Documentation/drivers/timers: Add information about timers.

This commit added additional informantion about the timer driver
abstraction.

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

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

@@ -6,8 +6,31 @@ Timers Drivers
   :caption: Supported Drivers
 
   timer.rst
+  oneshot.rst
   pwm.rst
   watchdog.rst
   rtc.rst
   capture.rst
 
+The NuttX timing subsystem consists of four layers:
+
+  .. figure:: timer.svg
+
+  * 1 Hardware Timer Drivers: Includes implementations of various hardware
+                              timer drivers.
+  * 2 Timer Driver Abstraction: Such as Oneshot and Timer, which provide
+                                oneshot/periodical timer hardware abstraction.
+  * 3 OS Timer Interfaces: Arch_Timer(up_timer_*) and Arch_Alarm(up_alarm_*), 
+                           offering relative timer (trigger an event with a certain delay)
+                           and absolute timer (trigger an event at a certain time)
+                           interfaces.
+  * 4 OS Timer Abstraction: The wdog timer manages software timers
+                            and provides a unified timer API to upper layers.
+
+The Timer Driver Abstraction is not mandatory. If the driver is simple enough
+(e.g.,just providing a periodic tick), the OS Timer interfaces Arch_Timer
+can be implemented directly, bypassing the timer driver abstraction layer.
+
+The design purpose of the Timer Driver Abstraction is to simplify driver
+implementation, improve performance, and enhance the reusability of driver
+code.

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

@@ -7,10 +7,12 @@ The NuttX timing subsystem consists of four layers:
   * 1 Hardware Timer Drivers: Includes implementations of various hardware
                               timer drivers.
   * 2 Timer Driver Abstraction: Such as Oneshot and Timer, which provide
-                                timer hardware abstraction.
-  * 3 OS Timer Interfaces: Timer and Alarm, offering relative and
-                           absolute timer interfaces.
-  * 4 OS Timer Abstraction: The wdog (watchdog) module manages software timers
+                                oneshot/periodical timer hardware abstraction.
+  * 3 OS Timer Interfaces: Arch_Timer(up_timer_*) and Arch_Alarm(up_alarm_*), 
+                           offering relative timer (trigger an event with a certain delay)
+                           and absolute timer (trigger an event at a certain time)
+                           interfaces.
+  * 4 OS Timer Abstraction: The wdog timer manages software timers
                             and provides a unified timer API to upper layers.
 
 Here we focus on the oneshot timer driver abstraction.

Documentation/components/drivers/index.rst

@@ -12,7 +12,6 @@ divided in three classes:
   block/index.rst
   special/index.rst
   thermal/index.rst
-  timers/oneshot/index.rst
 
 .. note::
   Device driver support depends on the *in-memory*, *pseudo*