On Sun, Dec 1, 2013 at 1:34 PM, nivedita datta <[email protected]>wrote:
> Hi,
>
> I an trying to implement sensor communication & have created a packet
> structure as follows:
>
> *typedef nx_struct ctr{*
> *nx_uint16_t counter;*
> *char data[20];*
> *nx_uint16_t counter2;*
> *nx_uint16_t counter3;*
> *} ctr;*
>
> *typedef nx_struct BlinkToRadioMsg {*
> * nx_uint16_t nodeid;*
> * ctr counter_;*
> *} BlinkToRadioMsg;*
>
> Say, I want to send some string from one node to other, how do I do that?
>
First, a particular given packet structure on the wire is denoted by a
given particular am_type. The simplest TinyOS network stack is
ActiveMessaging typically shorted to just AM. AM packets have a field
called the am_type (8 bits) which determines what the rest of the packet
looks like.
So in BlinkToRadioMsg, the nx_struct has a particular format and when its
gets transmitted it uses the am_type AM_BLINKTORADIO (which has the value
6).
Now that said, there hasn't really been any real coordination about who is
using what numbers for AM_TYPES, but if you change a packet format you
really should understand what you are doing.
An AM packet on a serial line looks like: (numbers in parens are the
number of bytes)
dest(2) src(2) len(1) group(1) am_type(1) <payload> <fcs>
while on a radio link (802.15.4 psuedo):
len(1) fcf(2) dsn(1) dpan(2) daddr(2) saddr(2) net(1) am_type(1)
<payload> <fcs>
In other words, if you change the packet format you should pick a different
am_type value to use.
You really should work though the TinyOS tutorials and learn a bunch more
before asking really basic questions on the email list.
more below
Please.
> Is there any way to initialize the char array other than initializing in a
> loop?
>
this is a basic C question. Please take a basic C tutorial.
there are chars (bytes), uint8_t (bytes), and strings. Strings are a
special case of chars. Then there are pointers.
if you have something like...
uint8_t * ptr;
ptr = "now is the time for all good programmers to learn C\n";
ptr points to the char array that implements the string.
Seriously go do a C tutorial.
>
> Also, does NesC packet structure support any float & string data type??
> I tried using the string datatype supported by C but it throws error
> saying:
>
C does NOT support a string data type per se.
there is no declaration like
string abc;
in C.
You are thinking C++.
nesC is a superset of C not C++.
>
> *syntax error before `string'*
>
see above.
>
>
> Please let me know how can I send float or string data type across the
> nodes.
>
Basic nesC as of 1.3.4 does not support float. However, float was added
to the msp430 code sometime around Sept 2008.
>From tos/chips/msp430/msp430hardware.h:
/* Floating-point network-type support.
> These functions must convert to/from a 32-bit big-endian integer that
> follows
> the layout of Java's java.lang.float.floatToRawIntBits method.
> Conveniently, for the MSP430 family, this is a straight byte copy...
> */
> typedef float nx_float __attribute__((nx_base_be(afloat)));
> inline float __nesc_ntoh_afloat(const void *COUNT(sizeof(float)) source)
> @safe() {
> float f;
> memcpy(&f, source, sizeof(float));
> return f;
> }
> inline float __nesc_hton_afloat(void *COUNT(sizeof(float)) target, float
> value) @safe() {
> memcpy(target, &value, sizeof(float));
> return value;
> }
> Thanks in advance for your time & effort.
>
> Regards,
> Nivedita Datta
>
> _______________________________________________
> Tinyos-help mailing list
> [email protected]
> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
>
--
Eric B. Decker
Senior (over 50 :-) Researcher
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