AVR-Chat

--- In AVR-Chat@yahoogroups.com, "leon_heller" <leon.heller@d...> 
wrote:
> I've just written a simple jump table program using ICALL:

Your jump table would be better if it consisted only of addresses as 
opposed to the call/return.  That saves both time and space.  I use 
the GNU assembler (comes with gcc) but the idea is the same.  You'll 
just have to convert to the Atmel way of doing things.

Also, unless you can guarantee that the table doesn't cross a 256-byte 
boundary you need to propagate the carry to the high byte.

Depending on what registers you have available, this code can be made 
shorter and more efficient.  This is written using gcc register 
conventions.  In particular, r0 is a temporary register and r1 is 
always zero.  This code also assumes that the index value (in r24) is 
never more than 127.

  ldi  r30, lo8(jmpTable)
  ldi  r31, hi8(jmpTable)
  add  r24, r24
  add  r30, r24
  adc  r31, r1
  ld   r0, Z+
  ld   r31, Z
  mov  r30, r0
  icall

; this table contains the program memory addresses of the specified 
labels
jmpTable:
  .word	pm(one)
  .word pm(two)
  .word pm(three)
  ...
  .word pm(eight)