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gpio_expander (examples/gpio_expander/)

Drives CP-side GPIOs from the host as if the coprocessor were a remote GPIO expander. The host calls esp_hosted_cp_gpio_* (configure / set level / get level / reset) over RPC; the CP applies each call to its own gpio_* peripheral. Useful when the host MCU runs out of pins and the coprocessor has spare ones.

Supported Platforms and Transports

Supported Coprocessors

Coprocessor ESP32 ESP32-C Series ESP32-S Series
Support Yes Yes Yes

Supported Host Devices

Host Device ESP32-P4 ESP32-H2 Other MCUs Linux
Support Yes Yes Yes Yes

Supported Connection buses

Connection bus SDIO SPI Full-Duplex SPI Half-Duplex UART
Linux host Yes Yes No No
MCU host Yes Yes Yes Yes

Directory layout

gpio_expander/
├── cp/                  ESP coprocessor firmware
├── mcu_host/            ESP-IDF MCU host app
└── linux_802_3_host/    Linux host
     ├── c_app/          native C app
     ├── kmod/           kernel module
     └── py_app/         Python (ctypes) app

Linux Linux Host Setup

1. Coprocessor
2. Linux Host

MCU MCU Host Setup

1. Coprocessor
2. MCU Host

Scenario

The host drives and reads the co-processor's GPIOs remotely over the control path (RPC).

sequenceDiagram
    participant App as Host app
    participant CP as Co-processor GPIO
    App->>CP: esp_hosted_cp_gpio_config(pin) (RPC)
    App->>CP: esp_hosted_cp_gpio_set_level(pin, 1) (RPC)
    CP-->>App: ok
    App->>CP: esp_hosted_cp_gpio_get_level(pin) (RPC)
    CP-->>App: level
Loading

Important

New here? Get a base example working first. Follow Getting Started: Linux or Getting Started: MCU to wire the boards, install tools, choose a transport, and confirm the host↔co-processor handshake. The steps below only add what is specific to this example.

Linux Linux Host Setup

1. Coprocessor

Set up the tools once (from the repo root):

cd /path/to/esp_hosted
./install.sh      # install.fish for the fish shell
. ./export.sh     # . ./export.fish for the fish shell

GPIO-expander support is enabled by the co-processor's sdkconfig.defaults (ESP_HOSTED_CP_FEAT_GPIO_EXP) — no extra option to enable. Select the transport via eh.py menuconfig:

cd examples/gpio_expander/cp
eh.py set-target esp32c6
eh.py menuconfig
Component config
└── ESP-Hosted
     └── Configure coprocessor
          └── CP transport
               ├── Communication bus (co-processor <== bus ==> host)
               │    ├── ( ) SPI Full Duplex
               │    ├── (X) SDIO                    <── default
               │    ├── ( ) SPI Half Duplex         ← MCU host only
               │    └── ( ) UART                    ← MCU host only
               └── SDIO Configuration               ← clock, GPIOs, checksum (defaults OK)

The CP-side pin under test (default GPIO 2) is set in code via SLAVE_GPIO_PIN. Each bus has its own settings submenu (pins, clock, checksum) — defaults are fine for bring-up.

The CP dependency config is pre-set in sdkconfig.defaults (do not remove):

CONFIG_ESP_HOSTED_CP_FEAT_GPIO_EXP=y           # CP GPIO-expander feature
CONFIG_BT_ENABLED=n                            # BT off (unused by this example)

Then flash and monitor:

eh.py -p <cp_usb_serial_port> flash monitor

2. Linux Host

Note

Base wiring, OS setup, and transport bring-up live in Getting Started: Linux. This section assumes that already works.

Set up the tools once (from the repo root):

cd /path/to/esp_hosted
./install.sh      # install.fish for the fish shell
. ./export.sh     # . ./export.fish for the fish shell

Kernel module (creates ethsta0 / ethap0 and /dev/esps0):

cd examples/gpio_expander/linux_802_3_host/kmod
./build.sh --bus sdio --reload --reset-gpio 518 --clock-mhz 50
# SPI instead: ./build.sh --bus spi --reload --reset-gpio 518 --clock-mhz 10 --spi-mode 3

--reload builds, unloads, and reloads with the given module params. On SPI, start at --clock-mhz 10; once stable, raise it in steps to the co-processor's max SPI clock (see Performance).

Native C app:

cd examples/gpio_expander/linux_802_3_host/c_app
eh.py set-target linux
eh.py menuconfig
Example Configuration
└── [ ] Use legacy esp_hosted_* compat-surface main    <── default off

The Host dependency config is pre-set in sdkconfig.defaults (do not remove):

CONFIG_ESP_HOSTED_HOST_FEAT_GPIO_EXP=y         # host GPIO-expander feature
CONFIG_ESP_HOSTED_HOST_FEAT_RPC=y              # RPC control path
CONFIG_ESP_HOSTED_HOST_FEAT_RPC_EXT_V2=y       # required RPC ext-v2

Then build and run:

eh.py build
eh.py run

Python app — same RPC surface, driven from main/main.py:

cd examples/gpio_expander/linux_802_3_host/py_app
eh.py set-target linux
eh.py build
eh.py run

3. Verify

  • Each demo step toggles the same CP pin through every mode supported by the gpio_exp feature: input, input-pullup, output, open-drain.

  • The Linux variants exercise exactly the same RPC surface from user-space C, kernel-space, and Python.

MCU MCU Host Setup

1. Coprocessor

Set up the tools once (from the repo root):

cd /path/to/esp_hosted
./install.sh      # install.fish for the fish shell
. ./export.sh     # . ./export.fish for the fish shell

GPIO-expander support is enabled by the co-processor's sdkconfig.defaults (ESP_HOSTED_CP_FEAT_GPIO_EXP) — no extra option to enable. Select the transport via eh.py menuconfig:

cd examples/gpio_expander/cp
eh.py set-target esp32c6
eh.py menuconfig
Component config
└── ESP-Hosted
     └── Configure coprocessor
          └── CP transport
               ├── Communication bus (co-processor <== bus ==> host)
               │    ├── ( ) SPI Full Duplex
               │    ├── (X) SDIO                    <── default
               │    ├── ( ) SPI Half Duplex         ← MCU host only
               │    └── ( ) UART                    ← MCU host only
               └── SDIO Configuration               ← clock, GPIOs, checksum (defaults OK)

The CP-side pin under test (default GPIO 2) is set in code via SLAVE_GPIO_PIN. Each bus has its own settings submenu (pins, clock, checksum) — defaults are fine for bring-up.

The CP dependency config is pre-set in sdkconfig.defaults (do not remove):

CONFIG_ESP_HOSTED_CP_FEAT_GPIO_EXP=y           # CP GPIO-expander feature
CONFIG_BT_ENABLED=n                            # BT off (unused by this example)

Then flash and monitor:

eh.py -p <cp_usb_serial_port> flash monitor

2. MCU Host

Set up the tools once (from the repo root):

cd /path/to/esp_hosted
./install.sh      # install.fish for the fish shell
. ./export.sh     # . ./export.fish for the fish shell

Select the transport (must match the co-processor):

cd examples/gpio_expander/mcu_host
eh.py set-target esp32p4
eh.py menuconfig
Component config
└── ESP-Hosted
     └── Configure host
          └── Host transport
               ├── Communication bus (co-processor <== bus ==> host)
               │    ├── ( ) SPI Full Duplex
               │    ├── (X) SDIO                    <── default (match the co-processor)
               │    ├── ( ) SPI Half Duplex
               │    └── ( ) UART
               └── SDIO Configuration               ← slot, bus width, GPIOs (defaults OK)

The host GPIO-expander feature is enabled by sdkconfig.defaults (ESP_HOSTED_HOST_FEAT_GPIO_EXP); this host has no example-specific menu. The CP-side pin under test (default GPIO 2) is set in code via SLAVE_GPIO_PIN.

The Host dependency config is pre-set in sdkconfig.defaults (do not remove):

CONFIG_ESP_HOSTED_HOST_FEAT_GPIO_EXP=y         # host GPIO-expander feature
CONFIG_ESP_HOSTED_HOST_FEAT_RPC=y              # RPC control path
CONFIG_ESP_HOSTED_HOST_FEAT_RPC_EXT_V2=y       # required RPC ext-v2
CONFIG_ESP_HOSTED_HOST_FEAT_SYSTEM=y           # system RPC calls

Then flash and monitor:

eh.py -p <host_usb_serial_port> flash monitor

3. Verify

  • Each demo step toggles the same CP pin through every mode supported by the gpio_exp feature: input, input-pullup, output, open-drain.

  • The Linux variants exercise exactly the same RPC surface from user-space C, kernel-space, and Python.