langref: packed struct documentation

doc/langref/packed_struct_mmio.zig

@@ -0,0 +1,16 @@
+pub const GPIORegister = packed struct(u8) {
+    GPIO0: bool,
+    GPIO1: bool,
+    GPIO2: bool,
+    GPIO3: bool,
+    _reserved: u4 = 0,
+};
+
+/// Write a new state to the memory-mapped IO.
+pub fn writeToGPIO(new_states: GPIORegister) void {
+    const gpio_register_address = 0x0123;
+    const raw_ptr: *align(1) volatile GPIORegister = @ptrFromInt(gpio_register_address);
+    raw_ptr.* = new_states;
+}
+
+// syntax