Implement INC (absolute, X).

hainesr · Oct 24, 2020 · a4c9724 · a4c9724
1 parent b296f10
commit a4c9724
Show file tree

Hide file tree

Showing 2 changed files with 26 additions and 0 deletions.
diff --git a/lib/mos6502/cpu_instructions.rb b/lib/mos6502/cpu_instructions.rb
@@ -650,6 +650,12 @@ def instructions
         # SED
         0xf8 => lambda {
           @status.decimal_mode = true
+        },
+
+        # INC (absolute, X)
+        0xfe => lambda {
+          address = absolute(@x)
+          @memory.set(address, inc(@memory.get(address)))
         }
       }
     end

diff --git a/test/cpu_instructions_test.rb b/test/cpu_instructions_test.rb
@@ -1551,4 +1551,24 @@ def test_0xf6
     assert(@cpu.zero?)
   end
 
+  def test_0xfe
+    @cpu.load!(
+      [
+        0xa9, 0xfe, 0xa2, 0x08, 0x9d, 0x92, 0x32,
+        0xfe, 0x92, 0x32, 0xfe, 0x92, 0x32
+      ]
+    )
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    assert_equal([0xfe], @cpu.dump_memory(0x329a, 1))
+    @cpu.step
+    assert_equal([0xff], @cpu.dump_memory(0x329a, 1))
+    assert(@cpu.negative?)
+    refute(@cpu.zero?)
+    @cpu.step
+    assert_equal([0x00], @cpu.dump_memory(0x329a, 1))
+    refute(@cpu.negative?)
+    assert(@cpu.zero?)
+  end
 end