diff --git a/kernel/kernelvec.S b/kernel/kernelvec.S
index 5fce79a..3e9d3e9 100644
--- a/kernel/kernelvec.S
+++ b/kernel/kernelvec.S
@@ -101,9 +101,10 @@ timervec:
         sd a2, 8(a0)
         sd a3, 16(a0)
 
-        # add another second to mtimecmp0.
+        # schedule the next timer interrupt
+        # by adding interval to mtimecmp.
         ld a1, 32(a0) # CLINT_MTIMECMP(hart)
-        ld a2, 40(a0) # ticks per second
+        ld a2, 40(a0) # interval
         ld a3, 0(a1)
         add a3, a3, a2
         sd a3, 0(a1)
diff --git a/kernel/trap.c b/kernel/trap.c
index 6d5e46b..53d86ca 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -191,7 +191,7 @@ devintr()
 
     plic_complete(irq);
     return 1;
-  } else if(scause == 0x8000000000000001){
+  } else if(scause == 0x8000000000000001L){
     // software interrupt from a machine-mode timer interrupt,
     // forwarded by timervec in kernelvec.S.