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45 lines
1.2 KiB
45 lines
1.2 KiB
4 years ago
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# Example using PIO to create a UART TX interface
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from machine import Pin
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from rp2 import PIO, StateMachine, asm_pio
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UART_BAUD = 115200
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PIN_BASE = 10
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NUM_UARTS = 8
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@asm_pio(sideset_init=PIO.OUT_HIGH, out_init=PIO.OUT_HIGH, out_shiftdir=PIO.SHIFT_RIGHT)
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def uart_tx():
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# fmt: off
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# Block with TX deasserted until data available
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pull()
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# Initialise bit counter, assert start bit for 8 cycles
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set(x, 7) .side(0) [7]
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# Shift out 8 data bits, 8 execution cycles per bit
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label("bitloop")
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out(pins, 1) [6]
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jmp(x_dec, "bitloop")
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# Assert stop bit for 8 cycles total (incl 1 for pull())
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nop() .side(1) [6]
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# fmt: on
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# Now we add 8 UART TXs, on pins 10 to 17. Use the same baud rate for all of them.
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uarts = []
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for i in range(NUM_UARTS):
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sm = StateMachine(
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i, uart_tx, freq=8 * UART_BAUD, sideset_base=Pin(PIN_BASE + i), out_base=Pin(PIN_BASE + i)
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)
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sm.active(1)
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uarts.append(sm)
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# We can print characters from each UART by pushing them to the TX FIFO
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def pio_uart_print(sm, s):
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for c in s:
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sm.put(ord(c))
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# Print a different message from each UART
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for i, u in enumerate(uarts):
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pio_uart_print(u, "Hello from UART {}!\n".format(i))
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