From 79a5fde52dbb07382c96ff49f9324071a1b50eee Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=27vesim=27=20Kuli=C5=84ski?= <vesim809@pm.me>
Date: Sun, 14 Dec 2025 19:31:33 +0100
Subject: [PATCH] rp2xxx: Add I2S output implementation based on PIO

---
 port/raspberrypi/rp2xxx/src/extra.zig         |   1 +
 .../rp2xxx/src/extra/I2S_Output.zig           | 115 ++++++++++++++++++
 port/raspberrypi/rp2xxx/src/hal.zig           |   1 +
 3 files changed, 117 insertions(+)
 create mode 100644 port/raspberrypi/rp2xxx/src/extra.zig
 create mode 100644 port/raspberrypi/rp2xxx/src/extra/I2S_Output.zig

diff --git a/port/raspberrypi/rp2xxx/src/extra.zig b/port/raspberrypi/rp2xxx/src/extra.zig
new file mode 100644
index 000000000..23521bb7b
--- /dev/null
+++ b/port/raspberrypi/rp2xxx/src/extra.zig
@@ -0,0 +1 @@
+pub const I2S_Output = @import("extra/I2S_Output.zig");
diff --git a/port/raspberrypi/rp2xxx/src/extra/I2S_Output.zig b/port/raspberrypi/rp2xxx/src/extra/I2S_Output.zig
new file mode 100644
index 000000000..151545c00
--- /dev/null
+++ b/port/raspberrypi/rp2xxx/src/extra/I2S_Output.zig
@@ -0,0 +1,115 @@
+pub const I2S_Output = @This();
+
+pio: Pio,
+sm: StateMachine,
+
+sample_rate: u32,
+sample_size: u6,
+
+const program = blk: {
+    @setEvalBranchQuota(20_000);
+    break :blk pio_.assemble(
+        \\.program i2s_output
+        \\.side_set 2
+        \\
+        \\.wrap_target
+        \\;                              0bWB W - Word Clock B - Bit clock
+        \\    mov x, y              side 0b01
+        \\left_channel:
+        \\    out pins, 1           side 0b00
+        \\    jmp x-- left_channel  side 0b01
+        \\    out pins 1            side 0b10
+        \\    mov x, y              side 0b11
+        \\right_channel:
+        \\    out pins 1            side 0b10
+        \\    jmp x-- right_channel side 0b11
+        \\    out pins 1            side 0b00
+        \\.wrap
+    , .{}).get_program_by_name("i2s_output");
+};
+
+pub const InitConfig = struct {
+    clock_config: clocks.config.Global,
+    pio: Pio,
+    sm: StateMachine,
+
+    data_pin: Pin,
+    mclk_pin: Pin,
+    lrclk_pin: Pin,
+
+    sample_rate: u32 = 44100,
+    sample_size: u6 = 32,
+};
+
+pub fn init(config: InitConfig) !I2S_Output {
+    if (@intFromEnum(config.lrclk_pin) + 1 != @intFromEnum(config.mclk_pin)) return error.MclkNotAfterLrclk;
+
+    const sample_rate_multiplier: u32 = switch (config.sample_size) {
+        // 8, TODO: borked for some reasons
+        16 => 1,
+        // 24 => // TODO
+        32 => 2,
+        else => return error.InvalidSampleSize,
+    };
+
+    const system_frequency = config.clock_config.sys.?.frequency();
+    const divider = system_frequency * 4 / (config.sample_rate * sample_rate_multiplier);
+
+    try config.pio.sm_load_and_start_program(config.sm, program, .{
+        .clkdiv = .{ .int = @intCast(divider >> 8), .frac = @intCast(divider & 0xff) },
+        .pin_mappings = .{
+            .out = .single(config.data_pin),
+            .side_set = .{ .low = config.lrclk_pin, .high = config.mclk_pin },
+        },
+        .shift = .{
+            .out_shiftdir = .left,
+            .autopull = true,
+            .pull_threshold = if (config.sample_size == 32) 0 else @truncate(config.sample_size),
+            .join_tx = true,
+        },
+    });
+
+    // there are 2 instructions outside the loop
+    config.pio.sm_exec_set_y(config.sm, config.sample_size - 2);
+
+    try config.pio.sm_set_pindir(config.sm, config.lrclk_pin, 2, .out);
+    try config.pio.sm_set_pindir(config.sm, config.data_pin, 1, .out);
+    config.pio.sm_set_enabled(config.sm, true);
+
+    return I2S_Output{
+        .pio = config.pio,
+        .sm = config.sm,
+        .sample_rate = config.sample_rate,
+        .sample_size = config.sample_size,
+    };
+}
+
+pub fn dma_data_size(self: I2S_Output) DataSize {
+    return switch (self.sample_size) {
+        8 => .size_8,
+        16 => .size_16,
+        32 => .size_32,
+        else => unreachable,
+    };
+}
+
+pub inline fn write_sample(self: I2S_Output, sample: anytype) void {
+    switch (@TypeOf(sample)) {
+        i8, i16, i32 => {},
+        else => comptime unreachable,
+    }
+    std.debug.assert(@bitSizeOf(@TypeOf(sample)) == self.sample_size);
+
+    const tx_fifo: *volatile @TypeOf(sample) = @ptrCast(self.pio.sm_get_tx_fifo(self.sm));
+    tx_fifo.* = sample;
+}
+
+const std = @import("std");
+const clocks = @import("../hal/clocks.zig");
+const dma = @import("../hal/dma.zig");
+const DataSize = dma.DataSize;
+const gpio = @import("../hal/gpio.zig");
+const Pin = gpio.Pin;
+const pio_ = @import("../hal/pio.zig");
+const Pio = pio_.Pio;
+const StateMachine = pio_.StateMachine;
diff --git a/port/raspberrypi/rp2xxx/src/hal.zig b/port/raspberrypi/rp2xxx/src/hal.zig
index 5b0e39b78..7e4460e75 100644
--- a/port/raspberrypi/rp2xxx/src/hal.zig
+++ b/port/raspberrypi/rp2xxx/src/hal.zig
@@ -38,6 +38,7 @@ pub const time = @import("hal/time.zig");
 pub const uart = @import("hal/uart.zig");
 pub const usb = @import("hal/usb.zig");
 pub const watchdog = @import("hal/watchdog.zig");
+pub const extra = @import("extra.zig");
 
 comptime {
     // HACK: tests can't access microzig. maybe there's a better way to do this.