Implement NOP (absolute, X).

hainesr · Oct 28, 2020 · 03e252b · 03e252b
1 parent 3c5e537
commit 03e252b
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diff --git a/lib/mos6502/cpu_illegal_instructions.rb b/lib/mos6502/cpu_illegal_instructions.rb
@@ -30,6 +30,11 @@ def illegal_instructions
         # NOP (implied)
         0x1a => lambda {},
 
+        # NOP (absolute, X)
+        0x1c => lambda {
+          absolute(@x)
+        },
+
         # NOP (zero page, X)
         0x34 => lambda {
           zero_page(@x)
@@ -38,6 +43,11 @@ def illegal_instructions
         # NOP (implied)
         0x3a => lambda {},
 
+        # NOP (absolute, X)
+        0x3c => lambda {
+          absolute(@x)
+        },
+
         # NOP (zero page)
         0x44 => lambda {
           zero_page
@@ -51,6 +61,11 @@ def illegal_instructions
         # NOP (implied)
         0x5a => lambda {},
 
+        # NOP (absolute, X)
+        0x5c => lambda {
+          absolute(@x)
+        },
+
         # NOP (zero page)
         0x64 => lambda {
           zero_page
@@ -64,6 +79,11 @@ def illegal_instructions
         # NOP (implied)
         0x7a => lambda {},
 
+        # NOP (absolute, X)
+        0x7c => lambda {
+          absolute(@x)
+        },
+
         # NOP (immediate)
         0x80 => lambda {
           next_byte
@@ -77,13 +97,23 @@ def illegal_instructions
         # NOP (implied)
         0xda => lambda {},
 
+        # NOP (absolute, X)
+        0xdc => lambda {
+          absolute(@x)
+        },
+
         # NOP (zero page, X)
         0xf4 => lambda {
           zero_page(@x)
         },
 
         # NOP (implied)
-        0xfa => lambda {}
+        0xfa => lambda {},
+
+        # NOP (absolute, X)
+        0xfc => lambda {
+          absolute(@x)
+        }
       }
     end
   end

diff --git a/test/cpu_illegal_instructions_test.rb b/test/cpu_illegal_instructions_test.rb
@@ -66,6 +66,26 @@ def test_0x1a_0x3a_0x5a_0x7a_0xda_0xfa
     assert_equal(0x606, @cpu.pc)
   end
 
+  # NOP (absolute, X)
+  def test_0x1c_0x3c_0x5c_0x7c_0xdc_0xfc
+    @cpu.load!(
+      [
+        0x1c, 0xa9, 0xa9, 0x3c, 0xa9, 0xa9, 0x5c, 0xa9, 0xa9,
+        0x7c, 0xa9, 0xa9, 0xdc, 0xa9, 0xa9, 0xfc, 0xa9, 0xa9
+      ]
+    )
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    assert_equal(0x00, @cpu.a)
+    assert_equal(0x00, @cpu.x)
+    assert_equal(0x00, @cpu.y)
+    assert_equal(0x612, @cpu.pc)
+  end
+
   # NOP (immediate)
   def test_0x80
     @cpu.load!([0x80, 0xff])