.. _esp32:

ESP32
#####

Overview
********

ESP32 is a series of low cost, low power system on a chip microcontrollers
with integrated Wi-Fi & dual-mode Bluetooth.  The ESP32 series employs a
Tensilica Xtensa LX6 microprocessor in both dual-core and single-core
variations.  ESP32 is created and developed by Espressif Systems, a
Shanghai-based Chinese company, and is manufactured by TSMC using their 40nm
process. [1]_

The features include the following:

- Dual core Xtensa microprocessor (LX6), running at 160 or 240MHz
- 520KB of SRAM
- 802.11b/g/n/e/i
- Bluetooth v4.2 BR/EDR and BLE
- Various peripherals:

  - 12-bit ADC with up to 18 channels
  - 2x 8-bit DACs
  - 10x touch sensors
  - Temperature sensor
  - 4x SPI
  - 2x I2S
  - 2x I2C
  - 3x UART
  - SD/SDIO/MMC host
  - Slave (SDIO/SPI)
  - Ethernet MAC
  - CAN bus 2.0
  - IR (RX/TX)
  - Motor PWM
  - LED PWM with up to 16 channels
  - Hall effect sensor

- Cryptographic hardware acceleration (RNG, ECC, RSA, SHA-2, AES)
- 5uA deep sleep current

Supported Features
==================

Current Zephyr's ESP32-devkitc board supports the following features:

+------------+------------+-------------------------------------+
| Interface  | Controller | Driver/Component                    |
+============+============+=====================================+
+------------+------------+-------------------------------------+
| UART       | on-chip    | serial port                         |
+------------+------------+-------------------------------------+
| GPIO       | on-chip    | gpio                                |
+------------+------------+-------------------------------------+
| PINMUX     | on-chip    | pinmux                              |
+------------+------------+-------------------------------------+
| USB-JTAG   | on-chip    | hardware interface                  |
+------------+------------+-------------------------------------+
| SPI Master | on-chip    | spi                                 |
+------------+------------+-------------------------------------+
| Timers     | on-chip    | counter                             |
+------------+------------+-------------------------------------+
| Watchdog   | on-chip    | watchdog                            |
+------------+------------+-------------------------------------+
| TRNG       | on-chip    | entropy                             |
+------------+------------+-------------------------------------+
| LEDC       | on-chip    | pwm                                 |
+------------+------------+-------------------------------------+
| MCPWM      | on-chip    | pwm                                 |
+------------+------------+-------------------------------------+
| PCNT       | on-chip    | qdec                                |
+------------+------------+-------------------------------------+
| SPI DMA    | on-chip    | spi                                 |
+------------+------------+-------------------------------------+
| TWAI       | on-chip    | can                                 |
+------------+------------+-------------------------------------+
| ADC        | on-chip    | adc                                 |
+------------+------------+-------------------------------------+
| DAC        | on-chip    | dac                                 |
+------------+------------+-------------------------------------+
| Wi-Fi      | on-chip    |                                     |
+------------+------------+-------------------------------------+
| Bluetooth  | on-chip    |                                     |
+------------+------------+-------------------------------------+

System requirements
===================

Prerequisites
-------------

Espressif HAL requires WiFi and Bluetooth binary blobs in order work. Run the command
below to retrieve those files.

.. code-block:: console

   west blobs fetch hal_espressif

.. note::

   It is recommended running the command above after :file:`west update`.

Building & Flashing
*******************

ESP-IDF bootloader
==================

The board is using the ESP-IDF bootloader as the default 2nd stage bootloader.
It is build as a subproject at each application build. No further attention
is expected from the user.

MCUboot bootloader
==================

User may choose to use MCUboot bootloader instead. In that case the bootloader
must be build (and flash) at least once.

There are two options to be used when building an application:

1. Sysbuild
2. Manual build

.. note::

   User can select the MCUboot bootloader by adding the following line
   to the board default configuration file.
   ```
   CONFIG_BOOTLOADER_MCUBOOT=y
   ```

Sysbuild
========

The sysbuild makes possible to build and flash all necessary images needed to
bootstrap the board with the EPS32 SoC.

To build the sample application using sysbuild use the command:

.. zephyr-app-commands::
   :tool: west
   :app: samples/hello_world
   :board: esp32
   :goals: build
   :west-args: --sysbuild
   :compact:

By default, the ESP32 sysbuild creates bootloader (MCUboot) and application
images. But it can be configured to create other kind of images.

Build directory structure created by sysbuild is different from traditional
Zephyr build. Output is structured by the domain subdirectories:

.. code-block::

  build/
  ├── hello_world
  │   └── zephyr
  │       ├── zephyr.elf
  │       └── zephyr.bin
  ├── mcuboot
  │    └── zephyr
  │       ├── zephyr.elf
  │       └── zephyr.bin
  └── domains.yaml

.. note::

   With ``--sysbuild`` option the bootloader will be re-build and re-flash
   every time the pristine build is used.

For more information about the system build please read the :ref:`sysbuild` documentation.

Manual build
============

During the development cycle, it is intended to build & flash as quickly possible.
For that reason, images can be build one at a time using traditional build.

The instructions following are relevant for both manual build and sysbuild.
The only difference is the structure of the build directory.

.. note::

   Remember that bootloader (MCUboot) needs to be flash at least once.

Build and flash applications as usual (see :ref:`build_an_application` and
:ref:`application_run` for more details).

.. zephyr-app-commands::
   :zephyr-app: samples/hello_world
   :board: esp32
   :goals: build

The usual ``flash`` target will work with the ``esp32`` board
configuration. Here is an example for the :ref:`hello_world`
application.

.. zephyr-app-commands::
   :zephyr-app: samples/hello_world
   :board: esp32
   :goals: flash

Open the serial monitor using the following command:

.. code-block:: shell

   west espressif monitor

After the board has automatically reset and booted, you should see the following
message in the monitor:

.. code-block:: console

   ***** Booting Zephyr OS vx.x.x-xxx-gxxxxxxxxxxxx *****
   Hello World! esp32

Debugging
*********

ESP32 support on OpenOCD is available upstream as of version 0.12.0.
Download and install OpenOCD from `OpenOCD`_.

On the ESP-WROOM-32 DevKitC board, the JTAG pins are not run to a
standard connector (e.g. ARM 20-pin) and need to be manually connected
to the external programmer (e.g. a Flyswatter2):

+------------+-----------+
| ESP32 pin  | JTAG pin  |
+============+===========+
| 3V3        | VTRef     |
+------------+-----------+
| EN         | nTRST     |
+------------+-----------+
| IO14       | TMS       |
+------------+-----------+
| IO12       | TDI       |
+------------+-----------+
| GND        | GND       |
+------------+-----------+
| IO13       | TCK       |
+------------+-----------+
| IO15       | TDO       |
+------------+-----------+

Further documentation can be obtained from the SoC vendor in `JTAG debugging
for ESP32`_.

Here is an example for building the :ref:`hello_world` application.

.. zephyr-app-commands::
   :zephyr-app: samples/hello_world
   :board: esp32
   :goals: build flash

You can debug an application in the usual way. Here is an example for the :ref:`hello_world` application.

.. zephyr-app-commands::
   :zephyr-app: samples/hello_world
   :board: esp32
   :goals: debug

Note on Debugging with GDB Stub
===============================

GDB stub is enabled on ESP32.

* When adding breakpoints, please use hardware breakpoints with command
  ``hbreak``. Command ``break`` uses software breakpoints which requires
  modifying memory content to insert break/trap instructions.
  This does not work as the code is on flash which cannot be randomly
  accessed for modification.

.. _`JTAG debugging for ESP32`: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/jtag-debugging/index.html
.. _`OpenOCD`: https://github.com/openocd-org/openocd

References
**********

.. [1] https://en.wikipedia.org/wiki/ESP32
.. _ESP32 Technical Reference Manual: https://espressif.com/sites/default/files/documentation/esp32_technical_reference_manual_en.pdf
.. _Hardware Reference: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/hw-reference/index.html