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Eren Terzioglu 328ffdb297 Docs/platforms/espressif: Add UF2 file format docs 
Add UF2 file format docs for RISC-V based Espressif devices

Signed-off-by: Eren Terzioglu <eren.terzioglu@espressif.com>
2026-05-27 14:29:35 -04:00

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==================
Espressif ESP32-C6
==================
The ESP32-C6 is an ultra-low-power and highly integrated SoC with a RISC-V
core and supports 2.4 GHz Wi-Fi 6, Bluetooth 5 (LE) and the 802.15.4 protocol.
* Address Space
- 800 KB of internal memory address space accessed from the instruction bus
- 560 KB of internal memory address space accessed from the data bus
- 1016 KB of peripheral address space
- 8 MB of external memory virtual address space accessed from the instruction bus
- 8 MB of external memory virtual address space accessed from the data bus
- 480 KB of internal DMA address space
* Internal Memory
- 320 KB ROM
- 512 KB SRAM (16 KB can be configured as Cache)
- 16 KB of SRAM in RTC
* External Memory
- Up to 16 MB of external flash
* Peripherals
- 35 peripherals
* GDMA
- 7 modules are capable of DMA operations.
ESP32-C6 Toolchain
==================
A generic RISC-V toolchain can be used to build ESP32-C6 projects. It's recommended to use the same
toolchain used by NuttX CI. Please refer to the Docker
`container <https://github.com/apache/nuttx/tree/master/tools/ci/docker/linux/Dockerfile>`_ and
check for the current compiler version being used. For instance:
.. code-block::
###############################################################################
# Build image for tool required by RISCV builds
###############################################################################
FROM nuttx-toolchain-base AS nuttx-toolchain-riscv
# Download the latest RISCV GCC toolchain prebuilt by xPack
RUN mkdir riscv-none-elf-gcc && \
curl -s -L "https://github.com/xpack-dev-tools/riscv-none-elf-gcc-xpack/releases/download/v13.2.0-2/xpack-riscv-none-elf-gcc-13.2.0-2-linux-x64.tar.gz" \
| tar -C riscv-none-elf-gcc --strip-components 1 -xz
It uses the xPack's prebuilt toolchain based on GCC 13.2.0-2.
Installing
----------
First, create a directory to hold the toolchain:
.. code-block:: console
$ mkdir -p /path/to/your/toolchain/riscv-none-elf-gcc
Download and extract toolchain:
.. code-block:: console
$ curl -s -L "https://github.com/xpack-dev-tools/riscv-none-elf-gcc-xpack/releases/download/v13.2.0-2/xpack-riscv-none-elf-gcc-13.2.0-2-linux-x64.tar.gz" \
| tar -C /path/to/your/toolchain/riscv-none-elf-gcc --strip-components 1 -xz
Add the toolchain to your `PATH`:
.. code-block:: console
$ echo "export PATH=/path/to/your/toolchain/riscv-none-elf-gcc/bin:$PATH" >> ~/.bashrc
You can edit your shell's rc files if you don't use bash.
Building and flashing NuttX
===========================
Installing esptool
------------------
First, make sure that ``esptool.py`` is installed and up-to-date.
This tool is used to convert the ELF to a compatible ESP32-C6 image and to flash the image into the board.
It can be installed with: ``pip install esptool>=4.8.1``.
.. warning::
Installing ``esptool.py`` may required a Python virtual environment on newer systems.
This will be the case if the ``pip install`` command throws an error such as:
``error: externally-managed-environment``.
If you are not familiar with virtual environments, refer to `Managing esptool on virtual environment`_ for instructions on how to install ``esptool.py``.
Bootloader and partitions
-------------------------
NuttX can boot the ESP32-C6 directly using the so-called "Simple Boot".
An externally-built 2nd stage bootloader is not required in this case as all
functions required to boot the device are built within NuttX. Simple boot does not
require any specific configuration (it is selectable by default if no other
2nd stage bootloader is used). For compatibility among other SoCs and future options
of 2nd stage bootloaders, the commands ``make bootloader`` and the ``ESPTOOL_BINDIR``
option (for the ``make flash``) are kept (and ignored if Simple Boot is used).
If features like `Flash Encryption`_ are required, an externally-built 2nd stage bootloader is needed.
The MCUBoot bootloader is built using the ``make bootloader`` command. This command generates
the firmware in the ``nuttx`` folder. The ``ESPTOOL_BINDIR`` is used in the
``make flash`` command to specify the path to the bootloader. For compatibility
among other SoCs and future options of 2nd stage bootloaders, the commands
``make bootloader`` and the ``ESPTOOL_BINDIR`` option (for the ``make flash``)
can be used even if no externally-built 2nd stage bootloader
is being built (they will be ignored if Simple Boot is used, for instance)::
$ make bootloader
.. note:: It is recommended that if this is the first time you are using the board with NuttX to
perform a complete SPI FLASH erase.
.. code-block:: console
$ esptool.py erase_flash
Building and Flashing
---------------------
This is a two-step process where the first step converts the ELF file into an ESP32-C6 compatible binary
and the second step flashes it to the board. These steps are included in the build system and it is
possible to build and flash the NuttX firmware simply by running::
$ make flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=./
where:
* ``ESPTOOL_PORT`` is typically ``/dev/ttyUSB0`` or similar.
* ``ESPTOOL_BINDIR=./`` is the path of the externally-built 2nd stage bootloader and the partition table (if applicable): when built using the ``make bootloader``, these files are placed into ``nuttx`` folder.
* ``ESPTOOL_BAUD`` is able to change the flash baud rate if desired.
To create and flash with UF2 (USB Flashing Format) binary, ``UF2=1`` option needs to be set during build phase
(e.g ``make UF2=1 -j8``). This flag will create UF2 format file addition to binary. This output can be used to
flash the device with `ESP USB Bridge <https://github.com/espressif/esp-usb-bridge>`__.
To flash using ESP USB Bridge, either drag and drop the generated UF2 file onto the flasher's
mass storage device, or use the ``UF2=1`` flag during flashing (e.g. ``make flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=./ UF2=1``)
Flashing NSH Example
--------------------
This example shows how to build and flash the ``nsh`` defconfig for the ESP32-C6-DevKitC-1 board::
$ cd nuttx
$ make distclean
$ ./tools/configure.sh esp32c6-devkitc:nsh
$ make -j$(nproc)
When the build is complete, the firmware can be flashed to the board using the command::
$ make -j$(nproc) flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=./
where ``<port>`` is the serial port where the board is connected::
$ make flash ESPTOOL_PORT=/dev/ttyUSB0 ESPTOOL_BINDIR=./
CP: nuttx.hex
MKIMAGE: NuttX binary
esptool.py -c esp32c6 elf2image --ram-only-header -fs 4MB -fm dio -ff 80m -o nuttx.bin nuttx
esptool.py v4.8.1
Creating esp32c6 image...
Image has only RAM segments visible. ROM segments are hidden and SHA256 digest is not appended.
Merged 1 ELF section
Successfully created esp32c6 image.
Generated: nuttx.bin
esptool.py -c esp32c6 -p /dev/ttyUSB0 -b 921600 write_flash -fs 4MB -fm dio -ff 80m 0x0000 nuttx.bin
esptool.py v4.8.1
Serial port /dev/ttyUSB0
Connecting....
Chip is ESP32-C6 (QFN40) (revision v0.0)
[...]
Flash will be erased from 0x00000000 to 0x0003cfff...
Compressed 248628 bytes to 106757...
Wrote 248628 bytes (106757 compressed) at 0x00000000 in 2.5 seconds (effective 805.6 kbit/s)...
Hash of data verified.
Leaving...
Hard resetting via RTS pin...
Now opening the serial port with a terminal emulator should show the NuttX console::
$ picocom -b 115200 /dev/ttyUSB0
NuttShell (NSH) NuttX-12.8.0
nsh> uname -a
NuttX 12.8.0 759d37b97c-dirty Mar 5 2025 19:42:41 risc-v esp32c6-devkitc
Building with CMake
-------------------
General CMake usage (out-of-tree build, ``menuconfig`` target, and so on) is described in
:doc:`/quickstart/compiling_cmake`. The ESP32-C6 common arch enables post-build steps that
produce ``nuttx.bin`` (and related images) under the **CMake binary directory**; the build
log also prints suggested ``esptool.py`` command lines for your layout.
Example (NuttX shell defconfig, Ninja generator)::
$ cd nuttx
$ cmake -B build -DBOARD_CONFIG=esp32c6-devkitc:nsh -GNinja
$ cmake --build build
To reconfigure the tree after changing options (same as other NuttX CMake boards)::
$ cmake --build build -t menuconfig
$ cmake --build build
Persistent HAL cache (``NXTMPDIR``)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Pass ``-DNXTMPDIR=ON`` at **configure** time to reuse a persistent clone of the
``esp-hal-3rdparty`` repository under ``nuttx/../nxtmpdir/esp-hal-3rdparty``. CMake checks
the expected revision; if it does not match, the cache directory is refreshed. This cuts
repeat configure/build time when the HAL checkout would otherwise be re-fetched into the
binary directory.
Example::
$ cmake -B build -DBOARD_CONFIG=esp32c6-devkitc:nsh -DNXTMPDIR=ON -GNinja
$ cmake --build build
MCUBoot: building the 2nd-stage bootloader (``-t bootloader``)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
For configurations that use MCUboot, build the bootloader the same way as
with Make, but via the CMake target::
$ cmake --build build -t bootloader
The image is installed as ``mcuboot-esp32c6.bin`` in the NuttX **source** directory (not
inside ``build/``).
.. note::
Flashing paths differ from the pure-Make flow: the application image is under your CMake
build directory (for example ``build/nuttx.bin``), while MCUboot binaries live next to
``nuttx`` sources. Use the ``esptool.py`` hints printed at the end of the build, or the
same offsets as documented for ``make flash`` with ``ESPTOOL_BINDIR``.
Target flashing (``-t flash``)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
After a successful CMake build, you can flash the chip with the ``flash`` custom target.
This is the CMake-side equivalent of the Make ``FLASH`` logic in
``tools/espressif/Config.mk``.
**Serial port:** you must set ``ESPTOOL_PORT`` to a non-empty value (for example
``/dev/ttyUSB0``). If it is unset or empty, the flash step fails.
Example::
$ export ESPTOOL_PORT=/dev/ttyUSB0
$ cmake --build build -t flash
Or for a single invocation::
$ ESPTOOL_PORT=/dev/ttyUSB0 cmake --build build -t flash
.. _esp32c6_debug:
CMake limitations
^^^^^^^^^^^^^^^^^^
The following is **not** supported when building with CMake yet; use the Make-based build instead:
* **ULP / LP core** — Low-power coprocessor support (``CONFIG_ESPRESSIF_USE_LP_CORE``) is
not wired up for CMake (ULP/LP integration is TODO).
Debugging
=========
This section describes debugging techniques for the ESP32-C6.
Debugging with ``openocd`` and ``gdb``
--------------------------------------
Espressif uses a specific version of OpenOCD to support ESP32-C6: `openocd-esp32 <https://github.com/espressif/>`_.
Please check `Building OpenOCD from Sources <https://docs.espressif.com/projects/esp-idf/en/release-v5.1/esp32c6/api-guides/jtag-debugging/index.html#jtag-debugging-building-openocd>`_
for more information on how to build OpenOCD for ESP32-C6.
You do not need an external JTAG to debug, the ESP32-C6 integrates a
USB-to-JTAG adapter.
.. note:: One must configure the USB drivers to enable JTAG communication. Please check
`Configure USB Drivers <https://docs.espressif.com/projects/esp-idf/en/release-v5.1/esp32c6/api-guides/jtag-debugging/configure-builtin-jtag.html#configure-usb-drivers>`_
for more information.
OpenOCD can then be used::
openocd -s <tcl_scripts_path> -c 'set ESP_RTOS hwthread' -f board/esp32c6-builtin.cfg -c 'init; reset halt; esp appimage_offset 0x0'
.. note::
- ``appimage_offset`` should be set to ``0x0`` when ``Simple Boot`` is used. For MCUboot, this value should be set to
``CONFIG_ESPRESSIF_OTA_PRIMARY_SLOT_OFFSET`` value (``0x10000`` by default).
- ``-s <tcl_scripts_path>`` defines the path to the OpenOCD scripts. Usually set to `tcl` if running openocd from its source directory.
It can be omitted if `openocd-esp32` were installed in the system with `sudo make install`.
If you want to debug with an external JTAG adapter it can
be connected as follows:
============ ===========
ESP32-C6 Pin JTAG Signal
============ ===========
GPIO4 TMS
GPIO5 TDI
GPIO6 TCK
GPIO7 TDO
============ ===========
Furthermore, an efuse needs to be burnt to be able to debug::
espefuse.py -p <port> burn_efuse DIS_USB_JTAG
.. warning:: Burning eFuses is an irreversible operation, so please
consider the above option before starting the process.
OpenOCD can then be used::
openocd -c 'set ESP_RTOS hwtread; set ESP_FLASH_SIZE 0' -f board/esp32c6-ftdi.cfg
Once OpenOCD is running, you can use GDB to connect to it and debug your application::
riscv-none-elf-gdb -x gdbinit nuttx
whereas the content of the ``gdbinit`` file is::
target remote :3333
set remote hardware-watchpoint-limit 2
mon reset halt
flushregs
monitor reset halt
thb nsh_main
c
.. note:: ``nuttx`` is the ELF file generated by the build process. Please note that ``CONFIG_DEBUG_SYMBOLS`` must be enabled in the ``menuconfig``.
Please refer to :doc:`/quickstart/debugging` for more information about debugging techniques.
Stack Dump and Backtrace Dump
-----------------------------
NuttX has a feature to dump the stack of a task and to dump the backtrace of it (and of all
the other tasks). This feature is useful to debug the system when it is not behaving as expected,
especially when it is crashing.
In order to enable this feature, the following options must be enabled in the NuttX configuration:
``CONFIG_SCHED_BACKTRACE``, ``CONFIG_DEBUG_SYMBOLS`` and, optionally, ``CONFIG_ALLSYMS``.
.. note::
The first two options enable the backtrace dump. The third option enables the backtrace dump
with the associated symbols, but increases the size of the generated NuttX binary.
Espressif also provides a tool to translate the backtrace dump into a human-readable format.
This tool is called ``btdecode.sh`` and is available at ``tools/espressif/btdecode.sh`` of NuttX
repository.
.. note::
This tool is not necessary if ``CONFIG_ALLSYMS`` is enabled. In this case, the backtrace dump
contains the function names.
Example - Crash Dump
^^^^^^^^^^^^^^^^^^^^
A typical crash dump, caused by an illegal load with ``CONFIG_SCHED_BACKTRACE`` and
``CONFIG_DEBUG_SYMBOLS`` enabled, is shown below::
riscv_exception: EXCEPTION: Store/AMO access fault. MCAUSE: 00000007, EPC: 420168ac, MT0
riscv_exception: PANIC!!! Exception = 00000007
_assert: Current Version: NuttX 10.4.0 2ae3246e40-dirty Sep 19 2024 14:47:41 risc-v
_assert: Assertion failed panic: at file: :0 task: backtrace process: backtrace 0x42016866
up_dump_register: EPC: 420168ac
up_dump_register: A0: 0000005a A1: 40809fc4 A2: 00000001 A3: 00000088
up_dump_register: A4: 00007fff A5: 00000001 A6: 00000000 A7: 00000000
up_dump_register: T0: 00000000 T1: 00000000 T2: ffffffff T3: 00000000
up_dump_register: T4: 00000000 T5: 00000000 T6: 00000000
up_dump_register: S0: 4080908e S1: 40809078 S2: 00000000 S3: 00000000
up_dump_register: S4: 00000000 S5: 00000000 S6: 00000000 S7: 00000000
up_dump_register: S8: 00000000 S9: 00000000 S10: 00000000 S11: 00000000
up_dump_register: SP: 4080a020 FP: 4080908e TP: 00000000 RA: 420168ac
dump_stack: User Stack:
dump_stack: base: 0x40809098
dump_stack: size: 00004040
dump_stack: sp: 0x4080a020
stack_dump: 0x4080a000: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00001880
stack_dump: 0x4080a020: 00000000 40808c90 42016866 42006e06 00000000 00000000 40809078 00000002
stack_dump: 0x4080a040: 00000000 00000000 00000000 42004d72 00000000 00000000 00000000 00000000
stack_dump: 0x4080a060: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
sched_dumpstack: backtrace| 2: 0x420168ac
dump_tasks: PID GROUP PRI POLICY TYPE NPX STATE EVENT SIGMASK STACKBASE STACKSIZE COMMAND
dump_tasks: ---- --- --- -------- ------- --- ------- ---------- ---------------- 0x40805a90 2048 irq
dump_task: 0 0 0 FIFO Kthread - Ready 0000000000000000 0x40807290 2032 Idle_Task
dump_task: 1 1 100 RR Task - Waiting Semaphore 0000000000000000 0x408081a8 1992 nsh_main
dump_task: 2 2 255 RR Task - Running 0000000000000000 0x40809098 4040 backtrace task
sched_dumpstack: backtrace| 0: 0x42008420
sched_dumpstack: backtrace| 1: 0x420089a2
sched_dumpstack: backtrace| 2: 0x420168ac
The lines starting with ``sched_dumpstack`` show the backtrace of the tasks. By checking it, it is
possible to track the root cause of the crash. Saving this output to a file and using the ``btdecode.sh``::
./tools/btdecode.sh esp32c6 /tmp/backtrace.txt
Backtrace for task 2:
0x420168ac: assert_on_task at backtrace_main.c:158
(inlined by) backtrace_main at backtrace_main.c:194
Backtrace dump for all tasks:
Backtrace for task 2:
0x420168ac: assert_on_task at backtrace_main.c:158
(inlined by) backtrace_main at backtrace_main.c:194
Backtrace for task 1:
0x420089a2: sys_call2 at syscall.h:227
(inlined by) up_switch_context at riscv_switchcontext.c:95
Backtrace for task 0:
0x42008420: up_idle at esp_idle.c:74
Peripheral Support
==================
The following list indicates the state of peripherals' support in NuttX:
============== ======= ====================
Peripheral Support NOTES
============== ======= ====================
ADC Yes Oneshot and internal temperature sensor
AES Yes
Bluetooth No
CAN/TWAI Yes
DMA Yes
ECC No
eFuse Yes
GPIO Yes Dedicated GPIO supported
HMAC No
I2C Yes Master and Slave mode also LPI2C supported
I2S Yes
LED/PWM Yes
MCPWM Yes
Pulse Counter Yes
RMT Yes
RNG Yes
RSA No
RTC Yes
SDIO No
SHA Yes
SPI Yes
SPIFLASH Yes
SPIRAM No
Temp. Sensor No
Timers Yes
UART Yes LPUART supported
USB Serial Yes
Watchdog Yes
Wi-Fi Yes
XTS No
============== ======= ====================
Analog-to-digital converter (ADC)
---------------------------------
One ADC unit is available for the ESP32-C6, with 7 channels.
During bringup, GPIOs for selected channels are configured automatically to be used as ADC inputs.
If available, ADC calibration is automatically applied (see
`this page <https://docs.espressif.com/projects/esp-idf/en/v5.1/esp32c6/api-reference/peripherals/adc_calibration.html>`__ for more details).
Otherwise, a simple conversion is applied based on the attenuation and resolution.
The ADC unit is accessible using the ADC character driver, which returns data for the enabled channels.
The ADC unit can be enabled in the menu :menuselection:`System Type --> Peripheral Support --> Analog-to-digital converter (ADC)`.
Then, it can be customized in the menu :menuselection:`System Type --> ADC Configuration`, which includes operating mode, gain and channels.
========== ===========
Channel ADC1 GPIO
========== ===========
0 0
1 1
2 2
3 3
4 4
5 5
6 6
========== ===========
.. _MCUBoot and OTA Update C6:
MCUBoot and OTA Update
======================
The ESP32-C6 supports over-the-air (OTA) updates using MCUBoot.
Read more about the MCUBoot for Espressif devices `here <https://docs.mcuboot.com/readme-espressif.html>`__.
Executing OTA Update
--------------------
This section describes how to execute OTA update using MCUBoot.
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 esp32c6-devkitc:mcuboot_update_agent
2. Build the MCUBoot bootloader::
make bootloader
3. Finally, build the application image::
make
Flash the image to the board and verify it boots ok.
It should show the message "This is MCUBoot Update Agent image" before NuttShell is ready.
At this point, the board should be able to connect to Wi-Fi so we can download a new binary from our network::
NuttShell (NSH) NuttX-12.4.0
This is MCUBoot Update Agent image
nsh>
nsh> wapi psk wlan0 <wifi_ssid> 3
nsh> wapi essid wlan0 <wifi_password> 1
nsh> renew wlan0
Now, keep the board as is and execute the following commands to **change the MCUBoot target slot to the 2nd slot**
and modify the message of the day (MOTD) as a mean to verify the new image is being used.
1. Change the MCUBoot target slot to the 2nd slot::
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!"
make olddefconfig
.. note::
The same changes can be accomplished through ``menuconfig`` in :menuselection:`System Type --> Bootloader and Image Configuration --> Target slot for image flashing`
for MCUBoot target slot and in :menuselection:`System Type --> Bootloader and Image Configuration --> Search (motd) --> NSH Library --> Message of the Day` for the MOTD.
2. Rebuild the application image::
make
At this point the board is already connected to Wi-Fi and has the primary image flashed.
The new image configured for the 2nd slot is ready to be downloaded.
To execute OTA, create a simple HTTP server on the NuttX directory so we can access the binary remotely::
cd nuttxspace/nuttx
python3 -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. Wait until image is transferred and the board should reboot automatically::
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%]
[.....]
Received: 1048576 of 1048576 bytes [100%]
Application Image successfully downloaded!
Requested update for next boot. Restarting...
NuttShell should now show the new MOTD, meaning the new image is being used::
NuttShell (NSH) NuttX-12.4.0
This is MCUBoot UPDATED image!
nsh>
Finally, 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.
Flash Encryption
----------------
Flash encryption is intended for encrypting the contents of the ESP32-C6'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.
The current state of flash encryption for ESP32-C6 allows the use of Virtual E-Fuses and development mode, which permit users to evaluate and test the firmware before making definitive changes such as burning E-Fuses.
Flash encryption supports the following features:
.. list-table::
:header-rows: 1
* - Feature
- Description
* - **Flash Encryption with Virtual E-Fuses**
- Use flash encryption without burning E-Fuses. Default selection when flash encryption is enabled.
* - **Flash Encryption in Development mode**
- Allows reflashing an encrypted device by appending the ``--encrypt`` argument to the ``esptool.py write_flash`` command. This is done automatically if ``ESPRESSIF_SECURE_FLASH_ENC_FLASH_DEVICE_ENCRYPTED`` is set.
* - **Flash Encryption in Release mode**
- Does not allow reflashing the device. This is a permanent setting.
* - **Flash Encryption key**
- A user-generated key is required by default. Alternatively, a device-generated key is possible, but it will not be recoverable by the user (not recommended). See ``ESPRESSIF_SECURE_FLASH_ENC_USE_HOST_KEY``.
* - **Encrypted MTD Partition**
- If SPI Flash is enabled, an empty user MTD partition will be automatically encrypted on first flash.
.. note::
It is **strongly suggested** to read the following before working on flash encryption:
- `MCUBoot Flash Encryption <https://docs.mcuboot.com/readme-espressif.html#flash-encryption>`_
- `General E-Fuse documentation <https://docs.espressif.com/projects/esp-idf/en/latest/esp32c6/api-reference/system/efuse.html>`_
- `Flash Encryption Relevant E-Fuses <https://docs.espressif.com/projects/esp-idf/en/latest/esp32c6/security/flash-encryption.html#relevant-efuses>`_
Flash Encryption Requirements
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Flash encryption requires burning E-Fuses to enable it on chip. This is not a reversible operation and should be done with caution.
There is, however, a way to test the flash encryption by simulating them on flash. Both paths are described below.
Build System Features
'''''''''''''''''''''
The build system contains some safeguards to avoid accidentally burning E-Fuses and automations for convenience. Those are summarized below:
1. A yellow warning will show up during build alerting that flash encryption is enabled (same for Virtual E-Fuses).
2. If ``ESPRESSIF_SECURE_FLASH_ENC_USE_HOST_KEY`` is set, build will fail if the flash encryption key is not found.
3. If SPI Flash is enabled, the user MTD partition is automatically encrypted with the provided encryption key.
4. ``make flash`` command will prompt the user for confirmation before burning the E-Fuse, if Virtual E-Fuses are disabled.
Simulating Flash Encryption with Virtual E-Fuses
'''''''''''''''''''''''''''''''''''''''''''''''''
It is highly recommended to use this method for testing the flash encryption before actually burning the E-Fuses.
The E-Fuses are stored in flash and persist between reboots. No real E-Fuses are changed.
To enable virtual E-Fuses for flash encryption testing, open ``menuconfig`` and:
1. Enable flash encryption on boot on: :menuselection:`System Type --> Bootloader and Image Configuration`
2. Verify Virtual E-Fuses are enabled (this is done by default): :menuselection:`System Type --> Peripheral Support --> E-Fuse support`
Now build the bootloader and the firmware. Flashing the device will trigger the following:
1. On the first boot, the bootloader will encrypt the flash::
...
[esp32c6] [WRN] eFuse virtual mode is enabled. If Secure boot or Flash encryption is enabled then it does not provide any security. FOR TESTING ONLY!
[esp32c6] [WRN] [efuse] [Virtual] try loading efuses from flash: 0x10000 (offset)
...
[esp32c6] [INF] [flash_encrypt] Encrypting bootloader...
[esp32c6] [INF] [flash_encrypt] Bootloader encrypted successfully
[esp32c6] [INF] [flash_encrypt] Encrypting primary slot...
[esp32c6] [INF] [flash_encrypt] Encrypting remaining flash...
[esp32c6] [INF] [flash_encrypt] Flash encryption completed
...
[esp32c6] [INF] Resetting with flash encryption enabled...
2. Device will reset and it should be now operating similar to an actual encrypted device::
...
[esp32c6] [INF] Checking flash encryption...
[esp32c6] [INF] [flash_encrypt] flash encryption is enabled (1 plaintext flashes left)
[esp32c6] [INF] Disabling RNG early entropy source...
[esp32c6] [INF] br_image_off = 0x20000
[esp32c6] [INF] ih_hdr_size = 0x20
[esp32c6] [INF] Loading image 0 - slot 0 from flash, area id: 1
...
NuttShell (NSH) NuttX-12.8.0
nsh>
Actual encryption and burning E-Fuses
'''''''''''''''''''''''''''''''''''''
E-Fuses are burned by esptool and the bootloader on the first boot after flashing with encryption enabled.
This process is automated on NuttX build system.
.. warning:: Burning E-Fuses is NOT a reversible operation and should be done with caution.
To build a firmware with E-Fuse support and flash encryption enabled, open ``menuconfig`` and:
1. Enable flash encryption on boot on: :menuselection:`System Type --> Bootloader and Image Configuration`
2. Disable Virtual E-Fuses :menuselection:`System Type --> Peripheral Support --> E-Fuse support`
3. Check usage mode is Development (this allows reflashing, while Release mode does not).
.. note:: If using development mode of flash encryption (see menuconfig and documentation above), it is still possible to re-flash the device with esptool by
setting ``ESPRESSIF_SECURE_FLASH_ENC_FLASH_DEVICE_ENCRYPTED`` which adds ``--encrypt`` argument to the ``esptool.py write_flash`` command.
This will apply the burned encryption key to the image while flashing.
Flash Allocation for MCUBoot
----------------------------
When MCUBoot is enabled on ESP32-C6, the flash memory is organized as follows
based on the default KConfig values:
**Flash Layout (MCUBoot Enabled)**
.. list-table::
:header-rows: 1
:widths: 40 20 20
:align: left
* - Region
- Offset
- Size
* - Bootloader
- 0x000000
- 64KB
* - E-Fuse Virtual (see Note)
- 0x010000
- 64KB
* - Primary Application Slot (/dev/ota0)
- 0x020000
- 1.4MB
* - Secondary Application Slot (/dev/ota1)
- 0x170000
- 1.4MB
* - Scratch Partition (/dev/otascratch)
- 0x2C0000
- 256KB
* - Storage MTD (optional)
- 0x300000
- 1MB
* - Available Flash
- 0x400000+
- Remaining
.. raw:: html
<div style="clear: both"></div>
**Note**: The E-Fuse Virtual region is optional and only used when
``ESPRESSIF_EFUSE_VIRTUAL_KEEP_IN_FLASH`` is enabled. However, this 64KB
location is always allocated in the memory layout to prevent accidental
erasure during board flashing operations, ensuring data preservation if
virtual E-Fuses are later enabled.
.. code-block:: text
Memory Map (Addresses in hex):
0x000000 ┌─────────────────────────────┐
│ │
│ MCUBoot Bootloader │
│ (64KB) │
│ │
0x010000 ├─────────────────────────────┤
│ E-Fuse Virtual │
│ (64KB) │
0x020000 ├─────────────────────────────┤
│ │
│ Primary App Slot │
│ (1.4MB) │
│ /dev/ota0 │
│ │
0x170000 ├─────────────────────────────┤
│ │
│ Secondary App Slot │
│ (1.4MB) │
│ /dev/ota1 │
│ │
0x2C0000 ├─────────────────────────────┤
│ │
│ Scratch Partition │
│ (256KB) │
│ /dev/otascratch │
│ │
0x300000 ├─────────────────────────────┤
│ │
│ Storage MTD (optional) │
│ (1MB) │
│ │
0x400000 ├─────────────────────────────┤
│ │
│ Available Flash │
│ (Remaining) │
│ │
└─────────────────────────────┘
The key KConfig options that control this layout:
- ``ESPRESSIF_OTA_PRIMARY_SLOT_OFFSET`` (default: 0x20000)
- ``ESPRESSIF_OTA_SECONDARY_SLOT_OFFSET`` (default: 0x170000)
- ``ESPRESSIF_OTA_SLOT_SIZE`` (default: 0x150000)
- ``ESPRESSIF_OTA_SCRATCH_OFFSET`` (default: 0x2C0000)
- ``ESPRESSIF_OTA_SCRATCH_SIZE`` (default: 0x40000)
- ``ESPRESSIF_STORAGE_MTD_OFFSET`` (default: 0x300000 when MCUBoot enabled)
- ``ESPRESSIF_STORAGE_MTD_SIZE`` (default: 0x100000)
For MCUBoot operation:
- The **Primary Slot** contains the currently running application
- The **Secondary Slot** receives OTA updates
- The **Scratch Partition** is used by MCUBoot for image swapping during updates
- MCUBoot manages image validation, confirmation, and rollback functionality
.. _esp32c6_ulp:
ULP LP Core Coprocessor
=======================
The ULP LP core (Low-power core) is a 32-bit RISC-V coprocessor integrated into the ESP32-C6 SoC.
It is designed to run independently of the main high-performance (HP) core and is capable of executing lightweight tasks
such as GPIO polling, simple peripheral control and I/O interactions.
This coprocessor benefits to offload simple tasks from HP core (e.g., GPIO polling , I2C operations, basic control logic) and
frees the main CPU for higher-level processing
For more information about ULP LP Core Coprocessor `check here <https://docs.espressif.com/projects/esp-idf/en/stable/esp32c6/api-reference/system/ulp-lp-core.html>`__.
Features of the ULP LP-Core
---------------------------
* Processor Architecture
- RV32I RISC-V core with IMAC extensions—Integer (I), Multiplication/Division (M), Atomic (A), and Compressed (C) instructions
- Runs at 20 MHz
* Memory
- Access to 16 KB of low-power memory (LP-RAM) and LP-domain peripherals any time
- Full access to all of the chip's memory and peripherals when when the HP core is active
* Debugging
- Built-in JTAG debug module for external debugging
- Supports LP UART for logging from the ULP itself
- Includes a panic handler capable of dumping register state via LP UART on exceptions
* Peripheral support
- LP domain peripherals (LP GPIO, LP I2C, LP UART and LP Timer)
- Full access HP domain peripherals when when the HP core is active
Loading Binary into ULP LP-Core
-------------------------------
There are two ways to load a binary into LP-Core:
- Using a prebuilt binary
- Using NuttX internal build system to build your own (bare-metal) application
When using a prebuilt binary, the already compiled output for the ULP system whether built from NuttX
or the ESP-IDF environment can be leveraged. However, whenever the ULP code needs to be modified, it must be rebuilt separately,
and the resulting .bin file has to be integrated into NuttX. This workflow, while compatible, can become tedious.
With NuttX internal build system, the ULP binary code can be built and flashed from a single location. It is more convenient but
using build system has some dependencies on example side.
Both methods requires ``CONFIG_ESPRESSIF_USE_LP_CORE`` variable to enable ULP core
and it can be set using ``make menuconfig`` or ``kconfig-tweak`` commands.
Additionally, a Makefile needs to be provided to specify the ULP application name,
source path of the ULP application, and either the binary (for prebuilt) or the source files (for internal build).
This Makefile must include the ULP makefile after the variable set process on ``arch/risc-v/src/common/espressif/esp_ulp.mk`` integration script.
For more information please refer to :ref:`ulp example Makefile. <ulp_makefile>`
Makefile Variables for ULP Core Build:
--------------------------------------
- ``ULP_APP_NAME``: Sets name for the ULP application. This variable also be used as prefix (e.g. ULP application bin variable name)
- ``ULP_APP_FOLDER``: Specifies the directory containing the ULP application's source codes.
- ``ULP_APP_BIN``: Defines the path of the prebuilt ULP binary.
- ``ULP_APP_C_SRCS``: Lists all C source files (.c) that need to be compiled for the ULP application.
- ``ULP_APP_ASM_SRCS``: Lists all assembly source files (.S or .s) to be assembled.
- ``ULP_APP_INCLUDES``: Specifies additional include directories for the compiler and assembler.
Here is an Makefile example when using prebuilt binary for ULP core:
.. code-block:: console
ULP_APP_NAME = esp_ulp
ULP_APP_FOLDER = $(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)$(CHIP_SERIES)
ULP_APP_BIN = $(TOPDIR)$(DELIM)Documentation$(DELIM)platforms$(DELIM)$(CONFIG_ARCH)$(DELIM)$(CONFIG_ARCH_CHIP)$(DELIM)boards$(DELIM)$(CONFIG_ARCH_BOARD)$(DELIM)ulp_riscv_blink.bin
include $(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)common$(DELIM)espressif$(DELIM)esp_ulp.mk
Here is an example for enabling ULP and using the prebuilt test binary for ULP core::
make distclean
./tools/configure.sh esp32c6-devkitc:nsh
kconfig-tweak -e CONFIG_ESPRESSIF_USE_LP_CORE
kconfig-tweak -e CONFIG_ESPRESSIF_ULP_USE_TEST_BIN
make olddefconfig
make -j
Creating an ULP LP-Core Application
-----------------------------------
To use NuttX's internal build system to compile the bare-metal LP binary, check the following instructions.
First, create a folder for the ULP source and header files into your NuttX example.
This folder is just for ULP project and it is an independent project. Therefore, the NuttX example guide should not be followed
for ULP example (folder location is irrelevant. It can be the same of the `nuttx-apps` repository, for instance).
To include the ULP folder in the build system, don't forget to include the ULP Makefile in the NuttX example Makefile. Lastly, configuration variables
needed to enable ULP core instructions can be found above.
NuttX's internal functions or POSIX calls are not supported.
Here is an example:
- ULP UART Snippet:
.. code-block:: C
#include <stdint.h>
#include "ulp_lp_core_print.h"
#include "ulp_lp_core_utils.h"
#include "ulp_lp_core_uart.h"
#include "ulp_lp_core_gpio.h"
#define nop() __asm__ __volatile__ ("nop")
int main (void)
{
while(1)
{
lp_core_printf("Hello from the LP core!!\r\n");
for (int i = 0; i < 10000; i++)
{
nop();
}
}
return 0;
}
For more information about ULP Core Coprocessor examples `check here <https://github.com/espressif/esp-idf/tree/master/examples/system/ulp/lp_core>`__.
After these settings follow the same steps as for any other configuration to build NuttX. Build system checks ULP project path,
adds every source and header file into project and builds it.
To sum up, here is an example. ``ulp_example/ulp (../ulp_example/ulp)`` folder selected as example
to create a subfolder for ULP but folder that includes ULP source code can be anywhere. For more information about
custom apps, please follow NuttX `Custom Apps How-to <https://nuttx.apache.org/docs/latest/guides/customapps.html#custom-apps-how-to>`__ guide,
this example will demonstrate how to add ULP code into a custom application:
- Tree view:
.. code-block:: text
nuttxspace/
├── nuttx/
└── apps/
└── ulp_example/
└── Makefile
└── Kconfig
└── ulp_example.c
└── ulp/
└── Makefile
└── ulp_main.c
- Contents in Makefile:
.. code-block:: console
include $(APPDIR)/Make.defs
PROGNAME = $(CONFIG_EXAMPLES_ULP_EXAMPLE_PROGNAME)
PRIORITY = $(CONFIG_EXAMPLES_ULP_EXAMPLE_PRIORITY)
STACKSIZE = $(CONFIG_EXAMPLES_ULP_EXAMPLE_STACKSIZE)
MODULE = $(CONFIG_EXAMPLES_ULP_EXAMPLE)
MAINSRC = ulp_example.c
include $(APPDIR)/Application.mk
include ulp/Makefile
- Contents in Kconfig:
.. code-block:: console
config EXAMPLES_ULP_EXAMPLE
bool "ULP Example"
default n
- Contents in ulp_example.c:
.. code-block:: C
#include <nuttx/config.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <inttypes.h>
#include <stdint.h>
#include <stdbool.h>
#include "ulp/ulp/ulp_main.h"
/* Files that holds ULP binary header */
#include "ulp/ulp/ulp_code.h"
int main (void)
{
int fd;
fd = open("/dev/ulp", O_WRONLY);
if (fd < 0)
{
printf("Failed to open ULP: %d\n", errno);
return -1;
}
/* ulp_example is the prefix which can be changed with ULP_APP_NAME makefile
* variable to access ULP binary code variable */
write(fd, ulp_example_bin, ulp_example_bin_len);
return 0;
}
.. _ulp_makefile:
- Contents in ulp/Makefile:
.. code-block:: console
ULP_APP_NAME = ulp_example
ULP_APP_FOLDER = $(APPDIR)$(DELIM)ulp_example$(DELIM)ulp
ULP_APP_C_SRCS = ulp_main.c
include $(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)common$(DELIM)espressif$(DELIM)esp_ulp.mk
- Contents in ulp_main.c:
.. code-block:: C
#include <stdint.h>
#include <stdbool.h>
#include "ulp_lp_core_gpio.h"
#define GPIO_PIN 0
#define nop() __asm__ __volatile__ ("nop")
bool gpio_level_previous = true;
int main (void)
{
while (1)
{
ulp_lp_core_gpio_set_level(GPIO_PIN, gpio_level_previous);
gpio_level_previous = !gpio_level_previous;
for (int i = 0; i < 10000; i++)
{
nop();
}
}
return 0;
}
- Command to build::
make distclean
./tools/configure.sh esp32c6-devkitc:nsh
kconfig-tweak -e CONFIG_ESPRESSIF_GPIO_IRQ
kconfig-tweak -e CONFIG_DEV_GPIO
kconfig-tweak -e CONFIG_ESPRESSIF_USE_LP_CORE
kconfig-tweak -e CONFIG_EXAMPLES_ULP_EXAMPLE
make olddefconfig
make -j
Here is an example of a single ULP application. However, support is not limited to just
one application. Multiple ULP applications are also supported.
By following the same guideline, multiple ULP applications can be created and loaded using ``write`` POSIX call.
Each NuttX application can build one ULP application. Therefore, to build multiple ULP applications, multiple NuttX
applications are needed to create each ULP binary. This limitation only applies when using the NuttX build system to
build multiple ULP applications; it does not affect the ability to load multiple ULP applications built by other means.
ULP binary can be included in NuttX application by adding
``#include "ulp/ulp/ulp_code.h"`` line. Then, the ULP binary is accessible by using the ULP application
prefix (defined by the ``ULP_APP_NAME`` variable in the ULP application Makefile) with the ``bin`` keyword to
access the binary data (e.g., if ``ULP_APP_NAME`` is ``ulp_test``, the binary variable will be ``ulp_test_bin``)
and ``bin_len`` keyword to access its length (e.g., ``ulp_test_bin_len`` for ``ULP_APP_NAME`` is ``ulp_test``).
Accessing the ULP LP-Core Program Variables
-------------------------------------------
Global symbols defined in the ULP application are available to the HP core through a shared memory region. To read or write ULP variables,
direct reading/writing to such memory positions are not allowed. POSIX calls are needed instead. To access the ULP variable through the HP core,
consider that its name is defined by the ULP application prefix (defined by the ``ULP_APP_NAME`` variable in the ULP application Makefile) + the ULP application variable.
For example if HP core tries to access a ULP application variable named ``result`` and ``ULP_APP_NAME`` in the ULP application Makefile set as ``ulp_app``, required name for
that variable will be ``ulp_app_result``.
``FIONREAD`` or ``FIONWRITE`` ioctl calls are, then, performed with the address of a ``struct symtab_s`` previously defined with the name of the variable to be read or written.
.. warning::
Ensure that the related ULP application is running. Otherwise, another ULP application may interfere by using the same memory space for a different variables.
Here is a snippet for reading and writing to a ULP variable named ``var_test`` (assuming the ``ULP_APP_NAME`` is set to ``ulp``) through the HP core:
.. code-block:: C
#include <nuttx/config.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include "nuttx/symtab.h"
int main (void)
{
uint32_t ulp_var;
int fd;
struct symtab_s sym =
{
.sym_name = "ulp_var_test",
.sym_value = &ulp_var,
};
fd = open("/dev/ulp", O_RDWR);
ioctl(fd, FIONREAD, &sym);
if (ulp_var != 0)
{
ulp_var = 0;
ioctl(fd, FIONWRITE, &sym);
}
return OK;
}
ULP LP-Core Wakeup Configuration
--------------------------------
By default, ULP LP-Core is woken up by HP core but other wakeup sources can be selected.
The available wakeup sources are:
* ``CONFIG_ESPRESSIF_ULP_WAKEUP_HP_CPU``: Wakeup by HP core
* ``CONFIG_ESPRESSIF_ULP_WAKEUP_LP_TIMER``: Wakeup by LP timer
* ``CONFIG_ESPRESSIF_ULP_WAKEUP_LP_UART``: Wakeup by LP UART activity
* ``CONFIG_ESPRESSIF_ULP_WAKEUP_LP_IO``: Wakeup by LP IO
Debugging ULP LP-Core
---------------------
To debug ULP LP-Core please first refer to :ref:`Debugging section. <esp32c6_debug>`
Debugging ULP core consist same steps with some small differences. First of all, configuration file
needs to be changed from ``board/esp32c6-builtin.cfg`` or ``board/esp32c6-ftdi.cfg`` to
``board/esp32c6-lpcore-builtin.cfg`` or ``board/esp32c6-lpcore-ftdi.cfg`` depending on preferred debug adapter.
LP core supports limited set of HW exceptions, so, for example, writing at address
0x0 will not cause a panic as it would be for the code running on HP core.
This can be overcome to some extent by enabling undefined behavior sanitizer for LP core application,
so ubsan can help to catch some errors. But note that it will increase code size significantly and
it can happen that application won't fit into RTC RAM.
To enable ubsan for ULP please add ``CONFIG_ESPRESSIF_ULP_ENABLE_UBSAN`` in menuconfig.
_`Managing esptool on virtual environment`
==========================================
This section describes how to install ``esptool``, ``imgtool`` or any other Python packages in a
proper environment.
Normally, a Linux-based OS would already have Python 3 installed by default. Up to a few years ago,
you could simply call ``pip install`` to install packages globally. However, this is no longer recommended
as it can lead to conflicts between packages and versions. The recommended way to install Python packages
is to use a virtual environment.
A virtual environment is a self-contained directory that contains a Python installation for a particular
version of Python, plus a number of additional packages. You can create a virtual environment for each
project you are working on, and install the required packages in that environment.
Two alternatives are explained below, you can select any one of those.
Using pipx (recommended)
------------------------
``pipx`` is a tool that makes it easy to install Python packages in a virtual environment. To install
``pipx``, you can run the following command (using apt as example)::
$ apt install pipx
Once you have installed ``pipx``, you can use it to install Python packages in a virtual environment. For
example, to install the ``esptool`` package, you can run the following command::
$ pipx install esptool
This will create a new virtual environment in the ``~/.local/pipx/venvs`` directory, which contains the
``esptool`` package. You can now use the ``esptool`` command as normal, and so will the build system.
Make sure to run ``pipx ensurepath`` to add the ``~/.local/bin`` directory to your ``PATH``. This will
allow you to run the ``esptool`` command from any directory.
Using venv (alternative)
------------------------
To create a virtual environment, you can use the ``venv`` module, which is included in the Python standard
library. To create a virtual environment, you can run the following command::
$ python3 -m venv myenv
This will create a new directory called ``myenv`` in the current directory, which contains a Python
installation and a copy of the Python standard library. To activate the virtual environment, you can run
the following command::
$ source myenv/bin/activate
This will change your shell prompt to indicate that you are now working in the virtual environment. You can
now install packages using ``pip``. For example, to install the ``esptool`` package, you can run the following
command::
$ pip install esptool
This will install the ``esptool`` package in the virtual environment. You can now use the ``esptool`` command as
normal. When you are finished working in the virtual environment, you can deactivate it by running the following
command::
$ deactivate
This will return your shell prompt to its normal state. You can reactivate the virtual environment at any time by
running the ``source myenv/bin/activate`` command again. You can also delete the virtual environment by deleting
the directory that contains it.
Supported Boards
================
.. toctree::
:glob:
:maxdepth: 1
boards/*/*
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