feat: implement STX

2 files changed, 29 insertions, 4 deletions

diff --git a/src/instruction.spec.ts b/src/instruction.spec.ts
index 9ea4c0f..8c81a06 100644
--- a/src/instruction.spec.ts
+++ b/src/instruction.spec.ts
@@ -46,10 +46,21 @@ describe('avrInstruction', () => {
     expect(cpu.cycles).toEqual(2);
   });
 
+  it('should execute `ST X, r1` instruction', () => {
+    loadProgram('1c92');
+    cpu.data[1] = 0x5a; // r1 <- 0x5a
+    cpu.data[26] = 0x9a; // X <- 0x9a
+    avrInstruction(cpu);
+    expect(cpu.pc).toEqual(1);
+    expect(cpu.cycles).toEqual(1);
+    expect(cpu.data[0x9a]).toEqual(0x5a);
+    expect(cpu.data[26]).toEqual(0x9a); // verify that X was unchanged
+  });
+
   it('should execute `ST X+, r1` instruction', () => {
     loadProgram('1d92');
-    cpu.data[1] = 0x5a; // put the value 5a in r1
-    cpu.data[26] = 0x9a; // X <- 0x19
+    cpu.data[1] = 0x5a; // r1 <- 5a
+    cpu.data[26] = 0x9a; // X <- 0x9a
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
@@ -57,6 +68,17 @@ describe('avrInstruction', () => {
     expect(cpu.data[26]).toEqual(0x9b); // verify that X was incremented
   });
 
+  it('should execute `ST X-, r17` instruction', () => {
+    loadProgram('1e93');
+    cpu.data[17] = 0x88; // r17 <- 0x88
+    cpu.data[26] = 0x99; // X <- 0x99
+    avrInstruction(cpu);
+    expect(cpu.pc).toEqual(1);
+    expect(cpu.cycles).toEqual(2);
+    expect(cpu.data[0x98]).toEqual(0x88);
+    expect(cpu.data[26]).toEqual(0x98); // verify that X was unchanged
+  });
+
   it('should execute `CPI r26, 0x9` instruction', () => {
     loadProgram('a930');
     cpu.data[26] = 0x8;
diff --git a/src/instruction.ts b/src/instruction.ts
index f7789d2..63c4caa 100644
--- a/src/instruction.ts
+++ b/src/instruction.ts
@@ -425,7 +425,7 @@ export function avrInstruction(cpu: ICPU) {
 
   /* STX */
   if ((opcode & 0xfe0f) === 0x920c) {
-    /* not implemented */
+    cpu.writeData(cpu.dataView.getUint16(26, true), cpu.data[(opcode & 0x1f0) >> 4]);
   }
 
   /* STX */
@@ -436,7 +436,10 @@ export function avrInstruction(cpu: ICPU) {
 
   /* STX */
   if ((opcode & 0xfe0f) === 0x920e) {
-    /* not implemented */
+    const i = cpu.data[(opcode & 0x1f0) >> 4];
+    cpu.dataView.setUint16(26, cpu.dataView.getUint16(26, true) - 1, true);
+    cpu.writeData(cpu.dataView.getUint16(26, true), i);
+    cpu.cycles++;
   }
 
   /* STY */