Read a button (edge events)

Detect button presses the right way: ask the kernel to watch the pin and wake your program only when the level actually changes — no busy-waiting in a while loop, and microsecond-accurate timestamps straight from the driver.

Wiring

GPIO27 ──┬── button ── GND
         │
   (internal/board pull-up holds it High; pressing pulls it Low)

Wire a push-button between GPIO27 and GND. Add an external pull-up resistor, or rely on the board default — WatchEdge itself sets no internal bias.

Code

namespace Demo

import Amalgame.Hardware

public class Program {
    public static void Main(string[] args) {
        let button: int = 27

        if (!Gpio.WatchEdge(button, Edge.Both)) {
            Console.WriteLine("could not watch GPIO27 — check permissions")
            return
        }
        Console.WriteLine("watching GPIO27 (10 edges then exit)…")

        var seen: int = 0
        while (seen < 10) {
            let ev: GpioEvent = Gpio.WaitEdge(5000)   // block up to 5s
            if (ev.IsTimeout()) {
                Console.WriteLine("(idle 5s)")
            } else {
                var what: string = "falling"
                if (ev.KindOf() == Edge.Rising) { what = "rising" }
                Console.WriteLine(what + " edge on GPIO" +
                                  String_FromInt(ev.PinOf()) + " @ " +
                                  String_FromInt(ev.TimestampNsOf()) + "ns")
                seen = seen + 1
            }
        }

        Gpio.Close()
    }
}

Run

amc build main.am -o button
./button

Press the button a few times; each press and release prints a line.

What's happening

• Gpio.WatchEdge(27, Edge.Both) arms kernel edge detection. Use Edge.Rising, Edge.Falling, or Edge.Both.
• Gpio.WaitEdge(5000) blocks (sleeping in the kernel, costing zero CPU) until the next edge, or up to 5000 ms. On timeout it returns a sentinel whose IsTimeout() is true.
• A delivered GpioEvent tells you KindOf() (Rising/Falling), PinOf(), and TimestampNsOf() (kernel monotonic nanoseconds).
• Prefer non-blocking draining? Gpio.PollEdges() returns a List<GpioEvent> of everything queued, oldest first, without waiting.

This is the interrupt-style pattern — far better than reading Gpio.DigitalRead(27) in a tight loop, which burns a core and can miss fast presses.

Next: scan an I²C bus →