Built device interrupts

src/tests.zig

@@ -36,6 +36,8 @@ fn check(name: []const u8, ok: bool) void {
 pub fn run(case: []const u8, boot_info: *const BootInfo) void {
     if (eql(case, "smoke")) {
         smoke(boot_info);
+    } else if (eql(case, "timer")) {
+        timer();
     } else if (eql(case, "fault-ud")) {
         faultInvalidOpcode();
     } else if (eql(case, "fault-pf")) {
@@ -91,6 +93,26 @@ fn smoke(boot_info: *const BootInfo) void {
     log("DANOS-TEST-DONE\n", .{});
 }
 
+/// Verify device interrupts fire and return: the timer tick counter must advance
+/// on its own. Interrupts are already enabled by kmain before tests run.
+fn timer() void {
+    log("DANOS-TEST-BEGIN: timer\n", .{});
+    const start = arch.ticks();
+    // Busy-wait for the counter to advance. arch.ticks() is a volatile load, so
+    // the compiler re-reads it each iteration and sees the interrupt's update.
+    // The cap is only a safety net; the harness timeout is the real backstop.
+    var spins: u64 = 0;
+    while (arch.ticks() == start and spins < 5_000_000_000) spins +%= 1;
+    check("timer interrupts advance the tick count", arch.ticks() > start);
+
+    log("DANOS-TEST-RESULT: {s} ({d} passed, {d} failed)\n", .{
+        if (failed == 0) "PASS" else "FAIL",
+        passed,
+        failed,
+    });
+    log("DANOS-TEST-DONE\n", .{});
+}
+
 fn faultInvalidOpcode() void {
     log("DANOS-TEST-BEGIN: fault-ud\n", .{});
     asm volatile ("ud2");
@@ -108,6 +130,7 @@ fn faultPageFault() void {
 
 fn faultDoubleFault() void {
     log("DANOS-TEST-BEGIN: fault-df\n", .{});
+    arch.disableInterrupts(); // so only the ud2 delivery (not a timer tick) triggers the #DF
     // Point RSP at unmapped memory, then fault: the CPU can't push the fault
     // frame, which escalates to #DF — survivable only because #DF runs on IST1.
     var bad_sp: u64 = 0x5000000000;