Implements a generic gpio button driver with basic debouncing. (#41)

Co-authored-by: Felix "xq" Queißner <git@masterq32.de>

src/drivers/button.zig

@@ -0,0 +1,67 @@
+const std = @import("std");
+const micro = @import("microzig");
+
+pub const Event = enum {
+    /// Nothing has changed.
+    idle,
+
+    /// The button was pressed. Will only trigger once per press.
+    /// Use `Button.isPressed()` to check if the button is currently held.
+    pressed,
+
+    /// The button was released. Will only trigger once per release.
+    /// Use `Button.isPressed()` to check if the button is currently held.
+    released,
+};
+
+pub fn Button(
+    /// The GPIO pin the button is connected to. Will be initialized when calling Button.init
+    comptime gpio: type,
+    /// The active state for the button. Use `.high` for active-high, `.low` for active-low.
+    comptime active_state: micro.gpio.State,
+    /// Optional filter depth for debouncing. If `null` is passed, 16 samples are used to debounce the button, 
+    /// otherwise the given number of samples is used.
+    comptime filter_depth: ?comptime_int,
+) type {
+    return struct {
+        const Self = @This();
+        const DebounceFilter = std.meta.Int(.unsigned, filter_depth orelse 16);
+
+        debounce: DebounceFilter,
+        state: micro.gpio.State,
+
+        pub fn init() Self {
+            gpio.init();
+            return Self{
+                .debounce = 0,
+                .state = gpio.read(),
+            };
+        }
+
+        /// Polls for the button state. Returns the change event for the button if any.
+        pub fn poll(self: *Self) Event {
+            const state = gpio.read();
+            const active_unfiltered = (state == active_state);
+
+            const previous_debounce = self.debounce;
+            self.debounce <<= 1;
+            if (active_unfiltered) {
+                self.debounce |= 1;
+            }
+
+            if (active_unfiltered and previous_debounce == 0) {
+                return .pressed;
+            } else if (!active_unfiltered and self.debounce == 0 and previous_debounce != 0) {
+                return .released;
+            } else {
+                return .idle;
+            }
+        }
+
+        /// Returns `true` when the button is pressed.
+        /// Will only be updated when `poll` is regularly called.
+        pub fn isPressed(self: *Self) bool {
+            return (self.debounce != 0);
+        }
+    };
+}

src/main.zig

@@ -189,4 +189,10 @@ pub const drivers = struct {
         .path = .{ .path = root_path ++ "drivers/quadrature.zig" },
         .dependencies = &.{pkgs.microzig},
     };
+
+    pub const button = std.build.Pkg{
+        .name = "microzig.button",
+        .path = .{ .path = root_path ++ "drivers/button.zig" },
+        .dependencies = &.{pkgs.microzig},
+    };
 };