========== ========== =============== ================== =============== Instruction 0x40000000 0x4000FFFF Internal ROM 0 NO Instruction 0x40010000 0x4001FFFF Internal ROM 1 NO Instruction 0x40020000 0x40027FFF Internal SRAM 0 YES Instruction 0x40028000 0x4006FFFF Internal SRAM 1 YES Instruction 0x40070000 0x40071FFF RTC FAST Memory YES Data / Instruction 0x50000000 0x50001FFF RTC SLOW Memory YES ====================== ========== ========== =============== ================== =============== External Memory --------------- =========== ========== ========== =============== ================== =============== BUS TYPE START LAST DESCRIPTION PERMISSION CONTROL NOTES =========== ========== ========== =============== ================== =============== Data 0x3F000000 0x3F3FFFFF ICache YES Read Data 0x3F500000 0x3FF7FFFF DCache YES Read and Write =========== ========== ========== =============== ================== =============== Boundary Address (External) --------------------------- =========== ========== ========== =============== ================== =============== BUS TYPE START LAST DESCRIPTION PERMISSION CONTROL NOTES =========== ========== ========== =============== ================== =============== Instruction 0x40080000 0x407FFFFF ICache YES Read =========== ========== ========== =============== ================== =============== Linker Segments --------------- +---------------------+------------+-------------------+------+------------------------------+ | DESCRIPTION | START | END | ATTR | LINKER SEGMENT NAME | +=====================+============+===================+======+==============================+ | FLASH mapped data: | 0X3F000020 | 0X3F000020 + | R | drom0_0_seg (NOTE 1) | | - .rodata | | FLASH_SIZE - 0x20 | | | | - Constructors | | | | | | /destructors | | | | | +---------------------+------------+-------------------+------+------------------------------+ | COMMON data RAM: | 0X3FFB0000 | 0x3FFDE000 | RW | dram0_0_seg (NOTE 2) | | - .bss/.data | | | | | +---------------------+------------+-------------------+------+------------------------------+ | IRAM for PRO cpu: | 0x40022000 | 0x40050000 | RX | iram0_0_seg | | - Interrupt Vectors| | | | | | - Low level | | | | | | handlers | | | | | | - Xtensa/Espressif | | | | | | libraries | | | | | +---------------------+------------+-------------------+------+------------------------------+ | RTC fast memory: | 0x40070000 | 0x40072000 | RWX | rtc_iram_seg | | - .rtc.text | | | | | | (unused?) | | | | | +---------------------+------------+-------------------+------+------------------------------+ | FLASH: | 0x40080020 | 0x40080020 + | RX | irom0_0_seg (actually FLASH) | | - .text | | FLASH_SIZE | | | | | | (NOTE 3) | | | +---------------------+------------+-------------------+------+------------------------------+ | RTC slow memory: | 0x50000000 | 0x50002000 | RW | rtc_slow_seg (NOTE 4) | | - .rtc.data/rodata | | | | | | (unused?) | | | | | +---------------------+------------+-------------------+------+------------------------------+ .. note:: (1) The linker script will reserve space at the beginning of the segment for MCUboot header if ESP32S2_APP_FORMAT_MCUBOOT flag is active. (2) Heap starts at the end of dram_0_seg. (3) Subtract 0x20 if ESP32S2_APP_FORMAT_MCUBOOT is not active. (4) Linker script will reserve space at the beginning and at the end of the segment for ULP coprocessor reserve memory. 64-bit Timers ============= ESP32-S2 has 4 generic timers of 64 bits (2 from Group 0 and 2 from Group 1). They're accessible as character drivers, the configuration along with a guidance on how to run the example and the description of the application level interface can be found in the :doc:`timer documentation `. Watchdog Timers =============== ESP32-S2 has 3 WDTs. 2 MWDTs from the Timers Module and 1 RWDT from the RTC Module (Currently not supported yet). They're accessible as character drivers, The configuration along with a guidance on how to run the example and the description of the application level interface can be found in the :doc:`watchdog documentation `. I2S === The I2S peripheral is accessible using either the generic I2S audio driver or a specific audio codec driver. Also, it's possible to use the I2S character driver to bypass the audio subsystem and develop specific usages of the I2S peripheral. .. note:: Note that the bit-width and sample rate can be modified "on-the-go" when using audio-related drivers. That is not the case for the I2S character device driver and such parameters are set on compile time through `make menuconfig`. Please check for usage examples using the :doc:`ESP32-S2-Saola-1 `. Secure Boot and Flash Encryption ================================ Secure Boot ----------- Secure Boot protects a device from running any unauthorized (i.e., unsigned) code by checking that each piece of software that is being booted is signed. On an ESP32-S2, these pieces of software include the second stage bootloader and each application binary. Note that the first stage bootloader does not require signing as it is ROM code thus cannot be changed. This is achieved using specific hardware in conjunction with MCUboot (read more about MCUboot `here `__). The Secure Boot process on the ESP32-S2 involves the following steps performed: 1. The first stage bootloader verifies the second stage bootloader's RSA-PSS signature. If the verification is successful, the first stage bootloader loads and executes the second stage bootloader. 2. When the second stage bootloader loads a particular application image, the application's signature (RSA, ECDSA or ED25519) is verified by MCUboot. If the verification is successful, the application image is executed. .. warning:: Once enabled, Secure Boot will not boot a modified bootloader. The bootloader will only boot an application firmware image if it has a verified digital signature. There are implications for reflashing updated images once Secure Boot is enabled. You can find more information about the ESP32-S2's Secure boot `here `__. .. note:: As the bootloader image is built on top of the Hardware Abstraction Layer component of `ESP-IDF `_, the `API port by Espressif `_ will be used by MCUboot rather than the original NuttX port. Flash Encryption ---------------- Flash encryption is intended for encrypting the contents of the ESP32-S2's off-chip flash memory. Once this feature is enabled, firmware is flashed as plaintext, and then the data is encrypted in place on the first boot. As a result, physical readout of flash will not be sufficient to recover most flash contents. .. warning:: After enabling Flash Encryption, an encryption key is generated internally by the device and cannot be accessed by the user for re-encrypting data and re-flashing the system, hence it will be permanently encrypted. Re-flashing an encrypted system is complicated and not always possible. You can find more information about the ESP32-S2's Flash Encryption `here `__. Prerequisites ------------- First of all, we need to install ``imgtool`` (a MCUboot utility application to manipulate binary images) and ``esptool`` (the ESP32-S2 toolkit):: $ pip install imgtool esptool We also need to make sure that the python modules are added to ``PATH``:: $ echo "PATH=$PATH:/home/$USER/.local/bin" >> ~/.bashrc Now, we will create a folder to store the generated keys (such as ``~/signing_keys``):: $ mkdir ~/signing_keys && cd ~/signing_keys With all set up, we can now generate keys to sign the bootloader and application binary images, respectively, of the compiled project:: $ espsecure.py generate_signing_key --version 2 bootloader_signing_key.pem $ imgtool keygen --key app_signing_key.pem --type rsa-3072 .. important:: The contents of the key files must be stored securely and kept secret. Enabling Secure Boot and Flash Encryption ----------------------------------------- To enable Secure Boot for the current project, go to the project's NuttX directory, execute ``make menuconfig`` and the following steps: 1. Enable experimental features in :menuselection:`Build Setup --> Show experimental options`; 2. Enable MCUboot in :menuselection:`Application Configuration --> Bootloader Utilities --> MCUboot`; 3. Change image type to ``MCUboot-bootable format`` in :menuselection:`System Type --> Application Image Configuration --> Application Image Format`; 4. Enable building MCUboot from the source code by selecting ``Build binaries from source``; in :menuselection:`System Type --> Application Image Configuration --> Source for bootloader binaries`; 5. Enable Secure Boot in :menuselection:`System Type --> Application Image Configuration --> Enable hardware Secure Boot in bootloader`; 6. If you want to protect the SPI Bus against data sniffing, you can enable Flash Encryption in :menuselection:`System Type --> Application Image Configuration --> Enable Flash Encryption on boot`. Now you can design an update and confirm agent to your application. Check the `MCUboot design guide `_ and the `MCUboot Espressif port documentation `_ for more information on how to apply MCUboot. Also check some `notes about the NuttX MCUboot port `_, the `MCUboot porting guide `_ and some `examples of MCUboot applied in Nuttx applications `_. After you developed an application which implements all desired functions, you need to flash it into the primary image slot of the device (it will automatically be in the confirmed state, you can learn more about image confirmation `here `__). To flash to the primary image slot, select ``Application image primary slot`` in :menuselection:`System Type --> Application Image Configuration --> Target slot for image flashing` and compile it using ``make -j ESPSEC_KEYDIR=~/signing_keys``. When creating update images, make sure to change :menuselection:`System Type --> Application Image Configuration --> Target slot for image flashing` to ``Application image secondary slot``. .. important:: When deploying your application, make sure to disable UART Download Mode by selecting ``Permanently disabled`` in :menuselection:`System Type --> Application Image Configuration --> UART ROM download mode` and change usage mode to ``Release`` in `System Type --> Application Image Configuration --> Enable usage mode`. **After disabling UART Download Mode you will not be able to flash other images through UART.** Supported Boards ================ .. toctree:: :glob: :maxdepth: 1 boards/*/*