Can this faster / with less ROM

Christophe · Joined: 10 May 2005 Posts: 323 Location: Belgium

Hello,

I read that printf instructions use a lot of ROM.
I use a lot of these:

Ttelmah · Guest

Are the bytes constants or variables?.
There should not be a lot in it for a late compiler (the optimiser is fairly 'smart' for this type of simple operation). Where printf, drinks memory, is first, if you do 'simple' numeric outputs, which themselves will involve a lot of divisions etc., and even worse, when you start dealing with float values.The problem is that an understanding of just how much actual 'work' is involved in a tiny statement, like:
printf("%5.2f/n",val);
is often lacking...
Looking at your example, simply changing to:

Christophe · Joined: 10 May 2005 Posts: 323 Location: Belgium

constants

Christophe · Joined: 10 May 2005 Posts: 323 Location: Belgium

Ttelmah · Guest

Yes, you cannot send a trailing '0' this way (the only character you can't), since it is seen as the 'end' of the printf string. The other constants can be, but I doubt if you will save anything. The compiler is bright enough to know that with constants, it just has to load the value, and send it.
If you only have to send a couple of constant values, you are not going to save anything. If the list is a lot longer, there are other tricks that can help (the overhead of fetching a list from ROM, is probably equivalent to about five values - above this length, this will be better, but below this length it'll be worse, so using this technique only becomes worthwhile for longer messages).

Best Wishes

libor · Joined: 14 Dec 2004 Posts: 288 Location: Hungary

Cristophe, I see all your commandos are four-letter words (no pun intended :-) , so you can perhaps organize them into a lookup table, and make a custom printf routine, that would take only an index into this table as a parameter.

Christophe · Joined: 10 May 2005 Posts: 323 Location: Belgium

libor,

could you make a small example? I don't understand what you mean.

thx for the input all