diff --git a/src/hal/adc.zig b/src/hal/adc.zig
index 2f6b96b..a77b102 100644
--- a/src/hal/adc.zig
+++ b/src/hal/adc.zig
@@ -5,9 +5,8 @@ const assert = std.debug.assert;
 
 const microzig = @import("microzig");
 const ADC = microzig.chip.peripherals.ADC;
-const rp2040 = microzig.hal;
-const gpio = rp2040.gpio;
-const resets = rp2040.resets;
+const gpio = @import("gpio.zig");
+const resets = @import("resets.zig");
 
 pub const temperature_sensor = struct {
     pub inline fn init() void {
diff --git a/src/hal/clocks.zig b/src/hal/clocks.zig
index 4a49809..b13ebd3 100644
--- a/src/hal/clocks.zig
+++ b/src/hal/clocks.zig
@@ -1,7 +1,6 @@
 const std = @import("std");
 
 const pll = @import("pll.zig");
-const util = @import("util.zig");
 const assert = std.debug.assert;
 
 // TODO: remove
diff --git a/src/hal/gpio.zig b/src/hal/gpio.zig
index 02f421e..53d3b0b 100644
--- a/src/hal/gpio.zig
+++ b/src/hal/gpio.zig
@@ -63,7 +63,7 @@ pub const Enabled = enum {
     enabled,
 };
 
-pub const PullUpDown = enum {
+pub const Pull = enum {
     up,
     down,
 };
@@ -76,12 +76,45 @@ pub fn num(n: u5) Pin {
 }
 
 pub fn mask(m: u32) Mask {
-    _ = m;
-    @panic("TODO");
+    return @intToEnum(Mask, m);
 }
 
 pub const Mask = enum(u30) {
     _,
+
+    pub fn set_function(self: Mask, function: Function) void {
+        const raw_mask = @enumToInt(self);
+        for (0..@bitSizeOf(Mask)) |i| {
+            const bit = @intCast(u5, i);
+            if (0 != raw_mask & (@as(u32, 1) << bit))
+                num(bit).set_function(function);
+        }
+    }
+
+    pub fn set_direction(self: Mask, direction: Direction) void {
+        const raw_mask = @enumToInt(self);
+        switch (direction) {
+            .out => SIO.GPIO_OE_SET.raw = raw_mask,
+            .in => SIO.GPIO_OE_CLR.raw = raw_mask,
+        }
+    }
+
+    pub fn set_pull(self: Mask, pull: ?Pull) void {
+        const raw_mask = @enumToInt(self);
+        for (0..@bitSizeOf(Mask)) |i| {
+            const bit = @intCast(u5, i);
+            if (0 != raw_mask & (@as(u32, 1) << bit))
+                num(bit).set_pull(pull);
+        }
+    }
+
+    pub fn put(self: Mask, value: u32) void {
+        SIO.GPIO_OUT_XOR.raw = (SIO.GPIO_OUT.raw ^ value) & @enumToInt(self);
+    }
+
+    pub fn read(self: Mask) u32 {
+        return SIO.GPIO_IN.raw & @enumToInt(self);
+    }
 };
 
 pub const Pin = enum(u5) {
@@ -134,12 +167,12 @@ pub const Pin = enum(u5) {
         return @as(u32, 1) << @enumToInt(gpio);
     }
 
-    pub inline fn set_pull(gpio: Pin, mode: ?PullUpDown) void {
+    pub inline fn set_pull(gpio: Pin, pull: ?Pull) void {
         const pads_reg = gpio.get_pads_reg();
 
-        if (mode == null) {
+        if (pull == null) {
             pads_reg.modify(.{ .PUE = 0, .PDE = 0 });
-        } else switch (mode.?) {
+        } else switch (pull.?) {
             .up => pads_reg.modify(.{ .PUE = 1, .PDE = 0 }),
             .down => pads_reg.modify(.{ .PUE = 0, .PDE = 1 }),
         }
@@ -171,6 +204,11 @@ pub const Pin = enum(u5) {
             0;
     }
 
+    pub inline fn set_input_enabled(pin: Pin, enabled: bool) void {
+        const pads_reg = pin.get_pads_reg();
+        pads_reg.modify(.{ .IE = @boolToInt(enabled) });
+    }
+
     pub inline fn set_function(gpio: Pin, function: Function) void {
         const pads_reg = gpio.get_pads_reg();
         pads_reg.modify(.{
@@ -193,33 +231,4 @@ pub const Pin = enum(u5) {
             .padding = 0,
         });
     }
-
-    //pub fn set_drive_strength(gpio: Gpio, drive: DriveStrength) void {
-    //    _ = drive;
-    //    const pads_reg = gpio.get_pads_reg();
-    //    pads_reg.modify(.{
-    //        .DRIVE = .{
-    //            .value = .@"12mA",
-    //        },
-    //    });
-    //}
 };
-
-// setting both uplls enables a "bus keep" function, a weak pull to whatever
-// is current high/low state of GPIO
-//pub fn setPulls(gpio: u32, up: bool, down: bool) void {}
-//
-//pub fn pullUp(gpio: u32) void {}
-//
-//pub fn pullDown(gpio: u32) void {}
-//pub fn disablePulls(gpio: u32) void {}
-//pub fn setIrqOver(gpio: u32, value: u32) void {}
-//pub fn setOutOver(gpio: u32, value: u32) void {}
-//pub fn setInOver(gpio: u32, value: u32) void {}
-//pub fn setOeOver(gpio: u32, value: u32) void {}
-//pub fn setInputEnabled(gpio: u32, enabled: Enabled) void {}
-//pub fn setinputHysteresisEnabled(gpio: u32, enabled: Enabled) void {}
-//pub fn setSlewRate(gpio: u32, slew_rate: SlewRate) void {}
-
-//pub fn setIrqEnabled(gpio: u32, events: IrqEvents) void {}
-//pub fn acknowledgeIrq(gpio: u32, events: IrqEvents) void {}
diff --git a/src/hal/hw.zig b/src/hal/hw.zig
index 1017c8a..89aee45 100644
--- a/src/hal/hw.zig
+++ b/src/hal/hw.zig
@@ -19,16 +19,16 @@ const xor_bits = @as(u32, 0x1) << 12;
 const set_bits = @as(u32, 0x2) << 12;
 const clear_bits = @as(u32, 0x3) << 12;
 
-pub fn clear_alias_raw(ptr: anytype) *u32 {
-    return @intToPtr(*u32, @ptrToInt(ptr) | clear_bits);
+pub fn clear_alias_raw(ptr: anytype) *volatile u32 {
+    return @intToPtr(*volatile u32, @ptrToInt(ptr) | clear_bits);
 }
 
-pub fn set_alias_raw(ptr: anytype) *u32 {
-    return @intToPtr(*u32, @ptrToInt(ptr) | set_bits);
+pub fn set_alias_raw(ptr: anytype) *volatile u32 {
+    return @intToPtr(*volatile u32, @ptrToInt(ptr) | set_bits);
 }
 
-pub fn xor_alias_raw(ptr: anytype) *u32 {
-    return @intToPtr(*u32, @ptrToInt(ptr) | xor_bits);
+pub fn xor_alias_raw(ptr: anytype) *volatile u32 {
+    return @intToPtr(*volatile u32, @ptrToInt(ptr) | xor_bits);
 }
 
 pub fn clear_alias(ptr: anytype) @TypeOf(ptr) {
@@ -42,3 +42,7 @@ pub fn set_alias(ptr: anytype) @TypeOf(ptr) {
 pub fn xor_alias(ptr: anytype) @TypeOf(ptr) {
     return @intToPtr(@TypeOf(ptr), @ptrToInt(ptr) | xor_bits);
 }
+
+pub inline fn tight_loop_contents() void {
+    asm volatile ("" ::: "memory");
+}
diff --git a/src/hal/pins.zig b/src/hal/pins.zig
index 1746409..f232092 100644
--- a/src/hal/pins.zig
+++ b/src/hal/pins.zig
@@ -48,7 +48,7 @@ pub const Pin = enum {
         function: Function = .SIO,
         direction: ?gpio.Direction = null,
         drive_strength: ?gpio.DriveStrength = null,
-        pull: ?gpio.PullUpDown = null,
+        pull: ?gpio.Pull = null,
         slew_rate: ?gpio.SlewRate = null,
         // input/output enable
         // schmitt trigger
diff --git a/src/hal/spi.zig b/src/hal/spi.zig
index 7170600..ee02131 100644
--- a/src/hal/spi.zig
+++ b/src/hal/spi.zig
@@ -8,7 +8,7 @@ const gpio = @import("gpio.zig");
 const clocks = @import("clocks.zig");
 const resets = @import("resets.zig");
 const time = @import("time.zig");
-const util = @import("util.zig");
+const hw = @import("hw.zig");
 
 const SpiRegs = microzig.chip.types.peripherals.SPI0;
 
@@ -101,7 +101,7 @@ pub const SPI = enum(u1) {
         // push-on-full, but continues shifting. Safe if SSPIMSC_RORIM is not set.
         for (src) |s| {
             while (!spi.is_writable()) {
-                util.tight_loop_contents();
+                hw.tight_loop_contents();
             }
             spi_regs.SSPDR.write_raw(s);
         }
@@ -111,7 +111,7 @@ pub const SPI = enum(u1) {
             _ = spi_regs.SSPDR.read();
         }
         while (spi_regs.SSPSR.read().BSY == 1) {
-            util.tight_loop_contents();
+            hw.tight_loop_contents();
         }
         while (spi.is_readable()) {
             _ = spi_regs.SSPDR.read();
diff --git a/src/hal/util.zig b/src/hal/util.zig
deleted file mode 100644
index 4f0d71c..0000000
--- a/src/hal/util.zig
+++ /dev/null
@@ -1,18 +0,0 @@
-pub fn xor_alias(ptr: anytype) @TypeOf(ptr) {
-    const xor_addr = @ptrToInt(ptr) | (1 << 12);
-    return @ptrCast(@TypeOf(ptr), xor_addr);
-}
-
-pub fn set_alias(ptr: anytype) @TypeOf(ptr) {
-    const set_addr = @ptrToInt(ptr) | (2 << 12);
-    return @ptrCast(@TypeOf(ptr), set_addr);
-}
-
-pub fn clear_alias(ptr: anytype) @TypeOf(ptr) {
-    const clear_addr = @ptrToInt(ptr) | (3 << 12);
-    return @ptrCast(@TypeOf(ptr), clear_addr);
-}
-
-pub inline fn tight_loop_contents() void {
-    asm volatile ("" ::: "memory");
-}