[Tinyos-help] dynamic list of items in message payload

Michael Schippling schip at santafe.edu
Sun Nov 28 12:14:16 PST 2010

It's all raw bytes all the way down...
but with a good cast you can produce anything.

Create your structures however you like,
as long as they are equal to or shorter than
the maximum payload size:
     typedef nx_struct
       nx_uint8_t size;
       nx_uint16_t data1;
       nx_uint8_t data2;
     } myData;

Then create a base level TOS_Msg
(or whatever they call it these days)
and cast the data element to your struct
using a pointer:
     TOS_Msg myMessage;
     myData *myDatap;
     myDatap = (myData*) myMessage.data;

Fill in myDatap as you would with any structure pointer:
     myDatap->data1 = 0xBEEF;

Then specify the actual length when you do the Send.
Note, if you have a variable length array in your struct
you will need to calculate the actual length that you want
to send, rather than just using sizeof():
     call RStatusMsg.send( TosBaseId, sizeof(myData), myDatap);

On the Receive end you can look at your size field,
poke directly at the TOS_Msg.length, or be all
modern and data-isolated and use some abstract
interface to get the actual message length. Once
you know the length you can cast the Msgp->data
field back to your struct.

Or you could just define message types for each of
your structures as the AM gods meant you to do.

BTW can anyone explain what the "COUNT..." syntax means here?
     nx_uint8_t (COUNT(0) data)[0];
I couldn't find it in the ANSI spec I looked at...


etreu at uni-potsdam.de wrote:
> That's at least something that lead me to working solution. Ctp does  
> not uses embedded structs (neither tymo does, too). Both use 'raw'  
> bytes and point arithmetics. That's seems to be the way it works.
> Quoting wasif masood <rwmasood at gmail.com>:
>> you can get some idea form this CTP  header structure :
>> typedef nx_struct {
>>   nx_ctp_options_t    options;
>>   nx_uint16_t        parent;
>>   nx_uint16_t         etx;
>>   nx_uint8_t (COUNT(0) data)[0]; // Deputy place-holder, field will probably
>> be removed when we Deputize Ctp
>> } ctp_routing_header_t;
>> is uses flexible array.
>> On Sun, Nov 28, 2010 at 2:04 PM, <etreu at uni-potsdam.de> wrote:
>>> How can i send a varying array of items as part of a message?
>>> I cast the return of call Packet.getPayload to my struct. The struct
>>> consists of some fix attributes. One of them is the number of
>>> attributes.
>>> The last attribute is a pointer/ array of an other struct.
>>> Is there anybody who did something similar or might tell how to do this?
>>> Best regards,
>>> Enrico
>>> _______________________________________________
>>> Tinyos-help mailing list
>>> Tinyos-help at millennium.berkeley.edu
>>> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
>> --
>> Wasif Masood
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