ESP32-S2 family
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Specific properties of ESP32-S2 variant (family)

Specific properties of ESP32-S2 variant (family)

Author
Gunar Schorcht gunar.nosp@m.@sch.nosp@m.orcht.nosp@m..net

Specific properties of ESP32-S2 variant (family)

Embedded Flash and SPI RAM

There are many different versions of the ESP32-S2 chip and ESP32-S2 modules used on ESP32-S2 boards. They differ in the size of embedded Flash and SPI RAM as well as used SPI mode for Flash and SPI RAM. These differences allow dozens of different versions of a board. For example, there are 8 versions of the ESP32-S2 DevKitC-1 board with different flash and SPI RAM sizes.

Chip Flash (Mode) SPI RAM (Mode)
ESP32-S2 - -
ESP32-S2FH2 2 MB (Quad SPI) -
ESP32-S2FH4 4 MB (Quad SPI) -
ESP32-S2FN4R2 4 MB (Quad SPI) 2 MB (Quad SPI)
ESP32-S2R2 - 2 MB (Quad SPI)


Module Chip Flash (Mode) SPI RAM (Mode)
ESP32-S2-MINI-1x-H4 ESP32-S2FH4 4 MB (Quad SPI) -
ESP32-S2-MINI-1x-N4 ESP32-S2FH4 4 MB (Quad SPI) -
ESP32-S2-MINI-1x-N4R2 ESP32-S2N4R2 4 MB (Quad SPI) 2 MB (Quad SPI)
ESP32-S2-SOLO-H4 ESP32-S2 4 MB (Quad SPI) -
ESP32-S2-SOLO-N4 ESP32-S2 4 MB (Quad SPI) -
ESP32-S2-SOLO-N4R2 ESP32-S2R2 4 MB (Quad SPI) 2 MB (Quad SPI)
ESP32-S2-WROOM ESP32-S2 4 MB (Quad SPI) -
ESP32-S2-WROVER ESP32-S2 4 MB (Quad SPI) 2 MB (Quad SPI)

x Stands for the module versions with and without U (external antenna connector).

Depending on the chip or module used, it has to be specified as a feature in the board definition whether SPI RAM is available (feature esp_spi_ram).

If the feature esp_spi_ram is given, the SPI RAM can be used as heap by using the pseudo module esp_spi_ram.

If Quad SPI mode is used, GPIO26 ... GPIO32 are occupied and cannot be used for other purposes. In case of Octal SPI mode, the pseudomodule esp_spi_oct is additionally enabled and GPIO33 ... GPIO37 are occupied if the SPI RAM is enabled by using the pseudomodule esp_spi_ram. GPIO33 ... GPIO37 are then not available for other purposes. Conflicts may occur when using these GPIOs.

GPIO pins

ESP32-S2 has 45 GPIO pins, where a subset can be used as ADC channel and as low-power digital input/output in deep-sleep mode, the so-called RTC GPIOs. Some of them are used by special SoC components and are not broken out on all ESP32-S2 modules. The following table gives a short overview.

Pin Type ADC RTC PU / PD Special function Remarks
GPIO0 In/Out - X X - Bootstrapping
GPIO1 In/Out X X X - -
GPIO2 In/Out X X X - -
GPIO3 In/Out X X X - Bootstrapping
GPIO4 In/Out X X X - -
GPIO5 In/Out X X X - -
GPIO6 In/Out X X X - -
GPIO7 In/Out X X X - -
GPIO8 In/Out X X X - -
GPIO9 In/Out X X X - -
GPIO10 In/Out X X X - -
GPIO11 In/Out X X X - -
GPIO12 In/Out X X X - -
GPIO13 In/Out X X X - -
GPIO14 In/Out X X X - -
GPIO15 In/Out X X X XTAL_32K_P External 32k crystal
GPIO16 In/Out X X X XTAL_32K_N External 32k crystal
GPIO17 In/Out X X X DAC1 -
GPIO18 In/Out X X X DAC2 -
GPIO19 In/Out X X X USB D- USB 2.0 OTG / USB-JTAG bridge
GPIO20 In/Out X X X USB D+ USB 2.0 OTG / USB-JTAG bridge
GPIO21 In/Out - X X - -
GPIO26 In/Out - - X Flash/PSRAM SPICS1 not available if SPI RAM is used
GPIO27 In/Out - - X Flash/PSRAM SPIHD not available
GPIO28 In/Out - - X Flash/PSRAM SPIWP not available
GPIO29 In/Out - - X Flash/PSRAM SPICS0 not available
GPIO30 In/Out - - X Flash/PSRAM SPICLK not available
GPIO31 In/Out - - X Flash/PSRAM SPIQ not available
GPIO32 In/Out - - X Flash/PSRAM SPID not available
GPIO33 In/Out - - X Flash/PSRAM SPIQ4 not available if octal Flash or SPI RAM is used
GPIO34 In/Out - - X Flash/PSRAM SPIQ5 not available if octal Flash or SPI RAM is used
GPIO35 In/Out - - X Flash/PSRAM SPIQ6 not available if octal Flash or SPI RAM is used
GPIO36 In/Out - - X Flash/PSRAM SPIQ7 not available if octal Flash or SPI RAM is used
GPIO37 In/Out - - X Flash/PSRAM SPIQ8 not available if octal Flash or SPI RAM is used
GPIO38 In/Out - - X Flash/PSRAM SPIDQS not available if octal Flash or SPI RAM is used
GPIO39 In/Out - - X MTCK JTAG interface
GPIO40 In/Out - - X MTDO JTAG interface
GPIO41 In/Out - - X MTDI JTAG interface
GPIO42 In/Out - - X MTMS JTAG interface
GPIO43 In/Out - - X UART0 TX Console
GPIO44 In/Out - - X UART0 RX Console
GPIO45 In/Out - - X - Bootstrapping (0 - 3.3V, 1 - 1.8V)
GPIO46 In/Out - - X - Bootstrapping
GPIO47 In/Out - - X SPICLK_P -
GPIO48 In/Out - - X SPICLK_N -

PSRAM - Stands for pseudo-static RAM and refers to the SPI RAM.

ADC: Pins that can be used as ADC channels.
RTC: Pins that are RTC GPIOs and can be used in deep-sleep mode.
PU/PD: Pins that have software configurable pull-up/pull-down functionality.

GPIO0, GPIO3, GPIO45 and GPIO46 are bootstrapping. GPIO0 and GPIO46 pins are used to boot ESP32-S2 in different modes:

GPIO0 GPIO46 Mode
1 X SPI Boot mode to boot the firmware from flash (default mode)
0 1 Download Boot mode for flashing the firmware


If EFUSE_STRAP_JTAG_SEL is set, GPIO3 is used to select the interface that is used as JTAG interface.

GPIO3 Mode
1 USB-JTAG bridge at GPIO19 and GPIO20 is used as JTAG interface
0 GPIO39 to GPIO42 are used as JTAG interface


Note
If EFUSE_DIS_USB_JTAG or EFUSE_DIS_PAD_JTAG are set, the interface selection is fixed and GPIO3 is not used as bootstrapping pin.

GPIO45 is used to select the voltage VDD_SPI for the Flash/PSRAM interfaces SPI0 and SPI1.

ADC Channels

ESP32-S2 integrates two 12-bit ADCs (ADC1 and ADC2) with 20 channels in total:

Note
  • ADC2 is also used by the WiFi module. The GPIOs connected to ADC2 are therefore not available as ADC channels if the modules esp_wifi or esp_now are used.
  • GPIO3 is a strapping pin und shouldn't be used as ADC channel

DAC Channels

ESP32 SoC supports 2 DAC lines at GPIO17 and GPIO18.

I2C Interfaces

ESP32-S2 has two built-in I2C interfaces.

The following table shows the default configuration of I2C interfaces used for ESP32-S2 boards. It can be overridden by application-specific configurations.

Device Signal Pin Symbol Remarks
I2C_DEV(0) #I2C0_SPEED default is I2C_SPEED_FAST
I2C_DEV(0) SCL GPIO9 #I2C0_SCL -
I2C_DEV(0) SDA GPIO8 #I2C0_SDA -


PWM Channels

The ESP32-S2 LEDC module has 1 channel group with 8 channels. Each of these channels can be clocked by one of the 4 timers.

SPI Interfaces

ESP32-S2 has four SPI controllers where SPI0 and SPI1 share the same bus and can only operate in memory mode while SPI2 and SPI3 can be used as general purpose SPI:

Thus, SPI2 (FSPI) and SPI3 can be used as general purpose SPI in RIOT as SPI_DEV(0) and SPI_DEV(1) by defining the symbols SPI0_* and SPI1_*.

The following table shows the pin configuration used by default, even though it can vary from board to board.

Device Signal Pin Symbol Remarks
SPI0_HOST/SPI1_HOST SPICS0 GPIO29 - reserved for flash and PSRAM
SPI0_HOST/SPI1_HOST SPICS1 GPIO26 - reserved for flash and PSRAM
SPI0_HOST/SPI1_HOST SPICLK GPIO30 - reserved for flash and PSRAM
SPI0_HOST/SPI1_HOST SPID GPIO32 - reserved for flash and PSRAM
SPI0_HOST/SPI1_HOST SPIQ GPIO31 - reserved for flash and PSRAM
SPI0_HOST/SPI1_HOST SPIHD GPIO27 - reserved for flash and PSRAM (only in qio or qout mode)
SPI0_HOST/SPI1_HOST SPIWP GPIO28 - reserved for flash and PSRAM (only in qio or qout mode)
SPI0_HOST/SPI1_HOST SPIIO4 GPIO33 - reserved for Flash and PSRAM (only in octal mode)
SPI0_HOST/SPI1_HOST SPIIO5 GPIO34 - reserved for Flash and PSRAM (only in octal mode)
SPI0_HOST/SPI1_HOST SPIIO6 GPIO35 - reserved for Flash and PSRAM (only in octal mode)
SPI0_HOST/SPI1_HOST SPIIO7 GPIO36 - reserved for Flash and PSRAM (only in octal mode)
SPI0_HOST/SPI1_HOST SPIDQA GPIO37 - reserved for Flash and PSRAM (only in octal mode)
SPI2_HOST (FSPI) SCK GPIO12 #SPI0_SCK can be used
SPI2_HOST (FSPI) MOSI GPIO11 #SPI0_MOSI can be used
SPI2_HOST (FSPI) MISO GPIO13 #SPI0_MISO can be used
SPI2_HOST (FSPI) CS0 GPIO10 #SPI0_CS0 can be used


Timers

ESP32-S2 has two timer groups with two timers each, resulting in a total of four timers. Since one timer is used as system timer, up to three timers with one channel each can be used in RIOT as timer devices TIMER_DEV(0) ... TIMER_DEV(2).

Additionally ESP32-S2 has three CCOMPARE registers which can be used alternatively as timer devices TIMER_DEV(0) ... TIMER_DEV(2) can be used in RIOT if the module esp_hw_counter is enabled.

UART Interfaces

ESP32 integrates three UART interfaces. The following default pin configuration of UART interfaces as used by a most boards can be overridden by the application, see section Application-Specific Configurations.

Device Signal Pin Symbol Remarks
UART_DEV(0) TxD GPIO43 #UART0_TXD cannot be changed
UART_DEV(0) RxD GPIO44 #UART0_RXD cannot be changed
UART_DEV(1) TxD GPIO17 #UART1_TXD optional, can be overridden
UART_DEV(1) RxD GPIO18 #UART1_RXD optional, can be overridden
UART_DEV(2) TxD - UART2_TXD optional, can be overridden
UART_DEV(2) RxD - UART2_RXD optional, can be overridden


JTAG Interface

There are two options on how to use the JTAG interface on ESP32-S2:

  1. Using the built-in USB-to-JTAG bridge connected to an USB cable as follows:
    USB Signal ESP32-S2 Pin
    D- (white) GPIO19
    D+ (green) GPIO20
    V_Bus (red) 5V
    Ground (black) GND

    Note
    This option requires that the USB D- and USB D+ signals are connected to the ESP32-S2 USB interface at GPIO19 and GPIO20.
  2. Using an external JTAG adapter connected to the JTAG interface exposed to GPIOs as follows:
    JTAG Signal ESP32S2 Pin
    TRST_N CHIP_PU
    TDO GPIO40 (MTDO)
    TDI GPIO41 (MTDI)
    TCK GPIO39 (MTCK)
    TMS GPIO42 (MTMS)
    GND GND

Using the built-in USB-to-JTAG is the default option, i.e. the JTAG interface of the ESP32-S2 is connected to the built-in USB-to-JTAG bridge. To use an external JTAG adapter, the JTAG interface of the ESP32-S2 has to be connected to the GPIOs as shown above. For this purpose eFuses have to be burned with the following command:

espefuse.py burn_efuse JTAG_SEL_ENABLE --port /dev/ttyUSB0

Once the eFuses are burned with this command and option JTAG_SEL_ENABLE, GPIO3 is used as a bootstrapping pin to choose between the two options. If GPIO3 is HIGH when ESP32-S2 is reset, the JTAG interface is connected to the built-in USB to JTAG bridge and the USB cable can be used for on-chip debugging. Otherwise, the JTAG interface is exposed to GPIO39 ... GPIO42 and an external JTAG adapter has to be used.

Alternatively, the integrated USB-to-JTAG bridge can be permanently disabled with the following command:

espefuse.py burn_efuse DIS_USB_JTAG --port /dev/ttyUSB0

Once the eFuses are burned with this command and option DIS_USB_JTAG, the JTAG interface is always exposed to GPIO4 ... GPIO7 and an external JTAG adapter has to be used.

Note
Burning eFuses is an irreversible operation.

For more information about JTAG configuration for ESP32-S2, refer to the section Configure Other JTAG Interface in the ESP-IDF documentation.