Merge pull request #7 from gapry/op_ret

Decode RET Opcode
gapry · Jun 3, 2024 · d0c974c · d0c974c
2 parents 7f4d27b + 0ad423a
commit d0c974c
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Showing 3 changed files with 34 additions and 3 deletions.
diff --git a/arabica/cpu/cpu.cpp b/arabica/cpu/cpu.cpp
@@ -4,8 +4,20 @@
 namespace arabica {
 
 void CPU::run(const Memory& memory) {
-  instruction = memory[pc] << 8 | memory[pc + 1];
-  opcode      = static_cast<OP_CODE>(instruction & 0xF000);
+  instruction     = memory[pc] << 8 | memory[pc + 1];
+  uint16_t prefix = instruction & 0xF000;
+  uint16_t suffix = instruction & 0x00FF;
+  opcode          = static_cast<OP_CODE>(prefix);
+
+  switch (prefix) {
+    case 0x0: {
+      switch (suffix) {
+        case 0xEE: opcode = OP_CODE::RET; break;
+        default:; break;
+      }
+    } break;
+    default: break;
+  }
 
   switch (opcode) {
     case OP_CODE::JP_addr: {
@@ -17,6 +29,14 @@ void CPU::run(const Memory& memory) {
       uint16_t target = instruction & 0x0FFF;
       pc              = target;
     } break;
+    case OP_CODE::RET: {
+      if (!stack.empty()) {
+        pc = stack.top();
+        stack.pop();
+      } else {
+        // ToDo: raise interrupt? how to test the failed case?
+      };
+    } break;
     default: {
       fmt::print("Unknown opcode: 0x{:X}\n", static_cast<uint16_t>(opcode));
     } break;

diff --git a/arabica/cpu/cpu.hpp b/arabica/cpu/cpu.hpp
@@ -27,7 +27,6 @@ class CPU : public noncopyable {
   uint8_t              reg_delay{DEFAULT_RATE_HZ};
   uint8_t              reg_sound{DEFAULT_RATE_HZ};
   uint16_t             pc{PC_START};
-  uint8_t              sp{0x00};
   std::stack<uint16_t> stack;
   uint16_t             instruction{0x0000};
   OP_CODE              opcode{OP_CODE::CLS};

diff --git a/test/cpu/cpu_test_suite.hpp b/test/cpu/cpu_test_suite.hpp
@@ -27,3 +27,15 @@ arabica_cpu_test(test_call,
   ASSERT_EQ(cpu.stack.size(), 1);
   ASSERT_EQ(cpu.stack.top(), 0x202);
 )
+
+arabica_cpu_test(test_ret, 
+  memory.write(0x200, 0x26);
+  memory.write(0x201, 0x00);
+  cpu.run(memory);
+
+  memory.write(0x600, 0x00);
+  memory.write(0x601, 0xEE);
+  cpu.run(memory);
+  ASSERT_EQ(cpu.pc, 0x202);
+  ASSERT_EQ(cpu.stack.size(), 0);
+)