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Add note in documentation about behaviour of one-shot Hardware timer with Esp8266 #2713

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Jan 16, 2024
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Add note in documentation about behaviour of one-shot Hardware timer with Esp8266 #2713

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7 changes: 6 additions & 1 deletion Sming/Arch/Esp8266/Components/driver/include/driver/hw_timer.h
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Expand Up @@ -80,7 +80,12 @@ void IRAM_ATTR hw_timer1_attach_interrupt(hw_timer_source_type_t source_type, hw
* @brief Enable the timer
* @param div
* @param intr_type
* @param auto_load
* @param auto_load true for repeating timer, false for one-shot
*
* Note: With one-shot timer application callback must stop the timer when it is no longer required.
* This is to reduce callback latency.
* If this is not done, timer will trigger again when timer counter wraps around to 0.
* For /16 divisor this is only 1.7s.
*/
inline void IRAM_ATTR hw_timer1_enable(hw_timer_clkdiv_t div, hw_timer_intr_type_t intr_type, bool auto_load)
{
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14 changes: 14 additions & 0 deletions docs/source/framework/timers/hardware-timer.rst
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Expand Up @@ -11,5 +11,19 @@ The API for hardware (and :doc:`timer-queue` timers) is identical, implemented u
:cpp:class:`CallbackTimer` class template for best performance.


.. note::

**Applies to Esp8266 architecture only.**

As with all Callback timers, the :cpp:type:`HardwareTimer` can be one-shot or repeating.

With the Esp8266 a one-shot timer will repeat after it has been triggered, but only after the timer
counter wraps around. The Esp8266 only has 23 bits of resolution so with a clock divider of 16
this will happen after about 1.7s.

Because the Esp8266 lacks any proper PWM hardware the timer latency is critical.
Adding any additional code to the callback is therefore left to the programmer.


.. doxygengroup:: hardware_timer
:members:
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