import sys
import time
from machine import Pin

# Define pins for software inverted UART
# GP2: TX, GP3: RX
tx_pin = Pin(2, Pin.OUT, value=0)  # Idle state is Low (0)
rx_pin = Pin(3, Pin.IN, Pin.PULL_DOWN)  # Idle state is Low

BAUD_RATE = 9600
BIT_TIME_US = int(1000000 / BAUD_RATE)  # Duration of one bit in microseconds (~104us)


def send_byte(b):
  # Start bit: High (1) for inverted UART
  tx_pin.value(1)
  time.sleep_us(BIT_TIME_US)

  # 8 Data bits (LSB first)
  for i in range(8):
    bit = (b >> i) & 1
    tx_pin.value(bit)
    time.sleep_us(BIT_TIME_US)

  # 2 Stop bits: Low (0) - returning to idle level
  tx_pin.value(0)
  time.sleep_us(BIT_TIME_US * 2)


def receive_byte():
  # Wait for start bit (transition from Low to High)
  timeout_count = 0
  while rx_pin.value() == 0:
    timeout_count += 1
    if timeout_count > 200000:  # Timeout guard
      return None

  # Center sample: Wait 1 full bit time (start bit) + half bit time
  time.sleep_us(BIT_TIME_US + BIT_TIME_US // 2)

  data = 0
  for i in range(8):
    bit = rx_pin.value()
    data |= bit << i
    time.sleep_us(BIT_TIME_US)

  # Wait through the stop bits
  time.sleep_us(BIT_TIME_US * 2)
  return data


print("Software Inverted UART Ready. Type a string and press Enter:")

while True:
  line = sys.stdin.readline()
  if not line:
    continue
  text = line.strip()
  if not text:
    continue

  print(f"Transmitting: {text}")
  received_chars = []

  for char in text:
    b = ord(char)
    send_byte(b)
    # Receive back via loopback connection
    rx_b = receive_byte()
    if rx_b is not None:
      received_chars.append(chr(rx_b))
    else:
      received_chars.append("?")

  decoded_str = "".join(received_chars)
  print(f"Received (Decoded): {decoded_str}")