Re: [PATCH 7/8] Add AT driver for STK atom.

[Denis Kenzior <denkenz@gmail.com>]

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Hi Andrew,

> Hi Denis,
> 
> On 15 April 2010 23:48, Denis Kenzior <denkenz@gmail.com> wrote:
> > The terminal response goes something like this:
> >> +
> >> +     len = sprintf(buf, "AT+CSIM=%i,A0140000%02hhX",
> >> +                     10 + length * 2, length);
> >> +
> >> +     for (; length; length--)
> >> +             len += sprintf(buf + len, "%02hhX", *value++);
> >> +
> >
> > In the new stk envelope code it goes something like this:
> >> +     len = sprintf(buf, "AT+CSIM=%i,A0C20000%02hhX",
> >> +                     12 + length * 2, length);
> >> +
> >> +     for (; length; length--)
> >> +             len += sprintf(buf + len, "%02hhX", *command++);
> >> +
> >> +     len += sprintf(buf + len, "FF");
> >
> > What is the point of this last 'FF'?  The code removed from the sim atom
> > driver doesn't have it either...
> 
> Rereading the etsi ts102.221 the "Le" field in the Envelope APDU
> (11.2.2.2) is not explictly defined "not present", instead it says
> "empty or maximum length of expected data".  It doesn't say what the
> default value is when empty so I conclude it's safer to have the field
> present or the card may think it's not allowed to send any response at
> all -- depending on the implementer's interpretation of the spec.
> 
> 10.1.6 says the field is the maximum respose length expected, but then
> some commands suggest it should be the exact length wanted and some
> make the field obligatory.

So I re-read that part of the spec, and I can see why we might want it.  
However, this quote seemed rather interesting: "Le set to '00' indicates that 
the terminal expects to receive at most the maximum number of bytes, i.e. 256, 
in the response ADPU. The UICC may return any number of bytes in the range 1 
to 256."

Shouldn't that 'FF' be changed to '00'?  Also, you might want to include the 
relevant passage or Spec/Section reference in this code so we don't wonder 
where it came from in the future.

Regards,
-Denis