import machine
import time
from rp2 import PIO, StateMachine, asm_pio

# --- Configuration ---
ZERO_CROSS_PIN = 16  # Input from zero-crossing detector
TRIAC_PIN = 17       # Output to TRIAC gate driver
AC_FREQUENCY = 60    # 60Hz or 50Hz

# --- Calculate Timing ---
HALF_CYCLE_US = int(1_000_000 / (2 * AC_FREQUENCY)) # 8333us for 60Hz

# --- PIO Assembly Program ---
@asm_pio(
    set_init=PIO.OUT_LOW, 
    in_shiftdir=PIO.SHIFT_LEFT, 
    autopull=True, 
    pull_thresh=32
)
def ac_phase_control():
    # 1. Wait for the Zero-Crossing edge to go HIGH
    wait(1, pin, 0)      
    
    # 2. Read the 32-bit delay count from the TX FIFO into the X register
    pull(noblock)        # Copies OSR to X if a new value is sent, else retains old value
    mov(x, osr)          
    
    # 3. Microsecond Delay Loop (X register acts as down-counter)
    label("delay_loop")
    jmp(x_dec, "delay_loop") [1] # Each loop takes 2 clock cycles (jmp + 1 delay cycle)
    
    # 4. Fire the TRIAC Gate Pulse
    set(pins, 1)         # Set TRIAC pin HIGH
    
    # 5. Hold the pulse duration (approx 100 microseconds)
    # At 1 MHz clock, 1 cycle = 1 us. We loop 50 times with a 1-cycle delay = 100 us.
    set(x, 49)           
    label("pulse_loop")
    jmp(x_dec, "pulse_loop") [1]
    
    set(pins, 0)         # Set TRIAC pin LOW (Pulse ends)
    
    # 6. Wait for the Zero-Crossing edge to go LOW before restarting
    wait(0, pin, 0)      

# --- Initialize PIO State Machine ---
# We configure the PIO clock frequency to exactly 1,000,000 Hz (1 MHz).
# This makes 1 clock cycle = 1 microsecond.
sm = StateMachine(
    0, 
    ac_phase_control, 
    freq=1_000_000, 
    set_base=machine.Pin(TRIAC_PIN), 
    in_base=machine.Pin(ZERO_CROSS_PIN)
)

# Active the state machine
sm.active(1)

# --- Helper Functions ---
def set_power_percentage(percent):
    """Sets power from 0% (off) to 100% (full on)."""
    percent = max(0, min(100, percent)) # Clamp between 0 and 100
    
    # Inverse relationship: 100% power = 0us delay, 0% power = Max delay
    delay_us = int(HALF_CYCLE_US * (100 - percent) / 100)
    
    # Prevent logic collisions at the very extremes
    delay_us = max(50, min(HALF_CYCLE_US - 200, delay_us))
    
    # The PIO loop takes 2 cycles per iteration. 
    # Therefore, the value sent must be divided by 2.
    pio_value = delay_us // 2
    
    # Push the countdown value to the PIO TX FIFO buffer
    sm.put(pio_value)
    print(f"Power: {percent}%, PIO Countdown: {pio_value}")

# --- Main Demo Loop ---
try:
    while True:
        # Fade up
        for p in range(0, 101, 2):
            set_power_percentage(p)
            time.sleep(0.05)
        # Fade down
        for p in range(100, -1, -2):
            set_power_percentage(p)
            time.sleep(0.05)
            
except KeyboardInterrupt:
    sm.active(0)
    # Force safe shutdown of the TRIAC pin
    machine.Pin(TRIAC_PIN, machine.Pin.OUT).low()
    print("PIO Program stopped safely.")