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| 1 | +# Example using PIO to create a UART RX interface. |
| 2 | +# |
| 3 | +# To make it work you'll need a wire connecting GPIO4 and GPIO3. |
| 4 | +# |
| 5 | +# Demonstrates: |
| 6 | +# - PIO shifting in data on a pin |
| 7 | +# - PIO jmp(pin) instruction |
| 8 | +# - PIO irq handler |
| 9 | +# - using the second core via _thread |
| 10 | + |
| 11 | +import _thread |
| 12 | +from machine import Pin, UART |
| 13 | +from rp2 import PIO, StateMachine, asm_pio |
| 14 | + |
| 15 | +UART_BAUD = 9600 |
| 16 | + |
| 17 | +HARD_UART_TX_PIN = Pin(4, Pin.OUT) |
| 18 | +PIO_RX_PIN = Pin(3, Pin.IN, Pin.PULL_UP) |
| 19 | + |
| 20 | + |
| 21 | +@asm_pio( |
| 22 | + autopush=True, |
| 23 | + push_thresh=8, |
| 24 | + in_shiftdir=rp2.PIO.SHIFT_RIGHT, |
| 25 | +) |
| 26 | +def uart_rx_mini(): |
| 27 | + # fmt: off |
| 28 | + # Wait for start bit |
| 29 | + wait(0, pin, 0) |
| 30 | + # Preload bit counter, delay until eye of first data bit |
| 31 | + set(x, 7) [10] |
| 32 | + # Loop 8 times |
| 33 | + label("bitloop") |
| 34 | + # Sample data |
| 35 | + in_(pins, 1) |
| 36 | + # Each iteration is 8 cycles |
| 37 | + jmp(x_dec, "bitloop") [6] |
| 38 | + # fmt: on |
| 39 | + |
| 40 | + |
| 41 | +@asm_pio( |
| 42 | + in_shiftdir=rp2.PIO.SHIFT_RIGHT, |
| 43 | +) |
| 44 | +def uart_rx(): |
| 45 | + # fmt: off |
| 46 | + label("start") |
| 47 | + # Stall until start bit is asserted |
| 48 | + wait(0, pin, 0) |
| 49 | + # Preload bit counter, then delay until halfway through |
| 50 | + # the first data bit (12 cycles incl wait, set). |
| 51 | + set(x, 7) [10] |
| 52 | + label("bitloop") |
| 53 | + # Shift data bit into ISR |
| 54 | + in_(pins, 1) |
| 55 | + # Loop 8 times, each loop iteration is 8 cycles |
| 56 | + jmp(x_dec, "bitloop") [6] |
| 57 | + # Check stop bit (should be high) |
| 58 | + jmp(pin, "good_stop") |
| 59 | + # Either a framing error or a break. Set a sticky flag |
| 60 | + # and wait for line to return to idle state. |
| 61 | + irq(block, 4) |
| 62 | + wait(1, pin, 0) |
| 63 | + # Don't push data if we didn't see good framing. |
| 64 | + jmp("start") |
| 65 | + # No delay before returning to start; a little slack is |
| 66 | + # important in case the TX clock is slightly too fast. |
| 67 | + label("good_stop") |
| 68 | + push(block) |
| 69 | + # fmt: on |
| 70 | + |
| 71 | + |
| 72 | +# The handler for a UART break detected by the PIO. |
| 73 | +def handler(sm): |
| 74 | + print("break", time.ticks_ms(), end=" ") |
| 75 | + |
| 76 | + |
| 77 | +# Function for core1 to execute to write to the given UART. |
| 78 | +def core1_task(uart, text): |
| 79 | + uart.write(text) |
| 80 | + |
| 81 | + |
| 82 | +# Set up the hard UART we're going to use to print characters. |
| 83 | +uart = UART(1, UART_BAUD, tx=HARD_UART_TX_PIN) |
| 84 | + |
| 85 | +for pio_prog in ("uart_rx_mini", "uart_rx"): |
| 86 | + # Set up the state machine we're going to use to receive the characters. |
| 87 | + sm = StateMachine( |
| 88 | + 0, |
| 89 | + globals()[pio_prog], |
| 90 | + freq=8 * UART_BAUD, |
| 91 | + in_base=PIO_RX_PIN, # For WAIT, IN |
| 92 | + jmp_pin=PIO_RX_PIN, # For JMP |
| 93 | + ) |
| 94 | + sm.irq(handler) |
| 95 | + sm.active(1) |
| 96 | + |
| 97 | + # Tell core 1 to print some text to UART 1 |
| 98 | + text = "Hello, world from PIO, using {}!".format(pio_prog) |
| 99 | + _thread.start_new_thread(core1_task, (uart, text)) |
| 100 | + |
| 101 | + # Echo characters received from PIO to the console. |
| 102 | + for i in range(len(text)): |
| 103 | + print(chr(sm.get() >> 24), end="") |
| 104 | + print() |
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