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

System requirements

Prerequisites

Espressif HAL requires binary blobs in order work. The west extension below performs the required syncronization to clone, checkout and pull the submodules:

west espressif update

Note

It is recommended running the command above after west update.

Building & Flashing

Build and flash applications as usual (see Building an Application and Run an Application for more details).

# From the root of the zephyr repository
west build -b esp32 samples/hello_world

The usual flash target will work with the esp32 board configuration. Here is an example for the Hello World application.

# From the root of the zephyr repository
west build -b esp32 samples/hello_world
west flash

Open the serial monitor using the following command:

west espressif monitor

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

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

Debugging

As with much custom hardware, the ESP32 modules require patches to OpenOCD that are not upstreamed. Espressif maintains their own fork of the project. The custom OpenOCD can be obtained by running the following extension:

west espressif install

Note

By default, the OpenOCD will be downloaded and installed under $HOME/.espressif/tools/zephyr directory (%USERPROFILE%/.espressif/tools/zephyr on Windows).

The Zephyr SDK uses a bundled version of OpenOCD by default. You can overwrite that behavior by adding the -DOPENOCD=<path/to/bin/openocd> -DOPENOCD_DEFAULT_PATH=<path/to/openocd/share/openocd/scripts> parameter when building.

Here is an example for building the Hello World application.

# From the root of the zephyr repository
west build -b esp32 samples/hello_world -- -DOPENOCD=<path/to/bin/openocd> -DOPENOCD_DEFAULT_PATH=<path/to/openocd/share/openocd/scripts>
west flash

You can debug an application in the usual way. Here is an example for the Hello World application.

# From the root of the zephyr repository
west build -b esp32 samples/hello_world
west debug

Using JTAG

On the ESP-WROVER-KIT board, the JTAG pins are connected internally to a USB serial port on the same device as the console. These boards require no external hardware and are debuggable as-is. The JTAG signals, however, must be jumpered closed to connect the internal controller (the default is to leave them disconnected). The jumper headers are on the right side of the board as viewed from the power switch, next to similar headers for SPI and UART. See ESP-WROVER-32 V3 Getting Started Guide for details.

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

Once the device is connected, you should be able to connect with (for a DevKitC board, replace with esp32-wrover.cfg for WROVER):

cd ~/esp/openocd-esp32
src/openocd -f interface/ftdi/flyswatter2.cfg -c 'set ESP32_ONLYCPU 1' -c 'set ESP32_RTOS none' -f board/esp-wroom-32.cfg -s tcl

The ESP32_ONLYCPU setting is critical: without it OpenOCD will present only the “APP_CPU” via the gdbserver, and not the “PRO_CPU” on which Zephyr is running. It’s currently unexplored as to whether the CPU can be switched at runtime or if breakpoints can be set for either/both.

Now you can connect to openocd with gdb and point it to the OpenOCD gdbserver running (by default) on localhost port 3333. Note that you must use the gdb distributed with the ESP-32 SDK. Builds off of the FSF mainline get inexplicable protocol errors when connecting.

~/esp/xtensa-esp32-elf/bin/xtensa-esp32-elf-gdb outdir/esp32/zephyr.elf
(gdb) target remote localhost:3333

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

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.

References

1

https://en.wikipedia.org/wiki/ESP32