feat(cpu): implement thumb push / pop and stub format 13 thumb instrs

src/cpu/thumb/format13.zig

@@ -0,0 +1,13 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format13(comptime _: bool) InstrFn {
+    return struct {
+        fn inner(_: *Arm7tdmi, _: *Bus, _: u16) void {
+            std.debug.panic("[CPU|THUMB|Fmt13] Implement Format 13 THUMB Instructions", .{});
+        }
+    }.inner;
+}

src/cpu/thumb/format14.zig

@@ -0,0 +1,50 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format14(comptime L: bool, comptime R: bool) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u16) void {
+            var address: u32 = undefined;
+            if (L) {
+                // POP
+                address = cpu.r[13];
+
+                var i: usize = 0;
+                while (i < 8) : (i += 1) {
+                    if ((opcode >> @truncate(u3, i)) & 1 == 1) {
+                        cpu.r[i] = bus.read32(address);
+                        address += 4;
+                    }
+                }
+
+                if (R) {
+                    const value = bus.read32(address);
+                    cpu.r[15] = value & 0xFFFF_FFFE;
+                    address += 4;
+                }
+            } else {
+                address = cpu.r[13] - 4;
+
+                if (R) {
+                    bus.write32(address, cpu.r[14]);
+                    address -= 4;
+                }
+
+                var i: usize = 8;
+                while (i > 0) : (i -= 1) {
+                    const j = i - 1;
+
+                    if ((opcode >> @truncate(u3, j)) & 1 == 1) {
+                        bus.write32(address, cpu.r[j]);
+                        address -= 4;
+                    }
+                }
+            }
+
+            cpu.r[13] = address;
+        }
+    }.inner;
+}