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

[Wolfgang Denk]

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.

> 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.

> 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).

> 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?

Best regards,

Wolfgang Denk

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