AVR-Chat

--- Dave VanHorn <dvanhorn@dvanhorn.org> wrote:
> 
> 
> For speed, I need to have a bunch of operations that
> I would normally loop, 
> set up in straightline code.
> I also need to control how many of these operations
> that I execute, by 
> varying the entry point.
> 
> I seem to remember a way to implement vectored
> jumps, but I can't think 
> what it was offhand.
> 
> Each entry might be 6-10 instructions, and there may
> be 256 of them, so 
> whatever it is, needs to not use rjmps.
> Definitely trading codespace for speed here!, and
> one of the few places 
> where I'm likely to use a macro.
> 
hi;

I has same problem before,
the best way I found is this:

ensure this table is aligned on 128 word boundry:
jump_tbl:
        rjmp  loc_00
        rjmp  loc_01
        ....
        rjmp  loc_FF ;entry 255
jump_it: //pass function index in ZL
        ldi ZH,hi8(jump_tbl*2)
        ijmp

so the overhead is about 6 cycles only.

good lock.
commonly the best way is the simplest way.


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com