Aviron: Fix SBIW instruction setting SREG incorrectly

sim/aviron/src/lib/Cpu.zig

@@ -755,7 +755,7 @@ const instructions = struct {
         cpu.sreg.z = (res == 0);
         cpu.sreg.n = ((res & 0x8000) != 0);
         cpu.sreg.c = ((src & 0x8000) == 0) and ((res & 0x8000) != 0);
-        cpu.sreg.v = cpu.sreg.c;
+        cpu.sreg.v = ((src & 0x8000) != 0) and ((res & 0x8000) == 0);
         cpu.sreg.s = (cpu.sreg.n != cpu.sreg.v);
     }
 

sim/aviron/src/testrunner.zig

@@ -172,8 +172,8 @@ fn run_test(
     };
 
     // Check if it was a system exit (via IO)
-    const exit_mode: ExitMode = if (io.exit_requested)
-        .{ .system_exit = io.exit_code.? }
+    const exit_mode: ExitMode = if (io.exit_code) |code|
+        .{ .system_exit = code }
     else switch (result) {
         .breakpoint => .breakpoint,
         .enter_sleep_mode => .enter_sleep_mode,
@@ -310,7 +310,6 @@ const IO = struct {
 
     // Exit status tracking
     exit_code: ?u8 = null,
-    exit_requested: bool = false,
 
     const DataBusType = aviron.Bus(.{ .address_type = u24 });
     const IOBusType = aviron.IOBus;
@@ -433,7 +432,6 @@ const IO = struct {
         switch (reg) {
             .exit => {
                 io.exit_code = value & mask;
-                io.exit_requested = true;
             },
 
             .stdio => io.stdout.append(value & mask) catch @panic("out of memory"),
@@ -497,7 +495,9 @@ const IO = struct {
 
     fn dev_check_exit(ctx: *anyopaque) ?u8 {
         const io: *IO = @ptrCast(@alignCast(ctx));
-        if (io.exit_requested) return io.exit_code;
+        if (io.exit_code) |code| {
+            return code;
+        }
         return null;
     }
 };

sim/aviron/testsuite.avr-gcc/instructions/sbiw.S

@@ -0,0 +1,56 @@
+//! {
+//!   "exit": "breakpoint",
+//!   "cpus": ["atmega2560", "atmega328p"],
+//!   "precondition": {
+//!     "r24": 0,
+//!     "r25": 0,
+//!     "r26": 0,
+//!     "r27": 128,
+//!     "r28": 8,
+//!     "r29": 0,
+//!     "r30": 255,
+//!     "r31": 255 },
+//!   "postcondition": {
+//!     "r16": 21,
+//!     "r17": 24,
+//!     "r18": 2,
+//!     "r19": 20,
+//!     "r24": 248,
+//!     "r25": 255,
+//!     "r26": 255,
+//!     "r27": 127,
+//!     "r28": 0,
+//!     "r29": 0,
+//!     "r30": 192,
+//!     "r31": 255 }
+//! }
+
+    ; Test case 1: 0x0000 - 0x08 = 0xFFF8
+    ; Precondition: r25:r24 = 0x0000
+    ; Expected: r25:r24 = 0xFFF8, C=1, N=1, V=0, S=1, Z=0
+    ; SREG should be 0x15 (C=1, Z=0, N=1, V=0, S=1)
+    sbiw r24, 0x8
+    in r16, 0x3F    ; Save SREG to r16
+
+    ; Test case 2: 0x8000 - 0x01 = 0x7FFF (overflow)
+    ; Precondition: r27:r26 = 0x8000
+    ; Expected: r27:r26 = 0x7FFF, C=0, N=0, V=1, S=1, Z=0
+    ; SREG should be 0x18 (C=0, Z=0, N=0, V=1, S=1)
+    sbiw r26, 0x1
+    in r17, 0x3F    ; Save SREG to r17
+
+    ; Test case 3: 0x0008 - 0x08 = 0x0000 (zero result)
+    ; Precondition: r29:r28 = 0x0008
+    ; Expected: r29:r28 = 0x0000, C=0, N=0, V=0, S=0, Z=1
+    ; SREG should be 0x02 (C=0, Z=1, N=0, V=0, S=0)
+    sbiw r28, 0x8
+    in r18, 0x3F    ; Save SREG to r18
+
+    ; Test case 4: 0xFFFF - 0x3F = 0xFFC0
+    ; Precondition: r31:r30 = 0xFFFF
+    ; Expected: r31:r30 = 0xFFC0, C=0, N=1, V=0, S=1, Z=0
+    ; SREG should be 0x14 (C=0, Z=0, N=1, V=0, S=1)
+    sbiw r30, 0x3F
+    in r19, 0x3F    ; Save SREG to r19
+
+    break