linguini1 commented on code in PR #18951:
URL: https://github.com/apache/nuttx/pull/18951#discussion_r3295227555
##########
Documentation/platforms/sim/sim_ft2232h_gpio.rst:
##########
@@ -0,0 +1,218 @@
+=======================================
+Sim FT2232 GPIO Driver (Using libftdi1)
+=======================================
+
+Overview
+========
+
+The NuttX simulation (sim) already has a GPIO Chip driver that provides a
mechanism use GPIO to control external devices. However that solution depends
on having a driver to Linux side and that adds more overhead.
+
+This FT2232H driver allows a direct use of libftdi1 to control up to 8 GPIOs.
+
+This driver is particularly useful for:
+
+- Testing GPIO-based applications in a simulated environment with real hardware
+- Interfacing with USB-to-GPIO adapters from NuttX simulation
+- Developing and debugging GPIO drivers without dedicated embedded hardware
+
+Host Prepare
+============
+
+Preparation required on the host side:
+
+- Hardware module required: FT2232H module like the CJMCU-2232HL module
+- A udev rule on Linux side to avoid using the FT2232H as USB/Serial:
+
+.. code-block:: console
+
+ $ cat /etc/udev/rules.d/99-ft2232h-d2xx.rules
+ ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6010", ATTRS{product}=="FTDI
Device", MODE="0666"
+
+- The libftdi1-dev installed on your system.
+
+Architecture
+============
+
+The driver consists of two layers:
+
+1. **NuttX Layer** (``sim_ft2232h_ioexpander.c``): Implements the NuttX
``ioexpander_dev_s``
+ interface, providing standard GPIO operations to upper-layer NuttX drivers.
+
+2. **Host Layer** (``sim_ft2232h.c``): Interfaces directly with libftdio1 to
initialize and to provide the functions to control the GPIOs.
+
+::
+
+ +---------------------+
+ | NuttX Application |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | GPIO Lower Half |
+ | (gpio_lower_half) |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | sim_ft2232h_ioex...c| <-- NuttX ioexpander interface
+ | (ioexpander_dev_s) |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | sim_ft2232h.c | <-- Linux host GPIO interface
+ | (host interface) |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | libftdi1 | <-- Linux library to control FT2232H
+ +---------------------+
+
+Header Files
+============
+
+- ``arch/sim/src/sim/sim_ft2232h_ioexpander.h``: Host GPIO chip interface
definitions and function prototypes.
+
+- ``include/nuttx/ioexpander/ioexpander.h``: Standard NuttX IO expander
interface.
+
+- ``include/nuttx/ioexpander/gpio.h``: NuttX GPIO interface definitions.
+
+Configuration Options
+=====================
+
+The following configuration options are relevant to this driver:
+
+- ``CONFIG_SIM_FT2232H``: Enable the FT2232H driver support.
+- ``CONFIG_SIM_FT2232H_GPIO``: Enable the sim GPIO chip driver.
+
+Supported Operations
+====================
+
+The driver supports the following GPIO operations:
+
+Direction Control
+-----------------
+
+.. code-block:: c
+
+ int sim_ft2232h_gpio_direction(struct ioexpander_dev_s *dev,
+ uint8_t pin, int direction);
+
+Set GPIO pin direction. Supported directions:
+
+- ``IOEXPANDER_DIRECTION_IN``: Configure as input
+- ``IOEXPANDER_DIRECTION_OUT``: Configure as output
+- ``IOEXPANDER_DIRECTION_OUT_OPENDRAIN``: Configure as open-drain output
+
+Read/Write Pin
+--------------
+
+.. code-block:: c
+
+ int sim_ft2232h_gpio_readpin(struct ioexpander_dev_s *dev, uint8_t pin,
+ bool *value);
+ int sim_ft2232h_gpio_writepin(struct ioexpander_dev_s *dev, uint8_t pin,
+ bool value);
+
+Read or write the value of a GPIO pin.
+
+Host Layer API
+==============
+
+The host layer (``sim_ft2232h.c``) provides the following functions:
+
+.. code-block:: c
+
+ /* Allocate and initialize a host GPIO chip device */
+ struct host_ft2232h_gpio_dev *host_ft2232h_gpio_alloc(const char *filename);
+
+ /* Free a host GPIO chip device */
+ void host_ft2232h_gpio_free(struct host_ft2232h_gpio_dev *dev);
+
+ /* Set GPIO pin direction */
+ int host_ft2232h_gpio_direction(struct host_ft2232h_gpio_dev *dev,
+ uint8_t pin, bool input);
+
+ /* Read GPIO pin value */
+ int host_ft2232h_gpio_readpin(struct host_ft2232h_gpio_dev *dev,
+ uint8_t pin, bool *value);
+
+ /* Write GPIO pin value */
+ int host_ft2232h_gpio_writepin(struct host_ft2232h_gpio_dev *dev,
+ uint8_t pin, bool value);
+
+ /* Request GPIO interrupt */
+ int host_ft2232h_gpio_irq_request(struct host_ft2232h_gpio_dev *dev,
+ uint8_t pin, uint16_t cfgset);
+
+ /* Check if GPIO interrupt is active */
+ bool host_ft2232h_gpio_irq_active(struct host_ft2232h_gpio_dev *dev,
uint8_t pin);
+
+ /* Get GPIO line information */
+ int host_ft2232h_gpio_get_line(struct host_ft2232h_gpio_dev *priv,
+ uint8_t pin, bool *input);
+
+Linux Kernel Version Requirements
+=================================
+
+The driver uses Linux GPIO v2 ABI, which requires:
+
+- **Linux kernel >= 6.8.0**: Full functionality with GPIO v2 API support.
+- **Linux kernel < 6.8.0**: The driver compiles but provides stub
implementations
+ that return 0 or NULL.
+
+Usage Example
+=============
+
+Initialization
+--------------
+
+Application Usage
+-----------------
+
+After initialization, GPIO pins can be accessed through standard NuttX GPIO
interface:
+
+.. code-block:: c
+
+ #include <fcntl.h>
+ #include <sys/ioctl.h>
+ #include <nuttx/ioexpander/gpio.h>
+
+ int main(void)
+ {
+ int fd;
+ bool value;
+
+ /* Open GPIO device */
+ fd = open("/dev/gpio20", O_RD);
+ if (fd < 0)
+ {
+ return -1;
+ }
+
+ /* Read GPIO value */
+ ioctl(fd, GPIOC_READ, &value);
+ printf("GPIO value: %d\n", value);
+
+ close(fd);
+ return 0;
+ }
+
+Files
+=====
+
+- ``arch/sim/src/sim/sim_ft2232h_ioexpander.c``: NuttX IO expander
implementation
+- ``arch/sim/src/sim/posix/sim_ft2232h.c``: Linux host GPIO interface
+- ``arch/sim/src/sim/sim_ft2232h_ioxpander.h``: Host GPIO chip header file
Review Comment:
Probably don't need to mention this.
##########
Documentation/platforms/sim/sim_ft2232h_gpio.rst:
##########
@@ -0,0 +1,218 @@
+=======================================
+Sim FT2232 GPIO Driver (Using libftdi1)
+=======================================
+
+Overview
+========
+
+The NuttX simulation (sim) already has a GPIO Chip driver that provides a
mechanism use GPIO to control external devices. However that solution depends
on having a driver to Linux side and that adds more overhead.
+
+This FT2232H driver allows a direct use of libftdi1 to control up to 8 GPIOs.
+
+This driver is particularly useful for:
+
+- Testing GPIO-based applications in a simulated environment with real hardware
+- Interfacing with USB-to-GPIO adapters from NuttX simulation
+- Developing and debugging GPIO drivers without dedicated embedded hardware
+
+Host Prepare
+============
+
+Preparation required on the host side:
+
+- Hardware module required: FT2232H module like the CJMCU-2232HL module
+- A udev rule on Linux side to avoid using the FT2232H as USB/Serial:
+
+.. code-block:: console
+
+ $ cat /etc/udev/rules.d/99-ft2232h-d2xx.rules
+ ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6010", ATTRS{product}=="FTDI
Device", MODE="0666"
+
+- The libftdi1-dev installed on your system.
+
+Architecture
+============
+
+The driver consists of two layers:
+
+1. **NuttX Layer** (``sim_ft2232h_ioexpander.c``): Implements the NuttX
``ioexpander_dev_s``
+ interface, providing standard GPIO operations to upper-layer NuttX drivers.
+
+2. **Host Layer** (``sim_ft2232h.c``): Interfaces directly with libftdio1 to
initialize and to provide the functions to control the GPIOs.
+
+::
+
+ +---------------------+
+ | NuttX Application |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | GPIO Lower Half |
+ | (gpio_lower_half) |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | sim_ft2232h_ioex...c| <-- NuttX ioexpander interface
+ | (ioexpander_dev_s) |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | sim_ft2232h.c | <-- Linux host GPIO interface
+ | (host interface) |
+ +---------------------+
+ |
+ v
+ +---------------------+
+ | libftdi1 | <-- Linux library to control FT2232H
+ +---------------------+
Review Comment:
You can use the plantuml plugin instead!
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