Documentation: update capture.rst with notification and fake driver

These documentation updates correspond to commits:
- drivers/capture: add signal notification support for edge capture events
- drivers/capture: add fake capture driver for testing and development

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

Author: Donny9

Documentation/components/drivers/character/timers/capture.rst

@@ -72,17 +72,58 @@ Supported ``ioctl`` Commands
 
    **Argument:** ``int`` (value to watch for).
 
+.. c:macro:: CAPIOC_REGISTER
+
+   Register for capture edge event notifications. This allows applications
+   to receive asynchronous signal notifications when capture edge events
+   occur, instead of polling for events.
+
+   **Argument:** ``struct cap_notify_s *`` (pointer to notification structure).
+
+   The ``struct cap_notify_s`` contains:
+
+   * ``event`` - The signal event configuration (``struct sigevent``)
+   * ``chan`` - Capture channel number
+   * ``type`` - Edge type (``CAP_TYPE_RISING``, ``CAP_TYPE_FALLING``, or ``CAP_TYPE_BOTH``)
+   * ``ptr`` - User data pointer
+
+   **Returns:**
+
+   * ``OK`` on success
+   * ``-EINVAL`` for invalid channel
+   * ``-EBUSY`` if channel already registered by another task
+
+.. c:macro:: CAPIOC_UNREGISTER
+
+   Unregister capture edge event notifications.
+
+   **Argument:** ``int`` (channel number).
+
+   **Returns:** ``OK`` on success.
+
 Configuration
 -------------
 
 To enable the capture driver, enable the following configuration options:
 
-* ``CONFIG_CAPTURE``
-* ``CONFIG_STM32H7_TIM4_CAP`` (for STM32H7 Timer 4)
+* ``CONFIG_CAPTURE`` - Enable the capture driver framework
+* ``CONFIG_CAPTURE_NOTIFY`` - Enable signal notification support for edge events
+* ``CONFIG_FAKE_CAPTURE`` - Enable fake capture driver for testing (generates 10Hz signal with 50% duty cycle)
+* ``CONFIG_STM32H7_TIM4_CAP`` (for STM32H7 Timer 4, platform-specific)
 
 The ``CONFIG_CAPTURE`` option enables the lower-half driver and registers
 the ``/dev/capture`` device.
 
+The ``CONFIG_CAPTURE_NOTIFY`` option enables the signal notification feature,
+allowing applications to receive asynchronous notifications when capture
+edge events occur. This requires hardware support for edge interrupts and
+depends on ``CONFIG_CAPTURE``.
+
+The ``CONFIG_FAKE_CAPTURE`` option enables a software-based fake capture
+driver that simulates a 10Hz square wave with 50% duty cycle. This is
+useful for development and testing without requiring actual hardware.
+It depends on ``CONFIG_CAPTURE`` and ``CONFIG_CAPTURE_NSIGNALS > 0``.
+
 Without it, capture is still possible manually by including the appropriate
 header (e.g., ``arch/arm/src/stm32h7/stm32_capture.h``) and performing a
 manual initialization.
@@ -125,6 +166,129 @@ frequency:
       return 0;
     }
 
+Signal Notification Example
+----------------------------
+
+Here is an example using signal notifications for event-driven capture
+(requires ``CONFIG_CAPTURE_NOTIFY``):
+
+.. code-block:: c
+
+    #include <stdio.h>
+    #include <signal.h>
+    #include <fcntl.h>
+    #include <sys/ioctl.h>
+    #include <nuttx/timers/capture.h>
+
+    static volatile int edge_count = 0;
+
+    static void capture_handler(int signo, siginfo_t *info, void *context)
+    {
+      edge_count++;
+    }
+
+    int main(int argc, char *argv[])
+    {
+      int fd;
+      struct cap_notify_s notify;
+      struct sigaction sa;
+      uint32_t frequency;
+      uint8_t duty;
+
+      /* Set up signal handler */
+      sa.sa_sigaction = capture_handler;
+      sa.sa_flags = SA_SIGINFO;
+      sigemptyset(&sa.sa_mask);
+      sigaction(SIGUSR1, &sa, NULL);
+
+      /* Open capture device */
+      fd = open("/dev/capture0", O_RDONLY);
+      if (fd < 0)
+        {
+          perror("Failed to open capture device");
+          return 1;
+        }
+
+      /* Configure notification for both edges on channel 0 */
+      notify.chan = 0;
+      notify.type = CAP_TYPE_BOTH;
+      notify.event.sigev_notify = SIGEV_SIGNAL;
+      notify.event.sigev_signo = SIGUSR1;
+      notify.event.sigev_value.sival_ptr = NULL;
+
+      if (ioctl(fd, CAPIOC_REGISTER, (unsigned long)&notify) < 0)
+        {
+          perror("Failed to register notification");
+          close(fd);
+          return 1;
+        }
+
+      printf("Waiting for capture events...\n");
+
+      /* Wait for some events */
+      sleep(2);
+
+      /* Get frequency and duty cycle */
+      ioctl(fd, CAPIOC_FREQUENCE, (unsigned long)&frequency);
+      ioctl(fd, CAPIOC_DUTYCYCLE, (unsigned long)&duty);
+
+      printf("Captured %d edges\n", edge_count);
+      printf("Frequency: %u Hz, Duty: %u%%\n", frequency, duty);
+
+      /* Unregister notification */
+      ioctl(fd, CAPIOC_UNREGISTER, 0);
+
+      close(fd);
+      return 0;
+    }
+
+Fake Capture Testing Example
+-----------------------------
+
+The fake capture driver can be used for testing without hardware
+(requires ``CONFIG_FAKE_CAPTURE``):
+
+.. code-block:: c
+
+    #include <stdio.h>
+    #include <fcntl.h>
+    #include <sys/ioctl.h>
+    #include <nuttx/timers/capture.h>
+
+    int main(int argc, char *argv[])
+    {
+      int fd;
+      uint32_t frequency;
+      uint8_t duty;
+
+      /* Open fake capture device */
+      fd = open("/dev/fake_capture0", O_RDONLY);
+      if (fd < 0)
+        {
+          perror("Failed to open fake capture device");
+          return 1;
+        }
+
+      /* Start capture */
+      ioctl(fd, CAPIOC_START, 0);
+
+      /* Wait for capture to stabilize */
+      sleep(1);
+
+      /* Read values (should be 10Hz, 50% duty) */
+      ioctl(fd, CAPIOC_FREQUENCE, (unsigned long)&frequency);
+      ioctl(fd, CAPIOC_DUTYCYCLE, (unsigned long)&duty);
+
+      printf("Fake Capture - Frequency: %u Hz, Duty: %u%%\n",
+             frequency, duty);
+
+      /* Stop capture */
+      ioctl(fd, CAPIOC_STOP, 0);
+
+      close(fd);
+      return 0;
+    }
+
 Notes
 -----
 
@@ -136,3 +300,38 @@ Notes
 * **Important:** In debug builds of NuttX, calling an unsupported
   ``ioctl`` command will trigger a ``DEBUGASSERT`` in the driver,
   which will halt or crash the system.
+
+Signal Notification Features
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When ``CONFIG_CAPTURE_NOTIFY`` is enabled:
+
+* Applications can register for asynchronous edge event notifications
+* Supports per-channel registration with independent configurations
+* Edge types supported: rising edge (``CAP_TYPE_RISING``), falling edge
+  (``CAP_TYPE_FALLING``), or both (``CAP_TYPE_BOTH``)
+* Only one task can register per channel at a time
+* Signal notifications use standard POSIX ``sigevent`` mechanism
+* Lower-half drivers must implement ``bind()`` and ``unbind()`` operations
+* Ideal for event-driven applications like tachometers, encoders, and
+  frequency counters
+
+Fake Capture Driver
+~~~~~~~~~~~~~~~~~~~
+
+The fake capture driver (``CONFIG_FAKE_CAPTURE``) provides:
+
+* Software simulation of capture events using watchdog timers
+* Fixed 10Hz frequency with 50% duty cycle
+* Edge toggles every 50ms (rising and falling)
+* Supports all standard capture operations including notifications
+* Available at ``/dev/fake_capture0``, ``/dev/fake_capture1``, etc.
+* Useful for development, testing, and CI/CD without hardware
+* Platform-independent implementation
+* Automatically initialized at boot (2 channels by default)
+
+Limitations:
+
+* Fixed timing parameters (not configurable at runtime)
+* Software timing accuracy (not hardware-precise)
+* Suitable for functional testing, not timing precision validation