class Counter – pulse counter
Counter implements pulse counting by monitoring an input signal and counting rising or falling edges.
Minimal ESP32 example usage:
from machine import Pin, Counter
counter = Counter(0, Pin(0, Pin.IN)) # create Counter for pin 0 and begin counting
value = counter.value() # retrieve current pulse count
Availability: ESP32, MIMXRT
Constructors
- class machine.Counter(id, ...)
Returns the singleton Counter object for the the given id. Values of id depend on a particular port and its hardware. Values 0, 1, etc. are commonly used to select hardware block #0, #1, etc.
Additional arguments are passed to the
init()method described below, and will cause the Counter instance to be re-initialised and reset.On ESP32, the id corresponds to a PCNT unit.
Methods
- Counter.init(src, *, ...)
Initialise and reset the Counter with the given parameters:
src specifies the input pin as a machine.Pin object. May be omitted on ports that have a predefined pin for a given hardware block.
Additional keyword-only parameters that may be supported by a port are:
edge specifies the edge to count. Either
Counter.RISING(the default) orCounter.FALLING. (Supported on ESP32)direction specifies the direction to count. Either
Counter.UP(the default) orCounter.DOWN. (Supported on ESP32 and MIMXRT) A machine.Pin object as parameter argument specifies a pin which controls the counting direction. Low: Count up, High: Count down. (Supported on MIMXRT)filter_ns specifies a minimum period of time in nanoseconds that the source signal needs to be stable for a pulse to be counted. Implementations should use the longest filter supported by the hardware that is less than or equal to this value. The default is 0 (no filter). (Supported on ESP32 and MIMXRT)
max Specify the upper counting range. The position counter will count up from a min start value up to max, then roll over to the init value and increase the cycles counter by one. When counting down, the cycles counter decreases at the transition from min to max. The range is reset by defining both max and min to 0. The default value is the hardware’s counter range. (Supported by MIMXRT and the ESP32 PCNT module)
min Specify the lower counting range. The default value is 0. (Supported by MIMXRT and the ESP32 PCNT module)
index A Pin specifier telling to which pin the index pulse is connected. At a rising slope of the index pulse the pulse counter is reset to the min value and the cycles counter is increased or decreased by one, depending on the counting direction. A value of None disables the index input. (Supported on MIMXRT)
reset A Pin specifier telling to which pin the reset pulse is connected. At a rising slope of the reset pulse the counter is set to the init value, but the cycles counter is not changed. A value of None disables the reset input. (Supported on MIMXRT)
match Set the counter value at which the interrupt IRQ_MATCH shall trigger. The value is not checked for being in the bounds of the counter range. This option if equivalent to the threshold options of the ESP32 PCNT module. A value of None resets the match value and disables the IRQ_MATCH interrupt. (Supported on MIMXRT)
match_pin A Pin specifier telling to which pin the match output is connected. This output will have a high level as long as the counter matches the match value. The signal is generated by the encoder logic and requires no further software support. The pulse width is defined by the input signal frequency and can be very short, like 20ns, or stay, if the counter stops at the match value. A value of None disables the match output. (Supported on MIMXRT)
- Counter.deinit()
Stops the Counter, disabling any interrupts and releasing hardware resources. A Soft Reset should deinitialize all Counter objects.
- Counter.value([value])
Get, and optionally set, the counter value as a signed integer. Implementations must aim to do the get and set atomically (i.e. without leading to skipped counts).
This counter value could exceed the range of a small integer, which means that calling
Counter.value()could cause a heap allocation, but implementations should aim to ensure that internal state only uses small integers and therefore will not allocate until the user callsCounter.value().For example, on ESP32, the internal state counts overflows of the hardware counter (every 32000 counts), which means that it will not exceed the small integer range until
2**30 * 32000counts (slightly over 1 year at 1MHz).In general, it is recommended that you should use
Counter.value(0)to reset the counter (i.e. to measure the counts since the last call), and this will avoid this problem.
- Counter.cycles([value])
Get or set the current cycles counter of the counter as signed 16 bit integer. The value represents the overflow or underflow events of the count range. With no arguments the actual cycles counter value is returned. With a single value argument the cycles counter is set to that value. The base counter is not changed. The method returns the previous value. (Supported on MIMXRT)
- Counter.irq(handler=None, trigger=0, hard=False)
Specifies, that the handler is called when the respective event happens.
- event may be:
Counter.IRQ_RESET Triggered with a transition at the reset input.
Counter.IRQ_INDEX Triggered with a transition at the index input.
Counter.IRQ_MATCH Triggered when the positions counter matches the match value. For fast signals, the actual position counter value when retrieved in the callback may be different from the trigger value.
Counter.IRQ_ROLL_OVER Triggered when the position counter rolls over from the highest to the lowest value.
Counter.IRQ_ROLL_UNDER Triggered when the position counter rolls under from the lowest to the highest value.
The callback function handler receives a single argument, which is the Counter object. All events share the same callback. The event which triggers the callback can be identified with the irq.flags() method. The argument hard specifies, whether the callback is called as a hard interrupt or as regular scheduled function. Hard interrupts have always a short latency, but are limited in that they must not allocate memory. Regular scheduled functions are not limited in what can be used, but depending on the load of the device execution may be delayed. Under low load, the difference in latency is minor.
The default arguments values are handler=None, trigger=0, hard=False. The callback will be disabled, when called with handler=None.
The position match event is triggered as long as the position and match value are identical. Therefore the position match callback is run in a one-shot fashion, and has to be enabled again when the position has changed. It will be enabled by re-defining the trigger with either
Counter.irq()orirq().trigger(). For ESP32, Counter interrupts are handled by the PCNT. (Supported on MIMXRT)