diff --git a/applecorn.po b/applecorn.po
index ebe66db..f37f1be 100644
Binary files a/applecorn.po and b/applecorn.po differ
diff --git a/applecorn.s b/applecorn.s
index 40a8cd8..5517a88 100644
--- a/applecorn.s
+++ b/applecorn.s
@@ -72,24 +72,15 @@ AUXMOS1     EQU   $2000       ; Temp staging area in Aux
 EAUXMOS1    EQU   $3000       ; End of staging area
 AUXMOS      EQU   $D000       ; Final location in aux LC
 
-* Macro for calls from aux memory to main memory
-XFMAIN      MAC
-            CLC               ; Use main memory
-            CLV               ; Use main ZP and LC
-            JMP   XFER
-            EOM
-
 * Called by code running in main mem to invoke a
 * routine in aux memory
 XF2AUX      MAC
-            PHA
-            LDA   $C08B       ; R/W LC RAM, bank 1
-            LDA   $C08B
-            LDA   #<]1
-            STA   STRTL
-            LDA   #>]1
-            STA   STRTH
-            PLA
+            LDX   $C08B       ; R/W LC RAM, bank 1
+            LDX   $C08B
+            LDX   #<]1
+            STX   STRTL
+            LDX   #>]1
+            STX   STRTH
             SEC               ; Use aux memory
             BIT   $FF58       ; Set V: use alt ZP and LC
             JMP   XFER
@@ -98,18 +89,18 @@ XF2AUX      MAC
 * Called by code running in aux mem to invoke a
 * routine in main memory
 XF2MAIN     MAC
+            LDX   STRTL
+            STX   STRTBCKL
+            LDX   STRTH
+            STX   STRTBCKH
+            LDX   #<]1
+            STX   STRTL
+            LDX   #>]1
+            STX   STRTH
             TSX
             STX   $0101       ; Save alt SP
-            PHA
-            LDA   STRTL
-            STA   STRTBCKL
-            LDA   STRTH
-            STA   STRTBCKH
-            LDA   #<]1
-            STA   STRTL
-            LDA   #>]1
-            STA   STRTH
-            PLA
+            LDX   $0100       ; Load main SP
+            TXS
             CLC               ; Use main mem
             CLV               ; Use main ZP and LC
             JMP   XFER
@@ -117,24 +108,18 @@ XF2MAIN     MAC
 
 * Macro called on re-entry to aux memory
 ENTAUX      MAC
+            LDX   STRTBCKL
+            STX   STRTL
+            LDX   STRTBCKH
+            STX   STRTH
             LDX   $0101       ; Recover alt SP
             TXS
-            PHA
-            LDA   STRTBCKL
-            STA   STRTL
-            LDA   STRTBCKH
-            STA   STRTH
-            PLA
             EOM
 
 * Macro called on re-entry to main memory
 ENTMAIN     MAC
-            LDX   $0100       ; Recover SP
-            TXS
-            PHA               ; Preserve parm in A
-            LDA   $C081       ; Bank in ROM
-            LDA   $C081
-            PLA
+            LDX   $C081       ; Bank in ROM
+            LDX   $C081
             EOM
 
 * Enable writing to main memory (for code running in aux)
@@ -159,7 +144,6 @@ WRTAUX      MAC
             PUT   AUXMEM.VDU
             PUT   AUXMEM.HOSTFS
             PUT   AUXMEM.KERNEL
-*           PUT   AUXMEM.OSBW.ORIG
             PUT   AUXMEM.BYTWRD
             PUT   AUXMEM.CHARIO
             PUT   AUXMEM.MISC
diff --git a/auxmem.misc.s b/auxmem.misc.s
index 457f3d7..4fa94b8 100644
--- a/auxmem.misc.s
+++ b/auxmem.misc.s
@@ -145,15 +145,12 @@ PRNIB       CMP   #$0A
 * IRQ/BRK handler
 IRQBRKHDLR
             PHA
-*  >>>   WRTMAIN
-*  STA   $45      ; A->$45 for ProDOS IRQ handlers
-*  >>>   WRTAUX
 * Mustn't enable IRQs within the IRQ handler
-* Do this manually, as we have complete control at this point
+* Do not use WRTMAIN/WRTAUX macros
             STA   $C004          ; Write to main memory
             STA   $45            ; $45=A for ProDOS IRQ handlers
             STA   $C005          ; Write to aux memory
-;
+
             TXA
             PHA
             CLD
@@ -176,6 +173,7 @@ IRQBRKHDLR
 
 :IRQ        >>>   XF2MAIN,A2IRQ  ; Bounce to Apple IRQ handler
 IRQBRKRET
+            >>>   ENTAUX
             PLA                  ; TODO: Pass on to IRQ1V
             TAX
             PLA
diff --git a/loader.s b/loader.s
index c7b43a7..8f467e2 100644
--- a/loader.s
+++ b/loader.s
@@ -96,10 +96,9 @@ START       JSR   ROMMENU
             EOR   #$A5             ; Checksum
             STA   RSTV+2
 
-            TSX                    ; Save SP at $0100
-            STX   $0100            ; In main
+            TSX                    ; Save SP at $0100 in aux
             STA   $C005            ; Write to aux
-            STX   $0100            ; And also in aux
+            STX   $0100
             STA   $C004            ; Write to main
             >>>   XF2AUX,AUXMOS1