96 lines
5.2 KiB
ReStructuredText
96 lines
5.2 KiB
ReStructuredText
Pulse Counter
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=============
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Introduction
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------------
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The PCNT (Pulse Counter) module is designed to count the number of rising and/or falling edges of an input signal. Each pulse counter unit has a 16-bit signed counter register and two channels that can be configured to either increment or decrement the counter. Each channel has a signal input that accepts signal edges to be detected, as well as a control input that can be used to enable or disable the signal input. The inputs have optional filters that can be used to discard unwanted glitches in the signal.
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Functionality Overview
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----------------------
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Description of functionality of this API has been broken down into four sections:
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* :ref:`pcnt-api-configuration` - describes counter's configuration parameters and how to setup the counter.
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* :ref:`pcnt-api-operating-the-counter` - provides information on control functions to pause, measure and clear the counter.
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* :ref:`pcnt-api-filtering-pulses` - describes options to filtering pulses and the counter control signals.
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* :ref:`pcnt-api-using-interrupts` - presents how to trigger interrupts on specific states of the counter.
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.. _pcnt-api-configuration:
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Configuration
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-------------
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The PCNT module has eight independent counting "units" numbered from 0 to 7. In the API they are referred to using :cpp:type:`pcnt_unit_t`. Each unit has two independent channels numbered as 0 and 1 and specified with :cpp:type:`pcnt_channel_t`.
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The configuration is provided separately per unit's channel using :cpp:type:`pcnt_config_t` and covers:
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* The unit and the channel number this configuration refers to.
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* GPIO numbers of the pulse input and the pulse gate input.
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* Two pairs of parameters: :cpp:type:`pcnt_ctrl_mode_t` and :cpp:type:`pcnt_count_mode_t` to define how the counter reacts depending on the the status of control signal and how counting is done positive / negative edge of the pulses.
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* Two limit values (minimum / maximum) that are used to establish watchpoints and trigger interrupts when the pulse count is meeting particular limit.
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Setting up of particular channel is then done by calling a function :cpp:func:`pcnt_unit_config` with above :cpp:type:`pcnt_config_t` as the input parameter.
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To disable the pulse or the control input pin in configuration, provide :cpp:type:`PCNT_PIN_NOT_USED` instead of the GPIO number.
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.. _pcnt-api-operating-the-counter:
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Operating the Counter
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---------------------
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After doing setup with :cpp:func:`pcnt_unit_config`, the counter immediately starts to operate. The accumulated pulse count can be checked by calling :cpp:func:`pcnt_get_counter_value`.
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There are couple of functions that allow to control the counter's operation: :cpp:func:`pcnt_counter_pause`, :cpp:func:`pcnt_counter_resume` and :cpp:func:`pcnt_counter_clear`
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It is also possible to dynamically change the previously set up counter modes with :cpp:func:`pcnt_unit_config` by calling :cpp:func:`pcnt_set_mode`.
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If desired, the pulse input pin and the control input pin may be changed "on the fly" using :cpp:func:`pcnt_set_pin`. To disable particular input provide as a function parameter :cpp:type:`PCNT_PIN_NOT_USED` instead of the GPIO number.
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.. note::
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For the counter not to miss any pulses, the pulse duration should be longer than one APB_CLK cycle (12.5 ns). The pulses are sampled on the edges of the APB_CLK clock and may be missed, if fall between the edges. This applies to counter operation with or without a :ref:`filer <pcnt-api-filtering-pulses>`.
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.. _pcnt-api-filtering-pulses:
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Filtering Pulses
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----------------
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The PCNT unit features filters on each of the pulse and control inputs, adding the option to ignore short glitches in the signals.
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The length of ignored pulses is provided in APB_CLK clock cycles by calling :cpp:func:`pcnt_set_filter_value`. The current filter setting may be checked with :cpp:func:`pcnt_get_filter_value`. The APB_CLK clock is running at 80 MHz.
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The filter is put into operation / suspended by calling :cpp:func:`pcnt_filter_enable` / :cpp:func:`pcnt_filter_disable`.
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.. _pcnt-api-using-interrupts:
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Using Interrupts
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----------------
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There are five counter state watch events, defined in :cpp:type:`pcnt_evt_type_t`, that are able to trigger an interrupt. The event happens on the pulse counter reaching specific values:
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* Minimum or maximum count values: :cpp:member:`counter_l_lim` or :cpp:member:`counter_h_lim` provided in :cpp:type:`pcnt_config_t` as discussed in :ref:`pcnt-api-configuration`
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* Threshold 0 or Threshold 1 values set using function :cpp:func:`pcnt_set_event_value`.
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* Pulse count = 0
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To register, enable or disable an interrupt to service the above events, call :cpp:func:`pcnt_isr_register`, :cpp:func:`pcnt_intr_enable`. and :cpp:func:`pcnt_intr_disable`. To enable or disable events on reaching threshold values, you will also need to call functions :cpp:func:`pcnt_event_enable` and :cpp:func:`pcnt_event_disable`.
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In order to check what are the threshold values currently set, use function :cpp:func:`pcnt_get_event_value`.
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Application Example
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-------------------
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Pulse counter with control signal and event interrupt example: :example:`peripherals/pcnt`.
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API Reference
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-------------
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.. include:: /_build/inc/pcnt.inc
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