add a basic structure for disassembler + executor

Instructions added
Branch and Exchange (BX)
Branch and Link (B)
Multiply and Accumulate (MUL, MLA)
Multiply Long and Accumulate (SMULL, SMLAL, UMULL, UMLAL)
Single data swap (SWP)
[WIP] Halfword Transfer (STRH, LDRH)

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

include/bus.hh

@@ -0,0 +1 @@
+../src/bus.hh

include/cpu/cpu.hh

@@ -0,0 +1 @@
+../../src/cpu/cpu.hh

include/cpu/meson.build

@@ -0,0 +1,5 @@
+headers += files(
+  'cpu.hh',
+  'psr.hh',
+  'utility.hh'
+)

include/cpu/psr.hh

@@ -0,0 +1 @@
+../../src/cpu/psr.hh

include/cpu/utility.hh

@@ -0,0 +1,73 @@
+#pragma once
+
+#include <fmt/ostream.h>
+#include <ostream>
+
+static constexpr size_t ARM_INSTRUCTION_SIZE   = 4;
+static constexpr size_t THUMB_INSTRUCTION_SIZE = 2;
+
+enum class Mode {
+    /* M[4:0] in PSR */
+    User       = 0b10000,
+    Fiq        = 0b10001,
+    Irq        = 0b10010,
+    Supervisor = 0b10011,
+    Abort      = 0b10111,
+    Undefined  = 0b11011,
+    System     = 0b11111,
+};
+
+enum class State {
+    Arm   = 0,
+    Thumb = 1
+};
+
+enum class Condition {
+    EQ = 0b0000,
+    NE = 0b0001,
+    CS = 0b0010,
+    CC = 0b0011,
+    MI = 0b0100,
+    PL = 0b0101,
+    VS = 0b0110,
+    VC = 0b0111,
+    HI = 0b1000,
+    LS = 0b1001,
+    GE = 0b1010,
+    LT = 0b1011,
+    GT = 0b1100,
+    LE = 0b1101,
+    AL = 0b1110
+};
+
+enum class OpCode {
+    AND = 0b0000,
+    EOR = 0b0001,
+    SUB = 0b0010,
+    RSB = 0b0011,
+    ADD = 0b0100,
+    ADC = 0b0101,
+    SBC = 0b0110,
+    RSC = 0b0111,
+    TST = 0b1000,
+    TEQ = 0b1001,
+    CMP = 0b1010,
+    CMN = 0b1011,
+    ORR = 0b1100,
+    MOV = 0b1101,
+    BIC = 0b1110,
+    MVN = 0b1111
+};
+
+enum class ShiftType {
+    LSL = 0b00,
+    LSR = 0b01,
+    ASR = 0b10,
+    ROR = 0b11
+};
+
+// https://fmt.dev/dev/api.html#std-ostream-support
+std::ostream&
+operator<<(std::ostream& os, const Condition cond);
+template<>
+struct fmt::formatter<Condition> : ostream_formatter {};

include/meson.build

@@ -1,6 +1,9 @@
 headers = files(
   'memory.hh',
-  'header.hh'
+  'bus.hh',
+  'header.hh',
 )
 
+subdir('cpu')
+
 install_headers(headers, subdir: meson.project_name(), preserve_path: true)