diff --git a/src/modules/chips/atmega328p/atmega328p.zig b/src/modules/chips/atmega328p/atmega328p.zig
index 3e6b978..7192049 100644
--- a/src/modules/chips/atmega328p/atmega328p.zig
+++ b/src/modules/chips/atmega328p/atmega328p.zig
@@ -8,8 +8,14 @@ pub const memory_regions = [_]micro_linker.MemoryRegion{
     micro_linker.MemoryRegion{ .offset = 0x800100, .length = 2048, .kind = .ram },
 };
 
+const Port = enum(u8) {
+    B = 1,
+    C = 2,
+    D = 3,
+};
+
 pub fn parsePin(comptime spec: []const u8) type {
-    const invalid_format_msg = "The given pin '" ++ spec ++ "' has an invalid format. Pins must follow the format \"P{Port}.{Pin}\" scheme.";
+    const invalid_format_msg = "The given pin '" ++ spec ++ "' has an invalid format. Pins must follow the format \"P{Port}{Pin}\" scheme.";
 
     if (spec.len != 3)
         @compileError(invalid_format_msg);
@@ -17,31 +23,41 @@ pub fn parsePin(comptime spec: []const u8) type {
         @compileError(invalid_format_msg);
 
     return struct {
-        pub const port: u8 = std.ascii.toUpper(spec[1]) - 'A';
-        pub const pin: u3 = @intCast(u3, spec[2] - '0');
+        pub const port: Port = std.meta.stringToEnum(Port, spec[1..2]) orelse @compileError(invalid_format_msg);
+        pub const pin: u3 = std.fmt.parseInt(u3, spec[2..3], 10) catch @compileError(invalid_format_msg);
     };
 }
 
 pub const gpio = struct {
-    fn dirReg(comptime pin: type) *volatile u8 {
-        return @intToPtr(*volatile u8, 0x01);
-    }
-    fn portReg(comptime pin: type) *volatile u8 {
-        return @intToPtr(*volatile u8, 0x01);
-    }
-    fn pinReg(comptime pin: type) *volatile u8 {
-        return @intToPtr(*volatile u8, 0x01);
+    fn regs(comptime desc: type) type {
+        return struct {
+            const pin_addr = 3 * @enumToInt(desc.port) + 0x00;
+            const dir_addr = 3 * @enumToInt(desc.port) + 0x01;
+            const port_addr = 3 * @enumToInt(desc.port) + 0x02;
+
+            const pin = @intToPtr(*volatile u8, pin_addr);
+            const dir = @intToPtr(*volatile u8, dir_addr);
+            const port = @intToPtr(*volatile u8, port_addr);
+        };
     }
 
     pub fn setOutput(comptime pin: type) void {
-        dirReg(pin).* |= (1 << pin.pin);
+        asm volatile ("sbi %[port], %[pin]"
+            :
+            : [port] "I" (regs(pin).dir_addr),
+              [pin] "I" (pin.pin)
+        );
     }
     pub fn setInput(comptime pin: type) void {
-        dirReg(pin).* &= ~(@as(u8, 1) << pin.pin);
+        asm volatile ("cbi %[port], %[pin]"
+            :
+            : [port] "I" (regs(pin).dir_addr),
+              [pin] "I" (pin.pin)
+        );
     }
 
     pub fn read(comptime pin: type) u1 {
-        return if ((pinReg(pin).* & (1 << pin.pin)) != 0)
+        return if ((regs(pin).pin.* & (1 << pin.pin)) != 0)
             @as(u1, 1)
         else
             0;
@@ -49,13 +65,25 @@ pub const gpio = struct {
 
     pub fn write(comptime pin: type, state: u1) void {
         if (state == 1) {
-            portReg(pin).* |= (1 << pin.pin);
+            asm volatile ("sbi %[port], %[pin]"
+                :
+                : [port] "I" (regs(pin).port_addr),
+                  [pin] "I" (pin.pin)
+            );
         } else {
-            portReg(pin).* &= ~@as(u8, 1 << pin.pin);
+            asm volatile ("cbi %[port], %[pin]"
+                :
+                : [port] "I" (regs(pin).port_addr),
+                  [pin] "I" (pin.pin)
+            );
         }
     }
 
     pub fn toggle(comptime pin: type) void {
-        portReg(pin).* ^= (1 << pin.pin);
+        asm volatile ("sbi %[port], %[pin]"
+            :
+            : [port] "I" (regs(pin).pin_addr),
+              [pin] "I" (pin.pin)
+        );
     }
 };
diff --git a/tests/blinky.zig b/tests/blinky.zig
index 7b30cee..3dece30 100644
--- a/tests/blinky.zig
+++ b/tests/blinky.zig
@@ -30,8 +30,10 @@ pub fn main() void {
 }
 
 fn busyloop() void {
+    const limit = 100_000;
+
     var i: u24 = 0;
-    while (i < 100_000) : (i += 1) {
+    while (i < limit) : (i += 1) {
         @import("std").mem.doNotOptimizeAway(i);
     }
 }