uart_bridge.py
#!/usr/bin/env python3
#
# This file is part of LUNA.
#
"""
Example of using the debug controller's UART bridge.

Connect to the ttyACM connection at 115200 baud, 8N1,
and you should see "Hello World" 'typed' repeatedly.
"""

from nmigen import Signal, Elaboratable, Module, Array, Cat

from luna import top_level_cli
from luna.gateware.interface.uart import UARTTransmitter


class UARTBridgeExample(Elaboratable):

    def elaborate(self, platform):
        m = Module()
        uart = platform.request("uart")

        clock_freq = int(60e6)
        char_freq  = int(6e6)

        # Create our UART transmitter.
        transmitter = UARTTransmitter(divisor=int(clock_freq // 115200))
        m.submodules.transmitter = transmitter

        # Create a counter that will let us transmit ten times per second.
        counter = Signal(range(0, char_freq))
        with m.If(counter == (char_freq - 1)):
            m.d.sync += counter.eq(0)
        with m.Else():
            m.d.sync += counter.eq(counter + 1)

        # Create a simple ROM with a message for ourselves...
        letters = Array(ord(i) for i in "Hello, world! \r\n")

        # ... and count through it whenever we send a letter.
        current_letter = Signal(range(0, len(letters)))
        with m.If(transmitter.accepted):
            m.d.sync += current_letter.eq(current_letter + 1)


        # Hook everything up.
        m.d.comb += [
            transmitter.data.eq(letters[current_letter]),
            transmitter.send.eq(counter == 0),

            uart.tx.eq(transmitter.tx)
        ]


        # Turn on a single LED, just to show something's running.
        led = Cat(platform.request('led', i) for i in range(6))
        m.d.comb += led.eq(~transmitter.tx)

        return m


if __name__ == "__main__":
    top_level_cli(UARTBridgeExample)