526 lines
23 KiB
ReStructuredText
526 lines
23 KiB
ReStructuredText
===============
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Espressif ESP32
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===============
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The ESP32 is a series of single and dual-core SoCs from Espressif
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based on Harvard architecture Xtensa LX6 CPUs and with on-chip support
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for Bluetooth and Wi-Fi.
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All embedded memory, external memory and peripherals are located on the
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data bus and/or the instruction bus of these CPUs. With some minor
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exceptions, the address mapping of two CPUs is symmetric, meaning they
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use the same addresses to access the same memory. Multiple peripherals in
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the system can access embedded memory via DMA.
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On dual-core SoCs, the two CPUs are typically named "PRO_CPU" and "APP_CPU"
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(for "protocol" and "application"), however for most purposes the
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two CPUs are interchangeable.
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Toolchain
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=========
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You can use the prebuilt `toolchain <https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/tools/idf-tools.html#xtensa-esp32-elf>`__
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for Xtensa architecture and `OpenOCD <https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/tools/idf-tools.html#openocd-esp32>`__
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for ESP32 by Espressif.
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For flashing firmware, you will need to install ``esptool.py`` by running::
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$ pip install esptool
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Building from source
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--------------------
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You can also build the toolchain yourself. The steps to
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build the toolchain with crosstool-NG on Linux are as follows
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.. code-block:: console
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$ git clone https://github.com/espressif/crosstool-NG.git
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$ cd crosstool-NG
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$ git checkout esp-2021r1
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$ git submodule update --init
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$ ./bootstrap && ./configure --enable-local && make
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$ ./ct-ng xtensa-esp32-elf
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$ ./ct-ng build
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$ chmod -R u+w builds/xtensa-esp32-elf
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$ export PATH="crosstool-NG/builds/xtensa-esp32-elf/bin:$PATH"
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These steps are given in the setup guide in
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`ESP-IDF documentation <https://docs.espressif.com/projects/esp-idf/en/latest/get-started/linux-setup-scratch.html>`_.
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Flashing
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========
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Firmware for ESP32 is flashed via the USB/UART interface using the ``esptool.py`` tool.
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It's a two step process where the first converts the ELF file into a ESP32-compatible binary
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and the second flashes it to the board. These steps are included into the build system and you can
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flash your NuttX firmware simply by running::
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$ make flash ESPTOOL_PORT=<port>
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where ``<port>`` is typically ``/dev/ttyUSB0`` or similar. You can change the baudrate by passing ``ESPTOOL_BAUD``.
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Bootloader and partitions
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-------------------------
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ESP32 requires a bootloader to be flashed as well as a set of FLASH partitions. This is only needed the first time
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(or any time you which to modify either of these). An easy way is to use prebuilt binaries for NuttX `from here <https://github.com/espressif/esp-nuttx-bootloader>`__. In there you will find instructions to rebuild these if necessary.
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Once you downloaded both binaries, you can flash them by adding an ``ESPTOOL_BINDIR`` parameter, pointing to the directory where these binaries were downloaded:
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.. code-block:: console
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$ make flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=<dir>
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.. note:: It is recommended that if this is the first time you are using the board with NuttX that you perform a complete
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SPI FLASH erase.
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.. code-block:: console
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$ esptool.py erase_flash
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Peripheral Support
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==================
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The following list indicates the state of peripherals' support in NuttX:
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========== ======= =====
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Peripheral Support NOTES
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========== ======= =====
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GPIO Yes
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UART Yes
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SPI Yes
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I2C Yes
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DMA Yes
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Wifi Yes
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Ethernet Yes
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SPIFLASH Yes
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SPIRAM Yes
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Timers Yes
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Watchdog Yes
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RTC Yes
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RNG Yes
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AES Yes
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eFuse Yes
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ADC No
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Bluetooth Yes
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SDIO No
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SD/MMC No
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I2S Yes
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LED_PWM Yes
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RMT No
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MCPWM No
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Pulse_CNT No
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SHA No
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RSA No
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CAN/TWAI Yes
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========== ======= =====
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Memory Map
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==========
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Address Mapping
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---------------
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================== ========== ========== =============== ===============
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BUS TYPE START LAST DESCRIPTION NOTES
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================== ========== ========== =============== ===============
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0x00000000 0x3F3FFFFF Reserved
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Data 0x3F400000 0x3F7FFFFF External Memory
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Data 0x3F800000 0x3FBFFFFF External Memory
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0x3FC00000 0x3FEFFFFF Reserved
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Data 0x3FF00000 0x3FF7FFFF Peripheral
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Data 0x3FF80000 0x3FFFFFFF Embedded Memory
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Instruction 0x40000000 0x400C1FFF Embedded Memory
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Instruction 0x400C2000 0x40BFFFFF External Memory
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. 0x40C00000 0x4FFFFFFF Reserved
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Data / Instruction 0x50000000 0x50001FFF Embedded Memory
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. 0x50002000 0xFFFFFFFF Reserved
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================== ========== ========== =============== ===============
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Embedded Memory
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---------------
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=========== ========== ========== =============== ===============
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BUS TYPE START LAST DESCRIPTION NOTES
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=========== ========== ========== =============== ===============
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Data 0x3ff80000 0x3ff81fff RTC FAST Memory PRO_CPU Only
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. 0x3ff82000 0x3ff8ffff Reserved
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Data 0x3ff90000 0x3ff9ffff Internal ROM 1
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. 0x3ffa0000 0x3ffadfff Reserved
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Data 0x3ffae000 0x3ffdffff Internal SRAM 2 DMA
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Data 0x3ffe0000 0x3fffffff Internal SRAM 1 DMA
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=========== ========== ========== =============== ===============
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Boundary Address (Embedded)
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---------------------------
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====================== ========== ========== =============== ===============
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BUS TYPE START LAST DESCRIPTION NOTES
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====================== ========== ========== =============== ===============
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Instruction 0x40000000 0x40007fff Internal ROM 0 Remap
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Instruction 0x40008000 0x4005ffff Internal ROM 0
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. 0x40060000 0x4006ffff Reserved
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Instruction 0x40070000 0x4007ffff Internal SRAM 0 Cache
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Instruction 0x40080000 0x4009ffff Internal SRAM 0
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Instruction 0x400a0000 0x400affff Internal SRAM 1
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Instruction 0x400b0000 0x400b7FFF Internal SRAM 1 Remap
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Instruction 0x400b8000 0x400bffff Internal SRAM 1
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Instruction 0x400c0000 0x400c1FFF RTC FAST Memory PRO_CPU Only
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Data / Instruction 0x50000000 0x50001fff RTC SLOW Memory
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====================== ========== ========== =============== ===============
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External Memory
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---------------
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=========== ========== ========== =============== ===============
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BUS TYPE START LAST DESCRIPTION NOTES
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=========== ========== ========== =============== ===============
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Data 0x3f400000 0x3f7fffff External Flash Read
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Data 0x3f800000 0x3fbfffff External SRAM Read and Write
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=========== ========== ========== =============== ===============
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Boundary Address (External)
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---------------------------
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Instruction 0x400c2000 0x40bfffff 11512 KB External Flash Read
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Linker Segments
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---------------
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+---------------------+------------+------------+------+------------------------------+
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| DESCRIPTION | START | END | ATTR | LINKER SEGMENT NAME |
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+=====================+============+============+======+==============================+
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| FLASH mapped data: | 0x3f400010 | 0x3fc00010 | R | drom0_0_seg |
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| - .rodata | | | | |
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| - Constructors | | | | |
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| /destructors | | | | |
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+---------------------+------------+------------+------+------------------------------+
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| COMMON data RAM: | 0x3ffb0000 | 0x40000000 | RW | dram0_0_seg (NOTE 1,2,3) |
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| - .bss/.data | | | | |
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+---------------------+------------+------------+------+------------------------------+
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| IRAM for PRO cpu: | 0x40080000 | 0x400a0000 | RX | iram0_0_seg |
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| - Interrupt Vectors| | | | |
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| - Low level | | | | |
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| handlers | | | | |
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| - Xtensa/Espressif | | | | |
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| libraries | | | | |
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+---------------------+------------+------------+------+------------------------------+
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| RTC fast memory: | 0x400c0000 | 0x400c2000 | RWX | rtc_iram_seg (PRO_CPU only) |
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| - .rtc.text | | | | |
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| (unused?) | | | | |
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+---------------------+------------+------------+------+------------------------------+
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| FLASH: | 0x400d0018 | 0x40400018 | RX | iram0_2_seg (actually FLASH)|
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| - .text | | | | |
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+---------------------+------------+------------+------+------------------------------+
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| RTC slow memory: | 0x50000000 | 0x50001000 | RW | rtc_slow_seg (NOTE 4) |
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| - .rtc.data/rodata | | | | |
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| (unused?) | | | | |
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+---------------------+------------+------------+------+------------------------------+
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.. note::
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(1) Linker script will reserve space at the beginning of the segment
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for BT and at the end for trace memory.
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(2) Heap ends at the top of dram_0_seg.
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(3) Parts of this region is reserved for the ROM bootloader.
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(4) Linker script will reserve space at the beginning of the segment
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for co-processor reserve memory and at the end for ULP coprocessor
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reserve memory.
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64-bit Timers
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=============
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ESP32 has 4 generic timers of 64 bits (2 from Group 0 and 2 from Group 1). They're
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accessible as character drivers, the configuration along with a guidance on how
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to run the example and the description of the application level interface
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can be found :doc:`here </components/drivers/character/timer>`.
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Watchdog Timers
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===============
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ESP32 has 3 WDTs. 2 MWDTS from the Timers Module and 1 RWDT from the RTC Module
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(Currently not supported yet). They're accessible as character drivers,
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The configuration along with a guidance on how to run the example and the description
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of the application level interface can be found
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:doc:`here </components/drivers/character/watchdog>`.
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SMP
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===
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The ESP32 has 2 CPUs. Support is included for testing an SMP configuration.
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That configuration is still not yet ready for usage but can be enabled with
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the following configuration settings,
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in :menuselection:`RTOS Features --> Tasks and Scheduling`, with::
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CONFIG_SPINLOCK=y
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CONFIG_SMP=y
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CONFIG_SMP_NCPUS=2
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Debug Tip: During debug session, OpenOCD may mysteriously switch from one
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CPU to another. This behavior can be eliminated by uncommenting one of the
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following in ``scripts/esp32.cfg``::
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# Only configure the PRO CPU
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#set ESP32_ONLYCPU 1
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# Only configure the APP CPU
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#set ESP32_ONLYCPU 2
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Wi-Fi
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=====
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A standard network interface will be configured and can be initialized such as::
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nsh> ifup wlan0
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nsh> wapi psk wlan0 mypasswd 3
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nsh> wapi essid wlan0 myssid 1
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nsh> renew wlan0
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In this case a connection to AP with SSID ``myssid`` is done, using ``mypasswd`` as
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password. IP address is obtained via DHCP using ``renew`` command. You can check
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the result by running ``ifconfig`` afterwards.
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.. tip:: Boards usually expose a ``wapi`` defconfig which enables Wi-Fi
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Wi-Fi SoftAP
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============
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It is possible to use ESP32 as an Access Point (SoftAP). Actually there are some
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boards config examples called sta_softap which enables this support
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If you are using this board config profile you can run these commands to be able
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to connect your smartphone or laptop to your board::
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nsh> ifup wlan1
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nsh> dhcpd_start wlan1
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nsh> wapi psk wlan1 mypasswd 3
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nsh> wapi essid wlan1 nuttxap 1
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In this case, you are creating the access point ``nuttxapp`` in your board and to
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connect to it on your smartphone you will be required to type the password ``mypasswd``
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using WPA2.
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The ``dhcpd_start`` is necessary to let your board to associate an IP to your smartphone.
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Bluetooth
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=========
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These are the steps to test Bluetooth Low Energy (BLE) scan on ESP32 (i.e. Devkit board).
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First configure to use the BLE board profile::
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$ make distclean
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$ ./tools/configure.sh esp32-devkitc:ble
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$ make flash ESPTOOL_PORT=/dev/ttyUSB0
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Enter in the NSH shell using your preferred serial console tool and run the scan command::
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NuttShell (NSH) NuttX-10.2.0
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nsh> ifconfig
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bnep0 Link encap:UNSPEC at DOWN
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inet addr:0.0.0.0 DRaddr:0.0.0.0 Mask:0.0.0.0
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wlan0 Link encap:Ethernet HWaddr ac:67:b2:53:8b:ec at UP
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inet addr:10.0.0.2 DRaddr:10.0.0.1 Mask:255.255.255.0
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nsh> bt bnep0 scan start
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nsh> bt bnep0 scan stop
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nsh> bt bnep0 scan get
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Scan result:
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1. addr: 63:14:2f:b9:9f:83 type: 1
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rssi: -90
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response type: 3
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advertiser data: 1e ff 06 00 01 09 20 02 7c 33 a3 a7 cd c9 44 5b
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2. addr: 52:ca:05:b5:ad:77 type: 1
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rssi: -82
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response type: 3
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advertiser data: 1e ff 06 00 01 09 20 02 03 d1 21 57 bf 19 b3 7a
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3. addr: 46:8e:b2:cd:94:27 type: 1
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rssi: -92
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response type: 2
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advertiser data: 02 01 1a 09 ff c4 00 10 33 14 12 16 80 02 0a d4
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4. addr: 46:8e:b2:cd:94:27 type: 1
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rssi: -92
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response type: 4
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advertiser data: 18 09 5b 4c 47 5d 20 77 65 62 4f 53 20 54 56 20
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5. addr: 63:14:2f:b9:9f:83 type: 1
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rssi: -80
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response type: 3
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advertiser data: 1e ff 06 00 01 09 20 02 7c 33 a3 a7 cd c9 44 5b
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nsh>
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I2S
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===
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The I2S peripheral is accessible using either the generic I2S audio driver or a specific
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audio codec driver. Also, it's possible to use the I2S character driver to bypass the
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audio subsystem and develop specific usages of the I2S peripheral.
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.. note:: Note that the bit-width and sample rate can be modified "on-the-go" when using
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audio-related drivers. That is not the case for the I2S character device driver and
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such parameters are set on compile time through `make menuconfig`.
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Please check for usage examples using the :doc:`ESP32 DevKitC </platforms/xtensa/esp32/boards/esp32-devkitc/index>`.
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Using QEMU
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==========
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First follow the instructions `here <https://github.com/espressif/qemu/wiki>`__ to build QEMU.
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Enable the ``ESP32_QEMU_IMAGE`` config found in :menuselection:`Board Selection --> ESP32 binary image for QEMU`.
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Download the bootloader and the partition table from https://github.com/espressif/esp-nuttx-bootloader/releases
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and place them in a directory, say ``../esp-bins``.
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Build and generate the QEMU image::
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$ make ESPTOOL_BINDIR=../esp-bins
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A QEMU-compatible ``nuttx.merged.bin`` binary image will be created. It can be run as::
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$ qemu-system-xtensa -nographic -machine esp32 -drive file=nuttx.merged.bin,if=mtd,format=raw
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Secure Boot and Flash Encryption
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================================
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Secure Boot
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-----------
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Secure Boot protects a device from running any unauthorized (i.e., unsigned) code by checking that
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each piece of software that is being booted is signed. On an ESP32, these pieces of software include
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the second stage bootloader and each application binary. Note that the first stage bootloader does not
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require signing as it is ROM code thus cannot be changed. This is achieved using specific hardware in
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conjunction with MCUboot (read more about MCUboot `here <https://docs.mcuboot.com/>`__).
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The Secure Boot process on the ESP32 involves the following steps performed:
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1. The first stage bootloader verifies the second stage bootloader's RSA-PSS signature. If the verification is successful,
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the first stage bootloader loads and executes the second stage bootloader.
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2. When the second stage bootloader loads a particular application image, the application's signature (RSA, ECDSA or ED25519) is verified
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by MCUboot.
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If the verification is successful, the application image is executed.
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.. warning:: Once enabled, Secure Boot will not boot a modified bootloader. The bootloader will only boot an
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application firmware image if it has a verified digital signature. There are implications for reflashing
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updated images once Secure Boot is enabled. You can find more information about the ESP32's Secure boot
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`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32/security/secure-boot-v2.html>`__.
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.. note:: As the bootloader image is built on top of the Hardware Abstraction Layer component
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of `ESP-IDF <https://github.com/espressif/esp-idf>`_, the
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`API port by Espressif <https://docs.mcuboot.com/readme-espressif.html>`_ will be used
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by MCUboot rather than the original NuttX port.
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Flash Encryption
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----------------
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Flash encryption is intended for encrypting the contents of the ESP32's off-chip flash memory. Once this feature is enabled,
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firmware is flashed as plaintext, and then the data is encrypted in place on the first boot. As a result, physical readout
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of flash will not be sufficient to recover most flash contents.
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.. warning:: After enabling Flash Encryption, an encryption key is generated internally by the device and
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cannot be accessed by the user for re-encrypting data and re-flashing the system, hence it will be permanently encrypted.
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Re-flashing an encrypted system is complicated and not always possible. You can find more information about the ESP32's Flash Encryption
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`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32/security/flash-encryption.html>`__.
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Prerequisites
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-------------
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First of all, we need to install ``imgtool`` (a MCUboot utility application to manipulate binary
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images) and ``esptool`` (the ESP32 toolkit)::
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$ pip install imgtool esptool
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We also need to make sure that the python modules are added to ``PATH``::
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$ echo "PATH=$PATH:/home/$USER/.local/bin" >> ~/.bashrc
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Now, we will create a folder to store the generated keys (such as ``~/signing_keys``)::
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$ mkdir ~/signing_keys && cd ~/signing_keys
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With all set up, we can now generate keys to sign the bootloader and application binary images,
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respectively, of the compiled project::
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$ espsecure.py generate_signing_key --version 2 bootloader_signing_key.pem
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$ imgtool keygen --key app_signing_key.pem --type rsa-3072
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.. important:: The contents of the key files must be stored securely and kept secret.
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Enabling Secure Boot and Flash Encryption
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-----------------------------------------
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To enable Secure Boot for the current project, go to the project's NuttX directory, execute ``make menuconfig`` and the following steps:
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1. Enable experimental features in :menuselection:`Build Setup --> Show experimental options`;
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2. Enable MCUboot in :menuselection:`Application Configuration --> Bootloader Utilities --> MCUboot`;
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3. Change image type to ``MCUboot-bootable format`` in :menuselection:`System Type --> Application Image Configuration --> Application Image Format`;
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4. Enable building MCUboot from the source code by selecting ``Build binaries from source``;
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in :menuselection:`System Type --> Application Image Configuration --> Source for bootloader binaries`;
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5. Enable Secure Boot in :menuselection:`System Type --> Application Image Configuration --> Enable hardware Secure Boot in bootloader`;
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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 <https://docs.mcuboot.com/design.html>`_ and the
|
|
`MCUboot Espressif port documentation <https://docs.mcuboot.com/readme-espressif.html>`_ for
|
|
more information on how to apply MCUboot. Also check some `notes about the NuttX MCUboot port <https://github.com/mcu-tools/mcuboot/blob/main/docs/readme-nuttx.md>`_,
|
|
the `MCUboot porting guide <https://github.com/mcu-tools/mcuboot/blob/main/docs/PORTING.md>`_ and some
|
|
`examples of MCUboot applied in Nuttx applications <https://github.com/apache/nuttx-apps/tree/master/examples/mcuboot>`_.
|
|
|
|
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 <https://docs.mcuboot.com/design.html#image-swapping>`_).
|
|
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.**
|
|
|
|
|
|
Things to Do
|
|
============
|
|
|
|
1. Lazy co-processor save logic supported by Xtensa. That logic works like this:
|
|
|
|
a. CPENABLE is set to zero on each context switch, disabling all co-
|
|
processors.
|
|
b. If/when the task attempts to use the disabled co-processor, an
|
|
exception occurs
|
|
c. The co-processor exception handler re-enables the co-processor.
|
|
|
|
Instead, the NuttX logic saves and restores CPENABLE on each context
|
|
switch. This has disadvantages in that (1) co-processor context will
|
|
be saved and restored even if the co-processor was never used, and (2)
|
|
tasks must explicitly enable and disable co-processors.
|
|
|
|
2. Currently the Xtensa port copies register state save information from
|
|
the stack into the TCB. A more efficient alternative would be to just
|
|
save a pointer to a register state save area in the TCB. This would
|
|
add some complexity to signal handling and also to up_initialstate().
|
|
But the performance improvement might be worth the effort.
|
|
|
|
3. See SMP-related issues above
|
|
|
|
Supported Boards
|
|
================
|
|
|
|
.. toctree::
|
|
:glob:
|
|
:maxdepth: 1
|
|
|
|
boards/*/*
|