d5e9ab6e61
machine.time_pulse_us() is intended to provide very fine timing, including while working with signal bursts, where each transition is tracked in row. Throwing and handling an exception may take too much time and "signal loss". So instead, in case of a timeout, just return negative value. Cases of timeout while waiting for initial signal stabilization, and during actual timing, are recognized. The documentation is updated accordingly, and rewritten somewhat to clarify the function behavior.
171 lines
5.3 KiB
ReStructuredText
171 lines
5.3 KiB
ReStructuredText
:mod:`machine` --- functions related to the hardware
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====================================================
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.. module:: machine
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:synopsis: functions related to the hardware
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The ``machine`` module contains specific functions related to the hardware
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on a particular board. Most functions in this module allow to achieve direct
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and unrestricted access to and control of hardware blocks on a system
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(like CPU, timers, buses, etc.). Used incorrectly, this can lead to
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malfunction, lockups, crashes of your board, and in extreme cases, hardware
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damage.
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.. _machine_callbacks:
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A note of callbacks used by functions and class methods of ``machine`` module:
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all these callbacks should be considered as executing in an interrupt context.
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This is true for both physical devices with IDs >= 0 and "virtual" devices
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with negative IDs like -1 (these "virtual" devices are still thin shims on
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top of real hardware and real hardware intrerrupts). See :ref:`isr_rules`.
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Reset related functions
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-----------------------
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.. function:: reset()
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Resets the device in a manner similar to pushing the external RESET
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button.
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.. function:: reset_cause()
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Get the reset cause. See :ref:`constants <machine_constants>` for the possible return values.
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Interrupt related functions
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---------------------------
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.. function:: disable_irq()
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Disable interrupt requests.
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Returns the previous IRQ state which should be considered an opaque value.
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This return value should be passed to the ``enable_irq`` function to restore
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interrupts to their original state, before ``disable_irq`` was called.
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.. function:: enable_irq(state)
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Re-enable interrupt requests.
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The ``state`` parameter should be the value that was returned from the most
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recent call to the ``disable_irq`` function.
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Power related functions
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-----------------------
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.. function:: freq()
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.. only:: not port_wipy
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Returns CPU frequency in hertz.
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.. only:: port_wipy
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Returns a tuple of clock frequencies: ``(sysclk,)``
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These correspond to:
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- sysclk: frequency of the CPU
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.. function:: idle()
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Gates the clock to the CPU, useful to reduce power consumption at any time during
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short or long periods. Peripherals continue working and execution resumes as soon
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as any interrupt is triggered (on many ports this includes system timer
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interrupt occurring at regular intervals on the order of millisecond).
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.. function:: sleep()
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Stops the CPU and disables all peripherals except for WLAN. Execution is resumed from
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the point where the sleep was requested. For wake up to actually happen, wake sources
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should be configured first.
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.. function:: deepsleep()
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Stops the CPU and all peripherals (including networking interfaces, if any). Execution
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is resumed from the main script, just as with a reset. The reset cause can be checked
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to know that we are coming from ``machine.DEEPSLEEP``. For wake up to actually happen,
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wake sources should be configured first, like ``Pin`` change or ``RTC`` timeout.
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.. only:: port_wipy
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.. function:: wake_reason()
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Get the wake reason. See :ref:`constants <machine_constants>` for the possible return values.
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Miscellaneous functions
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-----------------------
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.. only:: port_wipy
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.. function:: main(filename)
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Set the filename of the main script to run after boot.py is finished. If
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this function is not called then the default file main.py will be executed.
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It only makes sense to call this function from within boot.py.
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.. function:: rng()
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Return a 24-bit software generated random number.
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.. function:: unique_id()
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Returns a byte string with a unique identifier of a board/SoC. It will vary
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from a board/SoC instance to another, if underlying hardware allows. Length
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varies by hardware (so use substring of a full value if you expect a short
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ID). In some MicroPython ports, ID corresponds to the network MAC address.
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.. function:: time_pulse_us(pin, pulse_level, timeout_us=1000000)
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Time a pulse on the given `pin`, and return the duration of the pulse in
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microseconds. The `pulse_level` argument should be 0 to time a low pulse
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or 1 to time a high pulse.
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If the current input value of the pin is different to `pulse_level`,
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the function first (*) waits until the pin input becomes equal to `pulse_level`,
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then (**) times the duration that the pin is equal to `pulse_level`.
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If the pin is already equal to `pulse_level` then timing starts straight away.
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The function will return -2 if there was timeout waiting for condition marked
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(*) above, and -1 if there was timeout during the main measurement, marked (**)
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above. The timeout is the same for both cases and given by `timeout_us` (which
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is in microseconds).
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.. _machine_constants:
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Constants
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---------
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.. data:: machine.IDLE
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.. data:: machine.SLEEP
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.. data:: machine.DEEPSLEEP
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irq wake values
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.. data:: machine.PWRON_RESET
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.. data:: machine.HARD_RESET
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.. data:: machine.WDT_RESET
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.. data:: machine.DEEPSLEEP_RESET
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.. data:: machine.SOFT_RESET
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reset causes
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.. data:: machine.WLAN_WAKE
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.. data:: machine.PIN_WAKE
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.. data:: machine.RTC_WAKE
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wake reasons
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Classes
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-------
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.. toctree::
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:maxdepth: 1
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machine.ADC.rst
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machine.I2C.rst
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machine.Pin.rst
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machine.RTC.rst
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machine.SD.rst
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machine.SPI.rst
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machine.Timer.rst
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machine.UART.rst
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machine.WDT.rst
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