diff --git a/common.h b/common.h
index 27c5d3f..6d935cc 100644
--- a/common.h
+++ b/common.h
@@ -374,29 +374,38 @@ idt_descriptor:
 .macro ISR_NOERRCODE i
     isr\()\i:
         cli
+        /*
+        Push a dummy 0 for interrupts that don't push any code.
+        http://stackoverflow.com/questions/10581224/why-does-iret-from-a-page-fault-handler-generate-interrupt-13-general-protectio/33398064#33398064
+        */
         push $0
         push $\i
-        jmp interrupt_handler
+        jmp interrupt_handler_stub
 .endm
 
 .macro ISR_ERRCODE i
     isr\()\i:
         cli
         push $\i
-        jmp interrupt_handler
+        jmp interrupt_handler_stub
 .endm
 
 /*
 Entries and handlers.
 48 = 32 processor built-ins + 16 PIC interrupts.
+In addition to including this, you should also call
+- call IDT_SETUP_48_ISRS to setup the handler addreses.
+- define an `interrupt_handler(uint32 number, uint32 error)` function
 */
 .macro IDT_48_ENTRIES
+    /* IDT. */
     IDT_START
     .rept 48
     IDT_ENTRY
     .endr
     IDT_END
 
+    /* ISRs */
     .irp i, 0, 1, 2, 3, 4, 5, 6, 7
         ISR_NOERRCODE \i
     .endr
@@ -411,6 +420,19 @@ Entries and handlers.
             40, 41, 42, 43, 44, 45, 46, 47, 48
         ISR_NOERRCODE \i
     .endr
+
+    /* Factor out things which we will want to do in every handler. */
+    interrupt_handler_stub:
+        cli
+        call interrupt_handler
+        /* If we are a PIC interrupt (>=32), do an EOI. */
+        cmp $0x20, (%esp)
+        jb interrupt_handler_stub.noeoi
+        PIC_EOI
+    interrupt_handler_stub.noeoi:
+        add $8, %esp
+        sti
+        iret
 .endm
 
 .macro IDT_SETUP_48_ISRS
@@ -614,11 +636,11 @@ Expected output on screen:
 
     12345678
 */
-.macro VGA_PRINT_HEX_4 reg=<%eax>
+.macro VGA_PRINT_HEX_4 in=<%eax>
     LOCAL loop
     PUSH_EADX
     /* Null terminator. */
-    mov \reg, %ecx
+    mov \in, %ecx
 
     /* Write ASCII representation to memory. */
     push $0
@@ -739,6 +761,18 @@ but you don't have to wait much for each one.
     out %al, PORT_PIT_CHANNEL0
 .endm
 
+/*
+Define the properties of the wave:
+
+- Channel: 0
+- access mode: lobyte/hibyte
+- operating mode: rate generator
+- BCD/binary: binary
+*/
+.macro PIT_GENERATE_FREQUENCY
+    OUTB $0b00110100, PORT_PIT_MODE
+.endm
+
 /* IVT */
 
 #define IVT_PIT 8
diff --git a/pit.S b/pit.S
index c98d7d7..f13f732 100644
--- a/pit.S
+++ b/pit.S
@@ -65,15 +65,7 @@ TODO learn to turn off the PIT after some iterations
 BEGIN
     IVT_PIT_SETUP
 
-    /*
-    Define the properties of the wave:
-
-    - Channel: 0
-    - access mode: lobyte/hibyte
-    - operating mode: rate generator
-    - BCD/binary: binary
-    */
-    OUTB $0b00110100, PORT_PIT_MODE
+    PIT_GENERATE_FREQUENCY
 
     /*
     Set frequency of Channel 0.
diff --git a/pit_protected.S b/pit_protected.S
index 367573d..51cf540 100644
--- a/pit_protected.S
+++ b/pit_protected.S
@@ -9,16 +9,12 @@ BEGIN
     PROTECTED_MODE
     IDT_SETUP_48_ISRS
     REMAP_PIC_32
-    OUTB $0b00110100, PORT_PIT_MODE
+    PIT_GENERATE_FREQUENCY
     PIT_SET_MIN_FREQ
     sti
     jmp .
 IDT_48_ENTRIES
 interrupt_handler:
-    pop %eax
+    mov 4(%esp), %eax
     VGA_PRINT_HEX_4 <%eax>
-    OUTB $0x61, $0x20
-    PIC_EOI
-    add $4, %esp
-    sti
-    iret
+    ret