feat: implement ARM7TDMI (and stub ARM946E-S)

lib/bitfield.zig

@@ -0,0 +1,146 @@
+const std = @import("std");
+
+fn PtrCastPreserveCV(comptime T: type, comptime PtrToT: type, comptime NewT: type) type {
+    return switch (PtrToT) {
+        *T => *NewT,
+        *const T => *const NewT,
+        *volatile T => *volatile NewT,
+        *const volatile T => *const volatile NewT,
+
+        else => @compileError("wtf you doing"),
+    };
+}
+
+fn BitType(comptime FieldType: type, comptime ValueType: type, comptime shamt: usize) type {
+    const self_bit: FieldType = (1 << shamt);
+
+    return extern struct {
+        bits: Bitfield(FieldType, shamt, 1),
+
+        pub fn set(self: anytype) void {
+            self.bits.field().* |= self_bit;
+        }
+
+        pub fn unset(self: anytype) void {
+            self.bits.field().* &= ~self_bit;
+        }
+
+        pub fn read(self: anytype) ValueType {
+            return @bitCast(ValueType, @truncate(u1, self.bits.field().* >> shamt));
+        }
+
+        // Since these are mostly used with MMIO, I want to avoid
+        // reading the memory just to write it again, also races
+        pub fn write(self: anytype, val: ValueType) void {
+            if (@bitCast(bool, val)) {
+                self.set();
+            } else {
+                self.unset();
+            }
+        }
+    };
+}
+
+// Original Bit Constructor
+// pub fn Bit(comptime FieldType: type, comptime shamt: usize) type {
+//     return BitType(FieldType, u1, shamt);
+// }
+
+pub fn Bit(comptime FieldType: type, comptime shamt: usize) type {
+    return BitType(FieldType, bool, shamt);
+}
+
+fn Boolean(comptime FieldType: type, comptime shamt: usize) type {
+    return BitType(FieldType, bool, shamt);
+}
+
+pub fn Bitfield(comptime FieldType: type, comptime shamt: usize, comptime num_bits: usize) type {
+    if (shamt + num_bits > @bitSizeOf(FieldType)) {
+        @compileError("bitfield doesn't fit");
+    }
+
+    const self_mask: FieldType = ((1 << num_bits) - 1) << shamt;
+
+    const ValueType = std.meta.Int(.unsigned, num_bits);
+
+    return extern struct {
+        dummy: FieldType,
+
+        fn field(self: anytype) PtrCastPreserveCV(@This(), @TypeOf(self), FieldType) {
+            return @ptrCast(PtrCastPreserveCV(@This(), @TypeOf(self), FieldType), self);
+        }
+
+        pub fn write(self: anytype, val: ValueType) void {
+            self.field().* &= ~self_mask;
+            self.field().* |= @intCast(FieldType, val) << shamt;
+        }
+
+        pub fn read(self: anytype) ValueType {
+            const val: FieldType = self.field().*;
+            return @intCast(ValueType, (val & self_mask) >> shamt);
+        }
+    };
+}
+
+test "bit" {
+    const S = extern union {
+        low: Bit(u32, 0),
+        high: Bit(u32, 1),
+        val: u32,
+    };
+
+    std.testing.expect(@sizeOf(S) == 4);
+    std.testing.expect(@bitSizeOf(S) == 32);
+
+    var s: S = .{ .val = 1 };
+
+    std.testing.expect(s.low.read() == 1);
+    std.testing.expect(s.high.read() == 0);
+
+    s.low.write(0);
+    s.high.write(1);
+
+    std.testing.expect(s.val == 2);
+}
+
+test "boolean" {
+    const S = extern union {
+        low: Boolean(u32, 0),
+        high: Boolean(u32, 1),
+        val: u32,
+    };
+
+    std.testing.expect(@sizeOf(S) == 4);
+    std.testing.expect(@bitSizeOf(S) == 32);
+
+    var s: S = .{ .val = 2 };
+
+    std.testing.expect(s.low.read() == false);
+    std.testing.expect(s.high.read() == true);
+
+    s.low.write(true);
+    s.high.write(false);
+
+    std.testing.expect(s.val == 1);
+}
+
+test "bitfield" {
+    const S = extern union {
+        low: Bitfield(u32, 0, 16),
+        high: Bitfield(u32, 16, 16),
+        val: u32,
+    };
+
+    std.testing.expect(@sizeOf(S) == 4);
+    std.testing.expect(@bitSizeOf(S) == 32);
+
+    var s: S = .{ .val = 0x13376969 };
+
+    std.testing.expect(s.low.read() == 0x6969);
+    std.testing.expect(s.high.read() == 0x1337);
+
+    s.low.write(0x1337);
+    s.high.write(0x6969);
+
+    std.testing.expect(s.val == 0x69691337);
+}