//! This example shows generating audio and sending it to a connected i2s DAC using the PIO
//! module of the RP2040.
//!
//! Connect the i2s DAC as follows:
//!   bclk : GPIO 18
//!   lrc  : GPIO 19
//!   din  : GPIO 20
//! Then hold down the boot select button to trigger a rising triangle waveform.

#![no_std]
#![no_main]

use core::mem;

use embassy_executor::Spawner;
use embassy_rp::peripherals::PIO0;
use embassy_rp::pio::{Config, FifoJoin, InterruptHandler, Pio, ShiftConfig, ShiftDirection};
use embassy_rp::{bind_interrupts, Peripheral};
use fixed::traits::ToFixed;
use static_cell::StaticCell;
use {defmt_rtt as _, panic_probe as _};

bind_interrupts!(struct Irqs {
    PIO0_IRQ_0 => InterruptHandler<PIO0>;
});

const SAMPLE_RATE: u32 = 48_000;

#[embassy_executor::main]
async fn main(_spawner: Spawner) {
    let mut p = embassy_rp::init(Default::default());

    // Setup pio state machine for i2s output
    let mut pio = Pio::new(p.PIO0, Irqs);

    #[rustfmt::skip]
    let pio_program = pio_proc::pio_asm!(
        ".side_set 2",
        "    set x, 14          side 0b01", // side 0bWB - W = Word Clock, B = Bit Clock
        "left_data:",
        "    out pins, 1        side 0b00",
        "    jmp x-- left_data  side 0b01",
        "    out pins 1         side 0b10",
        "    set x, 14          side 0b11",
        "right_data:",
        "    out pins 1         side 0b10",
        "    jmp x-- right_data side 0b11",
        "    out pins 1         side 0b00",
    );

    let bit_clock_pin = p.PIN_18;
    let left_right_clock_pin = p.PIN_19;
    let data_pin = p.PIN_20;

    let data_pin = pio.common.make_pio_pin(data_pin);
    let bit_clock_pin = pio.common.make_pio_pin(bit_clock_pin);
    let left_right_clock_pin = pio.common.make_pio_pin(left_right_clock_pin);

    let cfg = {
        let mut cfg = Config::default();
        cfg.use_program(
            &pio.common.load_program(&pio_program.program),
            &[&bit_clock_pin, &left_right_clock_pin],
        );
        cfg.set_out_pins(&[&data_pin]);
        const BIT_DEPTH: u32 = 16;
        const CHANNELS: u32 = 2;
        let clock_frequency = SAMPLE_RATE * BIT_DEPTH * CHANNELS;
        cfg.clock_divider = (125_000_000. / clock_frequency as f64 / 2.).to_fixed();
        cfg.shift_out = ShiftConfig {
            threshold: 32,
            direction: ShiftDirection::Left,
            auto_fill: true,
        };
        // join fifos to have twice the time to start the next dma transfer
        cfg.fifo_join = FifoJoin::TxOnly;
        cfg
    };
    pio.sm0.set_config(&cfg);
    pio.sm0.set_pin_dirs(
        embassy_rp::pio::Direction::Out,
        &[&data_pin, &left_right_clock_pin, &bit_clock_pin],
    );

    // create two audio buffers (back and front) which will take turns being
    // filled with new audio data and being sent to the pio fifo using dma
    const BUFFER_SIZE: usize = 960;
    static DMA_BUFFER: StaticCell<[u32; BUFFER_SIZE * 2]> = StaticCell::new();
    let dma_buffer = DMA_BUFFER.init_with(|| [0u32; BUFFER_SIZE * 2]);
    let (mut back_buffer, mut front_buffer) = dma_buffer.split_at_mut(BUFFER_SIZE);

    // start pio state machine
    pio.sm0.set_enable(true);
    let tx = pio.sm0.tx();
    let mut dma_ref = p.DMA_CH0.into_ref();

    let mut fade_value: i32 = 0;
    let mut phase: i32 = 0;

    loop {
        // trigger transfer of front buffer data to the pio fifo
        // but don't await the returned future, yet
        let dma_future = tx.dma_push(dma_ref.reborrow(), front_buffer);

        // fade in audio when bootsel is pressed
        let fade_target = if p.BOOTSEL.is_pressed() { i32::MAX } else { 0 };

        // fill back buffer with fresh audio samples before awaiting the dma future
        for s in back_buffer.iter_mut() {
            // exponential approach of fade_value => fade_target
            fade_value += (fade_target - fade_value) >> 14;
            // generate triangle wave with amplitude and frequency based on fade value
            phase = (phase + (fade_value >> 22)) & 0xffff;
            let triangle_sample = (phase as i16 as i32).abs() - 16384;
            let sample = (triangle_sample * (fade_value >> 15)) >> 16;
            // duplicate mono sample into lower and upper half of dma word
            *s = (sample as u16 as u32) * 0x10001;
        }

        // now await the dma future. once the dma finishes, the next buffer needs to be queued
        // within DMA_DEPTH / SAMPLE_RATE = 8 / 48000 seconds = 166us
        dma_future.await;
        mem::swap(&mut back_buffer, &mut front_buffer);
    }
}