Implement the last set of ops. RETs

2 files changed, 29 insertions, 0 deletions

diff --git a/src/main/kotlin/cpu/Cpu.kt b/src/main/kotlin/cpu/Cpu.kt
index 32fd39a..91150c4 100644
--- a/src/main/kotlin/cpu/Cpu.kt
+++ b/src/main/kotlin/cpu/Cpu.kt
@@ -21,6 +21,7 @@ class Cpu {
     stdCommandGroup.putAll(jumps)
     stdCommandGroup.putAll(calls)
     stdCommandGroup.putAll(restarts)
+    stdCommandGroup.putAll(returns)
     standardOpcodes = stdCommandGroup.toMap()
 
     val extCommandGroup: MutableMap<Int, Operation> = mutableMapOf()
diff --git a/src/main/kotlin/cpu/opcodes/Returns.kt b/src/main/kotlin/cpu/opcodes/Returns.kt
new file mode 100644
index 0000000..b78e2d6
--- /dev/null
+++ b/src/main/kotlin/cpu/opcodes/Returns.kt
@@ -0,0 +1,28 @@
+package cpu.opcodes
+
+import cpu.Operation
+import cpu.Registers
+import ram.Ram
+import BitManipulation as bm
+
+val returns = mapOf(
+
+  0xC9 to Operation("RET", 0, 8, {r, m, _ -> ret(r, m)}),
+
+  0xC0 to Operation("RET NZ,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.ZERO) == 0) ret(r, m)}),
+  0xC8 to Operation("RET Z,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.ZERO) == 1) ret(r, m)}),
+  0xD0 to Operation("RET NC,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.CARRY) == 0) ret(r, m)}),
+  0xD8 to Operation("RET C,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.CARRY) == 1) ret(r, m)}),
+
+  // TODO - enable interrupts once added
+  0xC9 to Operation("RET", 0, 8, {r, m, _ -> ret(r, m)})
+
+)
+
+private fun ret(r: Registers, m: Ram) {
+
+  val lsb = m.readByte(r.getAndIncrementSP())
+  val msb = m.readByte(r.getAndIncrementSP())
+
+  r.PC = bm.bytesToWord(msb, lsb)
+}
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