make IRQ example work on Linux

Author: 2bndy5

docs/index.rst

@@ -172,7 +172,7 @@ to the MCU via a digital input pin during the interrupt example.
     SCK, SCK, "GPIO11 (SCK)"
     MOSI, MOSI, "GPIO10 (MOSI)"
     MISO, MISO, "GPIO9 (MISO)"
-    IRQ, D12, GPIO12
+    IRQ, D12, GPIO24
 
 .. tip::
     User reports and personal experiences have improved results if there is a capacitor of

examples/nrf24l01_interrupt_test.py

@@ -7,22 +7,35 @@
 
 import time
 import board
-import digitalio
+from digitalio import DigitalInOut
 
 # if running this on a ATSAMD21 M0 based board
 # from circuitpython_nrf24l01.rf24_lite import RF24
 from circuitpython_nrf24l01.rf24 import RF24
 
-# select your digital input pin that's connected to the IRQ pin on the nRF4L01
-irq_pin = digitalio.DigitalInOut(board.D12)
-irq_pin.switch_to_input()  # make sure its an input object
-# change these (digital output) pins accordingly
-CE_PIN = digitalio.DigitalInOut(board.D4)
-CSN_PIN = digitalio.DigitalInOut(board.D5)
+# invalid default values for scoping
+SPI_BUS, CSN_PIN, CE_PIN = (None, None, None)
+
+try:  # on Linux
+    import spidev
+
+    SPI_BUS = spidev.SpiDev()  # for a faster interface on linux
+    CSN_PIN = 0  # use CE0 on default bus (even faster than using any pin)
+    CE_PIN = DigitalInOut(board.D22)  # using pin gpio22 (BCM numbering)
+    IRQ_PIN = DigitalInOut(board.D24)  # using gpio24 (BCM numbering)
 
-# using board.SPI() automatically selects the MCU's
-# available SPI pins, board.SCK, board.MOSI, board.MISO
-SPI_BUS = board.SPI()  # init spi bus object
+except ImportError:  # on CircuitPython only
+    # using board.SPI() automatically selects the MCU's
+    # available SPI pins, board.SCK, board.MOSI, board.MISO
+    SPI_BUS = board.SPI()  # init spi bus object
+
+    # change these (GPIO) pins accordingly
+    CE_PIN = DigitalInOut(board.D4)
+    CSN_PIN = DigitalInOut(board.D5)
+    IRQ_PIN = DigitalInOut(board.D12)
+
+# select your digital input pin that's connected to the IRQ pin on the nRF4L01
+IRQ_PIN.switch_to_input()  # make sure its an input object
 
 # we'll be using the dynamic payload size feature (enabled by default)
 # initialize the nRF24L01 on the spi bus object
@@ -59,7 +72,7 @@ def _ping_and_prompt():
     nrf.ce_pin = 1  # tell the nRF24L01 to prepare sending a single packet
     time.sleep(0.00001)  # mandatory 10 microsecond pulse starts transmission
     nrf.ce_pin = 0  # end 10 us pulse; use only 1 buffer from TX FIFO
-    while irq_pin.value:  # IRQ pin is active when LOW
+    while IRQ_PIN.value:  # IRQ pin is active when LOW
         pass
     print("IRQ pin went active LOW.")
     nrf.update()  # update irq_d? status flags