# Example using PIO to create a UART TX interface

def start()
    from machine import Pin
    from rp2 import PIO, StateMachine, asm_pio

    UART_BAUD = 115200
    PIN_BASE = 10
    NUM_UARTS = 8


    @asm_pio(sideset_init=PIO.OUT_HIGH, out_init=PIO.OUT_HIGH, out_shiftdir=PIO.SHIFT_RIGHT)
    def uart_tx():
        # Block with TX deasserted until data available
        pull()
        # Initialise bit counter, assert start bit for 8 cycles
        set(x, 7)  .side(0)       [7]
        # Shift out 8 data bits, 8 execution cycles per bit
        label("bitloop")
        out(pins, 1)              [6]
        jmp(x_dec, "bitloop")
        # Assert stop bit for 8 cycles total (incl 1 for pull())
        nop()      .side(1)       [6]


    # Now we add 8 UART TXs, on pins 10 to 17. Use the same baud rate for all of them.
    uarts = []
    for i in range(NUM_UARTS):
        sm = StateMachine(
            i, uart_tx, freq=8 * UART_BAUD, sideset_base=Pin(PIN_BASE + i), out_base=Pin(PIN_BASE + i)
        )
        sm.active(1)
        uarts.append(sm)

    # We can print characters from each UART by pushing them to the TX FIFO
    def pio_uart_print(sm, s):
        for c in s:
            sm.put(ord(c))


    # Print a different message from each UART
    for i, u in enumerate(uarts):
        pio_uart_print(u, "Hello from UART {}!\n".format(i))