Merge branch 'audio-driver'

Cargo.lock

@@ -898,6 +898,14 @@ dependencies = [
  "rlsf",
 ]
 
+[[package]]
+name = "embedded-audio"
+version = "0.1.0"
+source = "git+https://github.com/LegitCamper/embedded-audio#087784644d810b94dd659a03dbed4795dfb0bd24"
+dependencies = [
+ "heapless",
+]
+
 [[package]]
 name = "embedded-graphics"
 version = "0.8.1"
@@ -1470,8 +1478,10 @@ dependencies = [
  "embedded-layout",
  "embedded-sdmmc",
  "embedded-text",
+ "fixed",
  "goblin",
  "heapless",
+ "micromath",
  "num_enum 0.7.5",
  "once_cell",
  "panic-probe",
@@ -2744,6 +2754,17 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "wav_player"
+version = "0.1.0"
+dependencies = [
+ "abi",
+ "embedded-audio",
+ "embedded-graphics",
+ "rand",
+ "selection_ui",
+]
+
 [[package]]
 name = "winapi"
 version = "0.3.9"

Cargo.toml

@@ -9,6 +9,7 @@ members = [
   "user-apps/snake",
   "user-apps/gallery",
   "user-apps/gif",
+  "user-apps/wav_player",
 ]
 
 [profile.release]

abi/src/lib.rs

@@ -3,7 +3,7 @@
 
 extern crate alloc;
 
-use abi_sys::{RngRequest, alloc, dealloc, keyboard::KeyEvent};
+use abi_sys::{RngRequest, keyboard::KeyEvent};
 pub use abi_sys::{keyboard, print};
 pub use alloc::format;
 use core::alloc::{GlobalAlloc, Layout};
@@ -16,11 +16,11 @@ struct Alloc;
 
 unsafe impl GlobalAlloc for Alloc {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        alloc(layout.into())
+        abi_sys::alloc(layout.into())
     }
 
     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
-        dealloc(ptr, layout.into());
+        abi_sys::dealloc(ptr, layout.into());
     }
 }
 
@@ -267,3 +267,11 @@ pub mod fs {
         abi_sys::file_len(str.as_ptr(), str.len())
     }
 }
+
+pub mod audio {
+    pub use abi_sys::{AUDIO_BUFFER_LEN, AUDIO_BUFFER_SAMPLES, audio_buffer_ready};
+
+    pub fn send_audio_buffer(buf: &[u8]) {
+        abi_sys::send_audio_buffer(buf.as_ptr(), buf.len())
+    }
+}

abi_sys/src/lib.rs

@@ -12,7 +12,7 @@ use strum::{EnumCount, EnumIter};
 
 pub type EntryFn = fn();
 
-pub const ABI_CALL_TABLE_COUNT: usize = 12;
+pub const ABI_CALL_TABLE_COUNT: usize = 14;
 const _: () = assert!(ABI_CALL_TABLE_COUNT == CallTable::COUNT);
 
 #[derive(Clone, Copy, EnumIter, EnumCount)]
@@ -30,6 +30,8 @@ pub enum CallTable {
     ReadFile = 9,
     WriteFile = 10,
     FileLen = 11,
+    AudioBufferReady = 12,
+    SendAudioBuffer = 13,
 }
 
 #[unsafe(no_mangle)]
@@ -467,3 +469,28 @@ pub extern "C" fn file_len(str: *const u8, len: usize) -> usize {
         f(str, len)
     }
 }
+
+pub type AudioBufferReady = extern "C" fn() -> bool;
+
+#[allow(unused)]
+pub fn audio_buffer_ready() -> bool {
+    unsafe {
+        let ptr = CALL_ABI_TABLE[CallTable::AudioBufferReady as usize];
+        let f: AudioBufferReady = core::mem::transmute(ptr);
+        f()
+    }
+}
+
+pub const AUDIO_BUFFER_SAMPLES: usize = 1024;
+pub const AUDIO_BUFFER_LEN: usize = AUDIO_BUFFER_SAMPLES * 2;
+
+pub type SendAudioBuffer = extern "C" fn(ptr: *const u8, len: usize);
+
+#[allow(unused)]
+pub fn send_audio_buffer(buf: *const u8, len: usize) {
+    unsafe {
+        let ptr = CALL_ABI_TABLE[CallTable::SendAudioBuffer as usize];
+        let f: SendAudioBuffer = core::mem::transmute(ptr);
+        f(buf, len)
+    }
+}

justfile

@@ -39,6 +39,7 @@ userapps: cbindgen
     just userapp snake
     just userapp gallery
     just userapp gif
+    just userapp wav_player
 
 copy-userapp app:
     cp ./target/thumbv8m.main-none-eabihf/release-binary/{{app}} /run/media/$(whoami)/PICOCALC/{{app}}.bin
@@ -50,6 +51,7 @@ copy-userapps:
     just copy-userapp snake
     just copy-userapp gallery
     just copy-userapp gif
+    just copy-userapp wav_player
 
     DEV=$(lsblk -o LABEL,NAME -nr | awk -v L="PICOCALC" '$1==L {print "/dev/" $2}')
     udisksctl unmount -b "$DEV"

kernel/Cargo.toml

@@ -82,6 +82,8 @@ embedded-graphics = { version = "0.8.1" }
 embedded-text = "0.7.2"
 embedded-layout = "0.4.2"
 
+micromath = "2.1.0"
+fixed = "1.29.0"
 strum = { version = "0.27.2", default-features = false }
 rand = { version = "0.9.0", default-features = false }
 once_cell = { version = "1.21.3", default-features = false }

kernel/src/abi.rs

@@ -1,6 +1,7 @@
 use abi_sys::{
-    AllocAbi, CLayout, CPixel, DeallocAbi, DrawIterAbi, FileLen, GenRand, GetMsAbi, ListDir,
+    AUDIO_BUFFER_SAMPLES, AllocAbi, AudioBufferReady, CLayout, CPixel, DeallocAbi, DrawIterAbi,
-    PrintAbi, ReadFile, RngRequest, SleepMsAbi, WriteFile, keyboard::*,
+    FileLen, GenRand, GetMsAbi, ListDir, PrintAbi, ReadFile, RngRequest, SendAudioBuffer,
+    SleepMsAbi, WriteFile, keyboard::*,
 };
 use alloc::{string::ToString, vec::Vec};
 use core::{ffi::c_char, ptr, sync::atomic::Ordering};
@@ -17,6 +18,7 @@ use crate::heap::HEAP;
 use core::alloc::GlobalAlloc;
 
 use crate::{
+    audio::{AUDIO_BUFFER, AUDIO_BUFFER_READY},
     display::FRAMEBUFFER,
     framebuffer::FB_PAUSED,
     storage::{Dir, File, SDCARD},
@@ -207,7 +209,6 @@ fn recurse_file<T>(
     dirs: &[&str],
     mut access: impl FnMut(&mut File) -> T,
 ) -> Result<T, ()> {
-    defmt::info!("dir: {}, dirs: {}", dir, dirs);
     if dirs.len() == 1 {
         let mut b = [0_u8; 50];
         let mut buf = LfnBuffer::new(&mut b);
@@ -331,3 +332,28 @@ pub extern "C" fn file_len(str: *const u8, len: usize) -> usize {
     }
     len as usize
 }
+
+const _: AudioBufferReady = audio_buffer_ready;
+pub extern "C" fn audio_buffer_ready() -> bool {
+    AUDIO_BUFFER_READY.load(Ordering::Acquire)
+}
+
+const _: SendAudioBuffer = send_audio_buffer;
+pub extern "C" fn send_audio_buffer(ptr: *const u8, len: usize) {
+    // SAFETY: caller guarantees `ptr` is valid for `len` bytes
+    let buf = unsafe { core::slice::from_raw_parts(ptr, len) };
+
+    while !AUDIO_BUFFER_READY.load(Ordering::Acquire) {}
+
+    if buf.len() == AUDIO_BUFFER_SAMPLES * 2 {
+        AUDIO_BUFFER_READY.store(false, Ordering::Release);
+        unsafe { AUDIO_BUFFER.copy_from_slice(buf) };
+    } else {
+        #[cfg(feature = "defmt")]
+        defmt::warn!(
+            "user audio stream was wrong size: {} should be {}",
+            buf.len(),
+            AUDIO_BUFFER_SAMPLES * 2
+        )
+    }
+}

kernel/src/audio.rs

@@ -0,0 +1,149 @@
+use crate::Audio;
+use core::sync::atomic::{AtomicBool, Ordering};
+use embassy_futures::join::join;
+use embassy_rp::{
+    Peri,
+    clocks::clk_sys_freq,
+    dma::{AnyChannel, Channel},
+    gpio::Level,
+    pio::{
+        Common, Config, Direction, FifoJoin, Instance, LoadedProgram, PioPin, ShiftConfig,
+        StateMachine, program::pio_asm,
+    },
+};
+use fixed::traits::ToFixed;
+
+pub const SAMPLE_RATE_HZ: u32 = 22_050;
+const AUDIO_BUFFER_SAMPLES: usize = 1024;
+const _: () = assert!(AUDIO_BUFFER_SAMPLES == abi_sys::AUDIO_BUFFER_SAMPLES);
+
+// 8bit stereo interleaved PCM audio buffers
+pub static mut AUDIO_BUFFER: [u8; AUDIO_BUFFER_SAMPLES * 2] = [0; AUDIO_BUFFER_SAMPLES * 2];
+static mut AUDIO_BUFFER_1: [u8; AUDIO_BUFFER_SAMPLES * 2] = [0; AUDIO_BUFFER_SAMPLES * 2];
+
+pub static AUDIO_BUFFER_READY: AtomicBool = AtomicBool::new(true);
+
+#[embassy_executor::task]
+pub async fn audio_handler(mut audio: Audio) {
+    const SILENCE_VALUE: u8 = u8::MAX / 2;
+
+    let prg = PioPwmAudioProgram8Bit::new(&mut audio.pio);
+    let mut pwm_pio_left =
+        PioPwmAudio::new(audio.dma0, &mut audio.pio, audio.sm0, audio.left, &prg);
+    let mut pwm_pio_right =
+        PioPwmAudio::new(audio.dma1, &mut audio.pio, audio.sm1, audio.right, &prg);
+
+    loop {
+        write_samples(&mut pwm_pio_left, &mut pwm_pio_right, unsafe {
+            &AUDIO_BUFFER_1
+        })
+        .await;
+        unsafe { &mut AUDIO_BUFFER_1 }.fill(SILENCE_VALUE);
+
+        unsafe { core::mem::swap(&mut AUDIO_BUFFER, &mut AUDIO_BUFFER_1) };
+        AUDIO_BUFFER_READY.store(true, Ordering::Release)
+    }
+}
+
+async fn write_samples<PIO: Instance>(
+    left: &mut PioPwmAudio<'static, PIO, 0>,
+    right: &mut PioPwmAudio<'static, PIO, 1>,
+    buf: &[u8],
+) {
+    // pack two samples per word
+    let mut packed_buf_left: [u32; AUDIO_BUFFER_SAMPLES / 2] = [0; AUDIO_BUFFER_SAMPLES / 2];
+    let mut packed_buf_right: [u32; AUDIO_BUFFER_SAMPLES / 2] = [0; AUDIO_BUFFER_SAMPLES / 2];
+
+    for ((pl, pr), sample) in packed_buf_left
+        .iter_mut()
+        .zip(packed_buf_right.iter_mut())
+        .zip(buf.chunks(4))
+    {
+        *pl = pack_u8_samples(sample[0], sample[2]);
+        *pr = pack_u8_samples(sample[1], sample[3]);
+    }
+
+    let left_fut = left
+        .sm
+        .tx()
+        .dma_push(left.dma.reborrow(), &packed_buf_left, false);
+
+    let right_fut = right
+        .sm
+        .tx()
+        .dma_push(right.dma.reborrow(), &packed_buf_right, false);
+
+    join(left_fut, right_fut).await;
+}
+
+struct PioPwmAudioProgram8Bit<'d, PIO: Instance>(LoadedProgram<'d, PIO>);
+
+/// Writes one sample to pwm as high and low time
+impl<'d, PIO: Instance> PioPwmAudioProgram8Bit<'d, PIO> {
+    fn new(common: &mut Common<'d, PIO>) -> Self {
+        // only uses 16 bits top for high, bottom for low
+        // allows two samples per word
+        let prg = pio_asm!(
+            "out x, 8", // pwm high time
+            "out y, 8", // pwm low time
+            "loop_high:",
+            "set pins, 1",       // keep pin high
+            "jmp x-- loop_high", // decrement X until 0
+            "loop_low:",
+            "set pins, 0",      // keep pin low
+            "jmp y-- loop_low", // decrement Y until 0
+        );
+
+        let prg = common.load_program(&prg.program);
+
+        Self(prg)
+    }
+}
+
+struct PioPwmAudio<'d, PIO: Instance, const SM: usize> {
+    dma: Peri<'d, AnyChannel>,
+    sm: StateMachine<'d, PIO, SM>,
+}
+
+impl<'d, PIO: Instance, const SM: usize> PioPwmAudio<'d, PIO, SM> {
+    fn new(
+        dma: Peri<'d, impl Channel>,
+        pio: &mut Common<'d, PIO>,
+        mut sm: StateMachine<'d, PIO, SM>,
+        pin: Peri<'d, impl PioPin>,
+        prg: &PioPwmAudioProgram8Bit<'d, PIO>,
+    ) -> Self {
+        let pin = pio.make_pio_pin(pin);
+        sm.set_pins(Level::High, &[&pin]);
+        sm.set_pin_dirs(Direction::Out, &[&pin]);
+
+        let mut cfg = Config::default();
+        cfg.set_set_pins(&[&pin]);
+        cfg.fifo_join = FifoJoin::TxOnly;
+        let mut shift_cfg = ShiftConfig::default();
+        shift_cfg.auto_fill = true;
+        cfg.shift_out = shift_cfg;
+        cfg.use_program(&prg.0, &[]);
+        sm.set_config(&cfg);
+
+        let target_clock = (u8::MAX as u32 + 1) * SAMPLE_RATE_HZ;
+        let divider = (clk_sys_freq() / (target_clock * 2)).to_fixed();
+        sm.set_clock_divider(divider);
+
+        sm.set_enable(true);
+
+        Self {
+            dma: dma.into(),
+            sm,
+        }
+    }
+}
+
+/// packs two u8 samples into 32bit word
+fn pack_u8_samples(sample1: u8, sample2: u8) -> u32 {
+    (u8_pcm_to_pwm(sample1) as u32) << 16 | u8_pcm_to_pwm(sample2) as u32
+}
+
+fn u8_pcm_to_pwm(sample: u8) -> u16 {
+    ((sample as u16) << 8) | ((u8::MAX - sample) as u16)
+}

kernel/src/display.rs

@@ -1,17 +1,15 @@
 use crate::framebuffer::{self, AtomicFrameBuffer, FB_PAUSED};
 use core::alloc::{GlobalAlloc, Layout};
 use core::sync::atomic::Ordering;
+use embassy_futures::yield_now;
 use embassy_rp::{
     Peri,
     gpio::{Level, Output},
     peripherals::{PIN_13, PIN_14, PIN_15, SPI1},
     spi::{Async, Spi},
 };
-use embassy_time::{Delay, Timer};
+use embassy_time::Delay;
-use embedded_graphics::{
+use embedded_graphics::{draw_target::DrawTarget, pixelcolor::Rgb565, prelude::RgbColor};
-    pixelcolor::Rgb565,
-    prelude::{DrawTarget, RgbColor},
-};
 use embedded_hal_bus::spi::ExclusiveDevice;
 use st7365p_lcd::ST7365P;
 
@@ -117,7 +115,7 @@ pub async fn display_handler(mut display: DISPLAY) {
         if elapsed < FRAME_TIME_MS {
             Timer::after_millis(FRAME_TIME_MS - elapsed).await;
         } else {
-            Timer::after_millis(1).await;
+            yield_now().await;
         }
     }
 }

kernel/src/elf.rs

@@ -2,8 +2,7 @@ use crate::{
     abi,
     storage::{File, SDCARD},
 };
-use abi_sys::CallTable;
+use abi_sys::{CallTable, EntryFn};
-use abi_sys::EntryFn;
 use alloc::{vec, vec::Vec};
 use bumpalo::Bump;
 use core::ptr;
@@ -208,6 +207,8 @@ fn patch_abi(
                             CallTable::ReadFile => abi::read_file as usize,
                             CallTable::WriteFile => abi::write_file as usize,
                             CallTable::FileLen => abi::file_len as usize,
+                            CallTable::AudioBufferReady => abi::audio_buffer_ready as usize,
+                            CallTable::SendAudioBuffer => abi::send_audio_buffer as usize,
                         };
                         unsafe {
                             table_base.add(idx as usize).write(ptr);

kernel/src/main.rs

@@ -9,6 +9,7 @@
 extern crate alloc;
 
 mod abi;
+mod audio;
 mod display;
 mod elf;
 mod framebuffer;
@@ -31,6 +32,7 @@ use crate::{heap::HEAP, heap::init_qmi_psram_heap, psram::init_psram, psram::ini
 
 use crate::{
     abi::{KEY_CACHE, MS_SINCE_LAUNCH},
+    audio::audio_handler,
     display::{FRAMEBUFFER, display_handler, init_display},
     peripherals::{
         conf_peripherals,
@@ -55,9 +57,9 @@ use embassy_rp::{
     peripherals::{
         DMA_CH0, DMA_CH1, DMA_CH3, DMA_CH4, I2C1, PIN_2, PIN_3, PIN_6, PIN_7, PIN_10, PIN_11,
         PIN_12, PIN_13, PIN_14, PIN_15, PIN_16, PIN_17, PIN_18, PIN_19, PIN_20, PIN_21, PIN_22,
-        PIO0, SPI0, SPI1, USB, WATCHDOG,
+        PIN_26, PIN_27, PIO0, SPI0, SPI1, USB, WATCHDOG,
     },
-    pio,
+    pio::{self, Common, Pio, StateMachine},
     spi::{self, Spi},
     usb as embassy_rp_usb,
     watchdog::{ResetReason, Watchdog},
@@ -119,10 +121,12 @@ async fn watchdog_task(mut watchdog: Watchdog) {
 static ENABLE_UI: AtomicBool = AtomicBool::new(true);
 static UI_CHANGE: Signal<CriticalSectionRawMutex, ()> = Signal::new();
 
+const OVERCLOCK: u32 = 300_000_000;
+
 #[embassy_executor::main]
 async fn main(_spawner: Spawner) {
     let p = if cfg!(feature = "overclock") {
-        let clocks = ClockConfig::system_freq(300_000_000).unwrap();
+        let clocks = ClockConfig::system_freq(OVERCLOCK).unwrap();
         let config = Config::new(clocks);
         embassy_rp::init(config)
     } else {
@@ -149,6 +153,19 @@ async fn main(_spawner: Spawner) {
         data: p.PIN_14,
         reset: p.PIN_15,
     };
+    let Pio {
+        common, sm0, sm1, ..
+    } = Pio::new(p.PIO0, Irqs);
+
+    let audio = Audio {
+        pio: common,
+        sm0,
+        dma0: p.DMA_CH3,
+        left: p.PIN_26,
+        sm1,
+        dma1: p.DMA_CH4,
+        right: p.PIN_27,
+    };
     let sd = Sd {
         spi: p.SPI0,
         clk: p.PIN_18,
@@ -157,15 +174,15 @@ async fn main(_spawner: Spawner) {
         cs: p.PIN_17,
         det: p.PIN_22,
     };
-    let psram = Psram {
+    // let psram = Psram {
-        pio: p.PIO0,
+    //     pio: p.PIO0,
-        sclk: p.PIN_21,
+    //     sclk: p.PIN_21,
-        mosi: p.PIN_2,
+    //     mosi: p.PIN_2,
-        miso: p.PIN_3,
+    //     miso: p.PIN_3,
-        cs: p.PIN_20,
+    //     cs: p.PIN_20,
-        dma1: p.DMA_CH3,
+    //     dma1: p.DMA_CH3,
-        dma2: p.DMA_CH4,
+    //     dma2: p.DMA_CH4,
-    };
+    // };
     let mcu = Mcu {
         i2c: p.I2C1,
         clk: p.PIN_7,
@@ -175,7 +192,7 @@ async fn main(_spawner: Spawner) {
     executor0.run(|spawner| {
         spawner
             .spawn(kernel_task(
-                spawner, p.WATCHDOG, display, sd, psram, mcu, p.USB,
+                spawner, p.WATCHDOG, display, audio, sd, mcu, p.USB,
             ))
             .unwrap()
     });
@@ -229,6 +246,15 @@ struct Display {
     data: Peri<'static, PIN_14>,
     reset: Peri<'static, PIN_15>,
 }
+struct Audio {
+    pio: Common<'static, PIO0>,
+    dma0: Peri<'static, DMA_CH3>,
+    sm0: StateMachine<'static, PIO0, 0>,
+    left: Peri<'static, PIN_26>,
+    dma1: Peri<'static, DMA_CH4>,
+    sm1: StateMachine<'static, PIO0, 1>,
+    right: Peri<'static, PIN_27>,
+}
 struct Sd {
     spi: Peri<'static, SPI0>,
     clk: Peri<'static, PIN_18>,
@@ -330,8 +356,9 @@ async fn kernel_task(
     spawner: Spawner,
     watchdog: Peri<'static, WATCHDOG>,
     display: Display,
+    audio: Audio,
     sd: Sd,
-    _psram: Psram,
+    // _psram: Psram,
     mcu: Mcu,
     usb: Peri<'static, USB>,
 ) {
@@ -356,6 +383,8 @@ async fn kernel_task(
     setup_display(display, spawner).await;
     setup_sd(sd).await;
 
+    spawner.spawn(audio_handler(audio)).unwrap();
+
     let _usb = embassy_rp_usb::Driver::new(usb, Irqs);
     // spawner.spawn(usb_handler(usb)).unwrap();
 

user-apps/wav_player/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "wav_player"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+abi = { path = "../../abi" }
+selection_ui = { path = "../../selection_ui" }
+embedded-graphics = "0.8.1"
+rand = { version = "0.9.0", default-features = false }
+embedded-audio = { git = "https://github.com/LegitCamper/embedded-audio" }

user-apps/wav_player/build.rs

@@ -0,0 +1,28 @@
+//! This build script copies the `memory.x` file from the crate root into
+//! a directory where the linker can always find it at build time.
+//! For many projects this is optional, as the linker always searches the
+//! project root directory -- wherever `Cargo.toml` is. However, if you
+//! are using a workspace or have a more complicated build setup, this
+//! build script becomes required. Additionally, by requesting that
+//! Cargo re-run the build script whenever `memory.x` is changed,
+//! updating `memory.x` ensures a rebuild of the application with the
+//! new memory settings.
+
+use std::env;
+use std::fs::File;
+use std::io::Write;
+use std::path::PathBuf;
+
+fn main() {
+    // Put `memory.x` in our output directory and ensure it's
+    // on the linker search path.
+    let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
+    File::create(out.join("memory.x"))
+        .unwrap()
+        .write_all(include_bytes!("../memory.x"))
+        .unwrap();
+    println!("cargo:rustc-link-search={}", out.display());
+
+    println!("cargo:rerun-if-changed=memory.x");
+    println!("cargo:rustc-link-arg-bins=-Tmemory.x");
+}

user-apps/wav_player/src/main.rs

@@ -0,0 +1,139 @@
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+use abi::{
+    audio::{AUDIO_BUFFER_LEN, audio_buffer_ready, send_audio_buffer},
+    display::Display,
+    format,
+    fs::{Entries, file_len, list_dir, read_file},
+    get_key,
+    keyboard::{KeyCode, KeyState},
+    println,
+};
+use alloc::{string::String, vec::Vec};
+use core::panic::PanicInfo;
+use embedded_audio::{AudioFile, PlatformFile, PlatformFileError, wav::Wav};
+use embedded_graphics::{
+    mono_font::{MonoTextStyle, ascii::FONT_6X10},
+    pixelcolor::Rgb565,
+    prelude::RgbColor,
+};
+use selection_ui::{SelectionUi, SelectionUiError, draw_text_center};
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    println!("user panic: {} @ {:?}", info.message(), info.location(),);
+    loop {}
+}
+
+#[unsafe(no_mangle)]
+pub extern "Rust" fn _start() {
+    main()
+}
+
+pub fn main() {
+    println!("Starting Wav player app");
+    let mut display = Display::take().unwrap();
+
+    loop {
+        let mut entries = Entries::new();
+        list_dir("/music", &mut entries);
+
+        let mut files = entries.entries();
+        files.retain(|e| e.extension().unwrap_or("") == "wav");
+        let mut wavs = files.iter().map(|e| e.full_name()).collect::<Vec<&str>>();
+        wavs.sort();
+
+        let mut selection_ui = SelectionUi::new(&mut wavs);
+        let selection = match selection_ui.run_selection_ui(&mut display) {
+            Ok(maybe_sel) => maybe_sel,
+            Err(e) => match e {
+                SelectionUiError::SelectionListEmpty => {
+                    draw_text_center(
+                        &mut display,
+                        "No Wavs were found in /gifs",
+                        MonoTextStyle::new(&FONT_6X10, Rgb565::RED),
+                    )
+                    .expect("Display Error");
+                    None
+                }
+                SelectionUiError::DisplayError(_) => panic!("Display Error"),
+            },
+        };
+
+        assert!(selection.is_some());
+
+        let file_name = format!("/music/{}", wavs[selection.unwrap()]);
+        let file = File::new(String::from(file_name));
+        let mut wav = Wav::new(file).unwrap();
+        println!("sample rate: {}", wav.sample_rate());
+        println!("channels: {:?}", wav.channels() as u8);
+
+        let mut buf = [0_u8; AUDIO_BUFFER_LEN];
+
+        loop {
+            if audio_buffer_ready() {
+                if wav.is_eof() {
+                    break;
+                }
+
+                let _read = wav.read(&mut buf).unwrap();
+                send_audio_buffer(&buf);
+            }
+
+            let event = get_key();
+            if event.state == KeyState::Released {
+                match event.key {
+                    KeyCode::Esc => return,
+                    _ => (),
+                }
+            }
+        }
+    }
+}
+
+struct File {
+    current_pos: usize,
+    file: String,
+}
+
+impl File {
+    fn new(file: String) -> Self {
+        Self {
+            current_pos: 0,
+            file,
+        }
+    }
+}
+
+impl PlatformFile for File {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, PlatformFileError> {
+        let read = read_file(&self.file, self.current_pos, buf);
+        self.current_pos += read;
+        Ok(read)
+    }
+
+    fn seek_from_current(&mut self, offset: i64) -> Result<(), PlatformFileError> {
+        if offset.is_positive() {
+            self.current_pos += offset as usize;
+        } else {
+            self.current_pos -= offset as usize;
+        }
+        Ok(())
+    }
+
+    fn seek_from_start(&mut self, offset: usize) -> Result<(), PlatformFileError> {
+        self.current_pos = offset;
+        Ok(())
+    }
+
+    fn seek_from_end(&mut self, offset: usize) -> Result<(), PlatformFileError> {
+        self.current_pos = self.length() - offset;
+        Ok(())
+    }
+
+    fn length(&mut self) -> usize {
+        file_len(&self.file)
+    }
+}