diff --git a/avr/devices/all/hw_m644p.asm b/avr/devices/all/hw_m644p.asm
index ccb7f71..f681530 100644
--- a/avr/devices/all/hw_m644p.asm
+++ b/avr/devices/all/hw_m644p.asm
@@ -103,13 +103,11 @@ systemSetupTimer0:            ; setup timer for IRQ every 100ms
   ldi r16, 1
   sts baseTimerModuleReloadValue, r16
   sts baseTimerModuleTickCounter, r16
-.endif
 
-;
 ; Settings for clock 8Mhz
 ; use timer0 with OCR0=78 (irq every 9.984 millisecs), baseTimerModuleReloadValue 10
 ;
-.if clock == 8000000
+.elif clock == 8000000
   ; CMP interrupt about every 10ms
   ldi r16, 78-1
   outr OCR0A, r16
@@ -117,6 +115,24 @@ systemSetupTimer0:            ; setup timer for IRQ every 100ms
   ldi r16, 10
   sts baseTimerModuleReloadValue, r16
   sts baseTimerModuleTickCounter, r16
+.elif clock == 10000000
+  ; CMP-A interrupt about every 10ms
+  ldi r16, 98-1      ; (10,000,000/1024)/10 = 97.65625
+  outr OCR0A, r16
+
+  ldi r16, 10
+  sts baseTimerModuleReloadValue, r16
+  sts baseTimerModuleTickCounter, r16
+.elif clock == 20000000
+  ; CMP-A interrupt about every 5ms
+  ldi r16, 98-1
+  outr OCR0A, r16
+
+  ldi r16, 20
+  sts baseTimerModuleReloadValue, r16
+  sts baseTimerModuleTickCounter, r16
+.else
+  .error "Unhandled clock frequency"
 .endif
 
   ldi r16, (1<<OCF0A)         ; clear pending interrupts