fix(rp2040): SUBS alignment to CMP implementation

close #56
wokwi · May 31, 2021 · 50a3496 · 50a3496
1 parent 33e6467
commit 50a3496
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Showing 2 changed files with 33 additions and 3 deletions.
diff --git a/src/instructions.spec.ts b/src/instructions.spec.ts
@@ -1325,6 +1325,34 @@ describe('Cortex-M0+ Instruction Set', () => {
     expect(registers.V).toEqual(false);
   });
 
+  it('should execute a `subs r5, r3, r2` instruction and set N V flags', async () => {
+    await cpu.setPC(0x20000000);
+    await cpu.writeUint16(0x20000000, opcodeSUBSreg(r5, r3, r2));
+    await cpu.setRegisters({ r3: 0 });
+    await cpu.setRegisters({ r2: 0x80000000 });
+    await cpu.singleStep();
+    const registers = await cpu.readRegisters();
+    expect(registers.r5).toEqual(0x80000000);
+    expect(registers.N).toEqual(true);
+    expect(registers.Z).toEqual(false);
+    expect(registers.C).toEqual(false);
+    expect(registers.V).toEqual(true);
+  });
+
+  it('should execute a `subs r5, r3, r2` instruction  and set Z C flags', async () => {
+    await cpu.setPC(0x20000000);
+    await cpu.writeUint16(0x20000000, opcodeSUBSreg(r5, r3, r2));
+    await cpu.setRegisters({ r2: 0x80000000 });
+    await cpu.setRegisters({ r3: 0x80000000 });
+    await cpu.singleStep();
+    const registers = await cpu.readRegisters();
+    expect(registers.r5).toEqual(0);
+    expect(registers.N).toEqual(false);
+    expect(registers.Z).toEqual(true);
+    expect(registers.C).toEqual(true);
+    expect(registers.V).toEqual(false);
+  });
+
   it('should raise an SVCALL exception when `svc` instruction runs', async () => {
     const SVCALL_HANDLER = 0x20002000;
     await cpu.setRegisters({ sp: 0x20004000 });

diff --git a/src/rp2040.ts b/src/rp2040.ts
@@ -1633,12 +1633,14 @@ export class RP2040 {
       const Rd = opcode & 0x7;
       const leftValue = this.registers[Rn];
       const rightValue = this.registers[Rm];
-      const result = (leftValue - rightValue) | 0;
+      const result = leftValue - rightValue;
       this.registers[Rd] = result;
-      this.N = (leftValue | 0) < (rightValue | 0);
+      this.N = !!(result & 0x80000000);
       this.Z = leftValue === rightValue;
       this.C = leftValue >= rightValue;
-      this.V = (leftValue | 0) < 0 && rightValue > 0 && result > 0;
+      this.V =
+        (!!(result & 0x80000000) && !(leftValue & 0x80000000) && !!(rightValue & 0x80000000)) ||
+        (!(result & 0x80000000) && !!(leftValue & 0x80000000) && !(rightValue & 0x80000000));
     }
     // SVC
     else if (opcode >> 8 === 0b11011111) {