diff --git a/build.zig b/build.zig
index b395268..c9ca6c0 100644
--- a/build.zig
+++ b/build.zig
@@ -185,7 +185,7 @@ fn addEmbeddedExecutable(builder: *std.build.Builder, name: []const u8, source:
     //   - This requires building another tool that runs on the host that compiles those files and emits the linker script.
     //    - src/tools/linkerscript-gen.zig is the source file for this
 
-    exe.bundle_compiler_rt = false;
+    // exe.bundle_compiler_rt = false;
 
     switch (backing) {
         .chip => {
diff --git a/src/core/debug.zig b/src/core/debug.zig
new file mode 100644
index 0000000..eb2474c
--- /dev/null
+++ b/src/core/debug.zig
@@ -0,0 +1,38 @@
+const std = @import("std");
+const micro = @import("microzig.zig");
+
+pub fn busySleep(comptime limit: comptime_int) void {
+    if (limit <= 0) @compileError("limit must be non-negative!");
+
+    comptime var bits = 0;
+    inline while ((1 << bits) <= limit) {
+        bits += 1;
+    }
+
+    const I = std.meta.Int(.unsigned, bits);
+
+    var i: I = 0;
+    while (i < limit) : (i += 1) {
+        @import("std").mem.doNotOptimizeAway(i);
+    }
+}
+
+const DebugErr = error{};
+fn writerWrite(ctx: void, string: []const u8) DebugErr!usize {
+    write(string);
+    return string.len;
+}
+
+const DebugWriter = std.io.Writer(void, DebugErr, writerWrite);
+
+pub fn write(string: []const u8) void {
+    if (!micro.config.has_board)
+        return;
+    if (!@hasDecl(micro.board, "debugWrite"))
+        return;
+    micro.board.debugWrite(string);
+}
+
+pub fn writer() DebugWriter {
+    return DebugWriter{ .context = {} };
+}
diff --git a/src/core/gpio.zig b/src/core/gpio.zig
index bbbe57d..325cfed 100644
--- a/src/core/gpio.zig
+++ b/src/core/gpio.zig
@@ -57,12 +57,12 @@ pub fn Gpio(comptime pin: type, config: anytype) type {
         }
 
         fn read() State {
-            return @intToEnum(State, chip.gpio.read(pin.source_pin));
+            return chip.gpio.read(pin.source_pin);
         }
 
         // outputs:
         fn write(state: State) void {
-            chip.gpio.write(pin.source_pin, @enumToInt(state));
+            chip.gpio.write(pin.source_pin, state);
         }
 
         fn setToHigh() void {
diff --git a/src/core/microzig.zig b/src/core/microzig.zig
index 44ca0c9..4664fc5 100644
--- a/src/core/microzig.zig
+++ b/src/core/microzig.zig
@@ -30,13 +30,29 @@ pub const Pin = pin.Pin;
 pub const uart = @import("uart.zig");
 pub const Uart = uart.Uart;
 
+pub const debug = @import("debug.zig");
+
 /// The microzig panic handler. Will disable interrupts and loop endlessly.
 /// Export this symbol from your main file to enable microzig:
 /// ```
 /// const micro = @import("microzig");
 /// pub const panic = micro.panic;
 /// ```
-pub fn panic(message: []const u8, stack_trace: ?*std.builtin.StackTrace) noreturn {
+pub fn panic(message: []const u8, maybe_stack_trace: ?*std.builtin.StackTrace) noreturn {
+    var writer = debug.writer();
+    writer.print("microzig PANIC: {s}\r\n", .{message}) catch unreachable;
+    if (maybe_stack_trace) |stack_trace| {
+        var frame_index: usize = 0;
+        var frames_left: usize = std.math.min(stack_trace.index, stack_trace.instruction_addresses.len);
+
+        while (frames_left != 0) : ({
+            frames_left -= 1;
+            frame_index = (frame_index + 1) % stack_trace.instruction_addresses.len;
+        }) {
+            const return_address = stack_trace.instruction_addresses[frame_index];
+            writer.print("0x{X:0>8}\r\n", .{return_address}) catch unreachable;
+        }
+    }
     hang();
 }
 
diff --git a/src/core/mmio.zig b/src/core/mmio.zig
index d6cdf41..a46ca0c 100644
--- a/src/core/mmio.zig
+++ b/src/core/mmio.zig
@@ -24,11 +24,14 @@ pub fn MMIO(comptime size: u8, comptime PackedT: type) type {
         pub const underlying_type = PackedT;
 
         pub fn read(addr: *volatile Self) PackedT {
-            return @bitCast(PackedT, addr.*);
+            return @bitCast(PackedT, addr.raw);
         }
 
         pub fn write(addr: *volatile Self, val: PackedT) void {
-            addr.* = @bitCast(IntT, val);
+            // This is a workaround for a compiler bug related to miscompilation
+            // If the tmp var is not used, result location will fuck things up
+            var tmp = @bitCast(IntT, val);
+            addr.raw = tmp;
         }
 
         pub fn modify(addr: *volatile Self, fields: anytype) void {
diff --git a/src/core/pin.zig b/src/core/pin.zig
index c7c5db4..b46962e 100644
--- a/src/core/pin.zig
+++ b/src/core/pin.zig
@@ -28,7 +28,7 @@ pub fn Pin(comptime spec: []const u8) type {
         pub const source_pin = pin;
 
         pub fn route(target: pin.Targets) void {
-            unreachable;
+            chip.routePin(source_pin, target);
         }
     };
 }
diff --git a/src/modules/boards/mbed-lpc1768/mbed-lpc1768.zig b/src/modules/boards/mbed-lpc1768/mbed-lpc1768.zig
index 4994c7f..95358ff 100644
--- a/src/modules/boards/mbed-lpc1768/mbed-lpc1768.zig
+++ b/src/modules/boards/mbed-lpc1768/mbed-lpc1768.zig
@@ -1,4 +1,35 @@
 pub const chip = @import("chip");
+pub const micro = @import("microzig");
+
+pub fn debugWrite(string: []const u8) void {
+    const clk_pin = micro.Pin("DIP5");
+    const dat_pin = micro.Pin("DIP6");
+
+    const clk = micro.Gpio(clk_pin, .{ .mode = .output, .initial_state = .low });
+    const dat = micro.Gpio(dat_pin, .{ .mode = .output, .initial_state = .low });
+
+    clk.init();
+    dat.init();
+
+    micro.debug.busySleep(1_000);
+
+    for (string) |c| {
+        comptime var i: usize = 128;
+        inline while (i > 0) : (i = i >> 1) {
+            if ((c & i) != 0) {
+                dat.write(.high);
+            } else {
+                dat.write(.low);
+            }
+            clk.write(.high);
+            micro.debug.busySleep(1_000);
+            clk.write(.low);
+            micro.debug.busySleep(1_000);
+        }
+    }
+    dat.write(.low);
+    clk.write(.low);
+}
 
 pub const pin_map = .{
     // Onboard-LEDs
diff --git a/src/modules/chips/lpc1768/lpc1768.zig b/src/modules/chips/lpc1768/lpc1768.zig
index 5d56401..d03809e 100644
--- a/src/modules/chips/lpc1768/lpc1768.zig
+++ b/src/modules/chips/lpc1768/lpc1768.zig
@@ -11,6 +11,13 @@ pub const memory_regions = [_]micro_linker.MemoryRegion{
     micro_linker.MemoryRegion{ .offset = 0x2007C000, .length = 32 * 1024, .kind = .ram },
 };
 
+pub const PinTarget = enum(u2) {
+    func00 = 0b00,
+    func01 = 0b01,
+    func10 = 0b10,
+    func11 = 0b11,
+};
+
 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.";
     if (spec[0] != 'P')
@@ -18,12 +25,17 @@ pub fn parsePin(comptime spec: []const u8) type {
 
     const index = std.mem.indexOfScalar(u8, spec, '.') orelse @compileError(invalid_format_msg);
 
-    const _port: u3 = std.fmt.parseInt(u3, spec[1..index], 10) catch @compileError(invalid_format_msg);
-    const _pin: u5 = std.fmt.parseInt(u5, spec[index + 1 ..], 10) catch @compileError(invalid_format_msg);
+    const _port: comptime_int = std.fmt.parseInt(u3, spec[1..index], 10) catch @compileError(invalid_format_msg);
+    const _pin: comptime_int = std.fmt.parseInt(u5, spec[index + 1 ..], 10) catch @compileError(invalid_format_msg);
+
+    const sel_reg_name = std.fmt.comptimePrint("PINSEL{d}", .{(2 * _port + _pin / 16)});
 
     const _regs = struct {
         const name_suffix = std.fmt.comptimePrint("{d}", .{_port});
 
+        const pinsel_reg = @field(registers.PINCONNECT, sel_reg_name);
+        const pinsel_field = std.fmt.comptimePrint("P{d}_{d}", .{ _port, _pin });
+
         const dir = @field(registers.GPIO, "DIR" ++ name_suffix);
         const pin = @field(registers.GPIO, "PIN" ++ name_suffix);
         const set = @field(registers.GPIO, "SET" ++ name_suffix);
@@ -32,13 +44,21 @@ pub fn parsePin(comptime spec: []const u8) type {
     };
 
     return struct {
-        pub const port = _port;
-        pub const pin = _pin;
+        pub const port: u3 = _port;
+        pub const pin: u5 = _pin;
         pub const regs = _regs;
         const gpio_mask: u32 = (1 << pin);
+
+        pub const Targets = PinTarget;
     };
 }
 
+pub fn routePin(comptime pin: type, function: PinTarget) void {
+    var val = pin.regs.pinsel_reg.read();
+    @field(val, pin.regs.pinsel_field) = @enumToInt(function);
+    pin.regs.pinsel_reg.write(val);
+}
+
 pub const gpio = struct {
     pub fn setOutput(comptime pin: type) void {
         pin.regs.dir.raw |= pin.gpio_mask;
@@ -47,15 +67,15 @@ pub const gpio = struct {
         pin.regs.dir.raw &= ~pin.gpio_mask;
     }
 
-    pub fn read(comptime pin: type) u1 {
+    pub fn read(comptime pin: type) micro.gpio.State {
         return if ((pin.regs.pin.raw & pin.gpio_mask) != 0)
-            @as(u1, 1)
+            micro.gpio.State.high
         else
-            0;
+            micro.gpio.State.low;
     }
 
-    pub fn write(comptime pin: type, state: u1) void {
-        if (state == 1) {
+    pub fn write(comptime pin: type, state: micro.gpio.State) void {
+        if (state == .high) {
             pin.regs.set.raw = pin.gpio_mask;
         } else {
             pin.regs.clr.raw = pin.gpio_mask;
@@ -75,6 +95,7 @@ pub fn Uart(comptime index: usize) type {
         const Self = @This();
 
         pub fn init(config: micro.uart.Config) !Self {
+            micro.debug.write("0");
             switch (index) {
                 0 => {
                     registers.SYSCON.PCONP.modify(.{ .PCUART0 = true });
@@ -94,6 +115,7 @@ pub fn Uart(comptime index: usize) type {
                 },
                 else => unreachable,
             }
+            micro.debug.write("1");
 
             UARTn.LCR.write(.{
                 // 8N1
@@ -118,8 +140,14 @@ pub fn Uart(comptime index: usize) type {
                 .BC = false,
                 .DLAB = true,
             });
+            micro.debug.write("2");
             UARTn.FCR.modify(.{ .FIFOEN = false });
 
+            micro.debug.writer().print("clock: {} baud: {} ", .{
+                micro.clock.get(),
+                config.baud_rate,
+            }) catch {};
+
             const pclk = micro.clock.get() / 4;
             const divider = (pclk / (16 * config.baud_rate));
 
diff --git a/src/modules/cpus/cortex-m3/cortex-m3.zig b/src/modules/cpus/cortex-m3/cortex-m3.zig
index 4c82311..29c1414 100644
--- a/src/modules/cpus/cortex-m3/cortex-m3.zig
+++ b/src/modules/cpus/cortex-m3/cortex-m3.zig
@@ -1,49 +1,42 @@
 const std = @import("std");
 
 pub fn sei() void {
-    __enable_irq();
+    asm volatile ("cpsie i");
 }
 
 pub fn cli() void {
-    __disable_irq();
-}
-
-pub fn __enable_irq() void {
-    asm volatile ("cpsie i");
-}
-pub fn __disable_irq() void {
     asm volatile ("cpsid i");
 }
 
-pub fn __enable_fault_irq() void {
+pub fn enable_fault_irq() void {
     asm volatile ("cpsie f");
 }
-pub fn __disable_fault_irq() void {
+pub fn disable_fault_irq() void {
     asm volatile ("cpsid f");
 }
 
-pub fn __NOP() void {
+pub fn nop() void {
     asm volatile ("nop");
 }
-pub fn __WFI() void {
+pub fn wfi() void {
     asm volatile ("wfi");
 }
-pub fn __WFE() void {
+pub fn wfe() void {
     asm volatile ("wfe");
 }
-pub fn __SEV() void {
+pub fn sev() void {
     asm volatile ("sev");
 }
-pub fn __ISB() void {
+pub fn isb() void {
     asm volatile ("isb");
 }
-pub fn __DSB() void {
+pub fn dsb() void {
     asm volatile ("dsb");
 }
-pub fn __DMB() void {
+pub fn dmb() void {
     asm volatile ("dmb");
 }
-pub fn __CLREX() void {
+pub fn clrex() void {
     asm volatile ("clrex");
 }
 
@@ -53,11 +46,11 @@ pub const startup_logic = struct {
     const VectorTable = extern struct {
         initial_stack_pointer: u32,
         reset: InterruptVector,
-        nmi: InterruptVector = unhandledInterrupt,
-        hard_fault: InterruptVector = unhandledInterrupt,
-        mpu_fault: InterruptVector = unhandledInterrupt,
-        bus_fault: InterruptVector = unhandledInterrupt,
-        usage_fault: InterruptVector = unhandledInterrupt,
+        nmi: InterruptVector = makeUnhandledHandler("nmi"),
+        hard_fault: InterruptVector = makeUnhandledHandler("hard_fault"),
+        mpu_fault: InterruptVector = makeUnhandledHandler("mpu_fault"),
+        bus_fault: InterruptVector = makeUnhandledHandler("bus_fault"),
+        usage_fault: InterruptVector = makeUnhandledHandler("usage_fault"),
 
         reserved: u32 = 0,
     };
@@ -68,8 +61,12 @@ pub const startup_logic = struct {
         .reset = _start,
     };
 
-    fn unhandledInterrupt() callconv(.C) noreturn {
-        @panic("unhandled interrupt");
+    fn makeUnhandledHandler(comptime str: []const u8) fn () callconv(.C) noreturn {
+        return struct {
+            fn unhandledInterrupt() callconv(.C) noreturn {
+                @panic("unhandled interrupt: " ++ str);
+            }
+        }.unhandledInterrupt;
     }
 
     extern fn microzig_main() noreturn;
diff --git a/tests/uart-sync.zig b/tests/uart-sync.zig
index 7b61086..7116272 100644
--- a/tests/uart-sync.zig
+++ b/tests/uart-sync.zig
@@ -7,25 +7,116 @@ pub const panic = micro.panic;
 const uart_txd_pin = micro.Pin("P0.15");
 const uart_rxd_pin = micro.Pin("P0.16");
 
-pub const cpu_frequency: u32 = 10_000_000; // 10 MHz
+const debug_pin = micro.Pin("P0.17");
+
+const led1_pin = micro.Pin("P1.18");
+const led2_pin = micro.Pin("P1.20");
+const led3_pin = micro.Pin("P1.21");
+const led4_pin = micro.Pin("P1.23");
+
+pub const cpu_frequency: u32 = 100_000_000; // 100 MHz
+
+const PLL = struct {
+    fn init() void {
+        reset_overclocking();
+    }
+
+    fn reset_overclocking() void {
+        overclock_flash(5); // 5 cycles access time
+        overclock_pll(3); // 100 MHz
+    }
+
+    fn overclock_flash(timing: u5) void {
+        micro.chip.registers.SYSCON.FLASHCFG.write(.{
+            .FLASHTIM = @intCast(u4, timing - 1),
+        });
+    }
+    fn feed_pll() callconv(.Inline) void {
+        micro.chip.registers.SYSCON.PLL0FEED.write(.{ .PLL0FEED = 0xAA });
+        micro.chip.registers.SYSCON.PLL0FEED.write(.{ .PLL0FEED = 0x55 });
+    }
+
+    fn overclock_pll(divider: u8) void {
+        // PLL einrichten für RC
+        micro.chip.registers.SYSCON.PLL0CON.write(.{
+            .PLLE0 = false,
+            .PLLC0 = false,
+        });
+        feed_pll();
+
+        micro.chip.registers.SYSCON.CLKSRCSEL.write(.{ .CLKSRC = 0 }); // RC-Oszillator als Quelle
+        micro.chip.registers.SYSCON.PLL0CFG.write(.{
+            // SysClk = (4MHz / 2) * (2 * 75) = 300 MHz
+            .MSEL0 = 74,
+            .NSEL0 = 1,
+        });
+        // CPU Takt = SysClk / divider
+        micro.chip.registers.SYSCON.CCLKCFG.write(.{ .CCLKSEL = divider - 1 });
+
+        feed_pll();
+
+        micro.chip.registers.SYSCON.PLL0CON.modify(.{ .PLLE0 = true }); // PLL einschalten
+        feed_pll();
+
+        var i: usize = 0;
+        while (i < 1_000) : (i += 1) {
+            micro.cpu.nop();
+        }
+
+        micro.chip.registers.SYSCON.PLL0CON.modify(.{ .PLLC0 = true });
+        feed_pll();
+    }
+};
 
 pub fn main() !void {
-    var debug_port = try micro.Uart(0).init(.{
+    const gpio_init = .{ .mode = .output, .initial_state = .low };
+
+    const led1 = micro.Gpio(led1_pin, gpio_init);
+    const led2 = micro.Gpio(led2_pin, gpio_init);
+    const led3 = micro.Gpio(led3_pin, gpio_init);
+    const led4 = micro.Gpio(led4_pin, gpio_init);
+
+    const status = micro.Gpio(debug_pin, .{
+        .mode = .output,
+        .initial_state = .high,
+    });
+    status.init();
+    led1.init();
+    led2.init();
+    led3.init();
+    led4.init();
+
+    uart_txd_pin.route(.func01);
+    uart_rxd_pin.route(.func01);
+
+    PLL.init();
+    led1.setToHigh();
+
+    var debug_port = micro.Uart(1).init(.{
         .baud_rate = 9600,
         .stop_bits = .one,
         .parity = .none, // { none, even, odd, mark, space }
         .data_bits = .@"8", // 5, 6, 7, 8, or 9 data bits
-    });
+    }) catch |err| {
+        led1.write(if (err == error.UnsupportedBaudRate) micro.gpio.State.low else .high);
+        led2.write(if (err == error.UnsupportedParity) micro.gpio.State.low else .high);
+        led3.write(if (err == error.UnsupportedStopBitCount) micro.gpio.State.low else .high);
+        led4.write(if (err == error.UnsupportedWordSize) micro.gpio.State.low else .high);
+
+        micro.hang();
+    };
+    led2.setToHigh();
 
     var out = debug_port.writer();
     var in = debug_port.reader();
 
     try out.writeAll("Please enter a sentence:\r\n");
 
+    led3.setToHigh();
+
     while (true) {
-        try out.writeAll("> ");
-        var line_buffer: [64]u8 = undefined;
-        const line = (try in.readUntilDelimiterOrEof(&line_buffer, '\r')).?;
-        try out.writeAll(line);
+        try out.writeAll(".");
+        led4.toggle();
+        micro.debug.busySleep(100_000);
     }
 }