105 lines
2.7 KiB
Python
105 lines
2.7 KiB
Python
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# Example using PIO to create a UART RX interface.
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#
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# To make it work you'll need a wire connecting GPIO4 and GPIO3.
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#
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# Demonstrates:
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# - PIO shifting in data on a pin
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# - PIO jmp(pin) instruction
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# - PIO irq handler
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# - using the second core via _thread
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import _thread
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from machine import Pin, UART
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from rp2 import PIO, StateMachine, asm_pio
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UART_BAUD = 9600
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HARD_UART_TX_PIN = Pin(4, Pin.OUT)
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PIO_RX_PIN = Pin(3, Pin.IN, Pin.PULL_UP)
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@asm_pio(
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autopush=True,
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push_thresh=8,
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in_shiftdir=rp2.PIO.SHIFT_RIGHT,
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)
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def uart_rx_mini():
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# fmt: off
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# Wait for start bit
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wait(0, pin, 0)
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# Preload bit counter, delay until eye of first data bit
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set(x, 7) [10]
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# Loop 8 times
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label("bitloop")
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# Sample data
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in_(pins, 1)
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# Each iteration is 8 cycles
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jmp(x_dec, "bitloop") [6]
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# fmt: on
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@asm_pio(
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in_shiftdir=rp2.PIO.SHIFT_RIGHT,
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)
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def uart_rx():
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# fmt: off
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label("start")
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# Stall until start bit is asserted
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wait(0, pin, 0)
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# Preload bit counter, then delay until halfway through
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# the first data bit (12 cycles incl wait, set).
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set(x, 7) [10]
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label("bitloop")
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# Shift data bit into ISR
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in_(pins, 1)
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# Loop 8 times, each loop iteration is 8 cycles
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jmp(x_dec, "bitloop") [6]
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# Check stop bit (should be high)
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jmp(pin, "good_stop")
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# Either a framing error or a break. Set a sticky flag
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# and wait for line to return to idle state.
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irq(block, 4)
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wait(1, pin, 0)
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# Don't push data if we didn't see good framing.
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jmp("start")
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# No delay before returning to start; a little slack is
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# important in case the TX clock is slightly too fast.
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label("good_stop")
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push(block)
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# fmt: on
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# The handler for a UART break detected by the PIO.
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def handler(sm):
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print("break", time.ticks_ms(), end=" ")
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# Function for core1 to execute to write to the given UART.
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def core1_task(uart, text):
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uart.write(text)
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# Set up the hard UART we're going to use to print characters.
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uart = UART(1, UART_BAUD, tx=HARD_UART_TX_PIN)
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for pio_prog in ("uart_rx_mini", "uart_rx"):
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# Set up the state machine we're going to use to receive the characters.
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sm = StateMachine(
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0,
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globals()[pio_prog],
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freq=8 * UART_BAUD,
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in_base=PIO_RX_PIN, # For WAIT, IN
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jmp_pin=PIO_RX_PIN, # For JMP
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)
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sm.irq(handler)
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sm.active(1)
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# Tell core 1 to print some text to UART 1
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text = "Hello, world from PIO, using {}!".format(pio_prog)
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_thread.start_new_thread(core1_task, (uart, text))
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# Echo characters received from PIO to the console.
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for i in range(len(text)):
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print(chr(sm.get() >> 24), end="")
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print()
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