[U-Boot] MAC Address reading procedure in board.c

[Drasko DRASKOVIC]

Hi Wolfgang,
first of all thanks a lot for your answers.

On Mon, May 25, 2009 at 8:32 PM, Wolfgang Denk <wd at denx.de> wrote:

> Dear Drasko DRASKOVIC,
>
> In message <5ec3d7930905250856k6cffb4ber261bd99f15868c19 at mail.gmail.com>
> you wrote:
> >
> > I have been looking at MAC addr obtaining procedure in lib_arm/board.c
> and I
> > am puzzled with this implementation :
> >
> >
> > /* MAC Address */
> >     {
> >         int i;
> >         ulong reg;
> >         char *s, *e;
> >         char tmp[64];
> >
> >         i = getenv_r ("ethaddr", tmp, sizeof (tmp));
> >         s = (i > 0) ? tmp : NULL;
> >
> >         *for (reg = 0; reg < 6; ++reg) {
> >             gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s, &e, 16) :
> 0;
> >             if (s)
> >                 s = (*e) ? e + 1 : e;*
> >         }
> >     }
>
> That must be very old code. Please update to a recent version before
> trying to understand this.
>

I know that you are strongly suggesting that newes code should be used, but
sometimes it is just not my choice (although I always advocate for the newes
version).


>
> > Here are my questions:
> > 1) In which format is kept the addr in environment (i.e. why do we
> allocate
> > 64 byte buffer tmp)? This is a little bit tricky to see from the code, so
> I
> > thought maybe somebody will know.
>
> It's stored as a string "aa:bb:cc:dd:ee:ff". 64 is sufficiently large
> to catch most (acccidential) incorrect input.


Perfect! I started jumping through the tags and got lost in the see of code.
"Go to the lists...", the inner voice was telling me.


> > 2) In my opinion - there should be some delimiters (maybe ':') in this
> eth
> > addr string in environment, so we are here jumping over them :*
> >     if (s)
> >         s = (*e) ? e + 1 : e;
> > *but I still cannot see - how long are these strings between delimiters?
>
> Usually these are 2 characters long, but they can be aby size. You
> can write "0:1:2:3:4:5" or "0000:1:0002:2:04:000000005" as well, as
> long as you don't exceed the maximum of sizeof(tmp).


Aaah. Now I get it ;)


>
>
> > beyond). Why we did not took two chars to represent each of 6 bytes +
> > delimiters (':'), which would make 6*2 + 5 = 11, which should be the
> length
> > of the tmp buffer. Then take two-by-two chars and transform them into
> > number.
> > What am I missing here?
>
> Why should we make such a restriction? Why do you want to force me to
> type two characters when one may be sufficient?


You are absolutly right (I guess that was frustration of the moment talking
here).


>
> Best regards,
>
> Wolfgang Denk
>

Once again, thanks for your valuable answers. Perfect support - as always
;).

Best regards,
Drasko