[Tinyos-host-mote-wg] Re: [Tinyos-2.0wg] OSKI TEP draft

[Philip Levis]

On Jun 20, 2005, at 4:50 PM, Joe Polastre wrote:

>> 2) A chip defines its header, footer, and metadata structures as  
>> chip-
>> specific names (e.g., CC1000Header).
>> 3) A platform maps one of its chips to the message_t. E.g., typedef
>> CC1000Header RadioHeader in a file called RadioTOSMsg.h (this lives
>> in a platform, not a chip).
>>
>
> Why does the platform do the mapping?  The chip knows which header it
> needs; why let the platform developer screw it up?  Seems like
> including the chip should take care of it.  The only reason to do it
> in the platform is the mutliple radio chips as you defined (which
> seems very wasteful)
>

Yes. Multiple chips is the reason you need to do this. What is  
wasteful about having multiple radio chips? Several existing  
platforms do...

> typedef struct TosPacket {
>   union {
>     CC1000Header cc1k_header;
>     CC2420Header cc24_header;
>     uint8_t data[TOS_MSG_LENGTH];
>     CC1000Footer cc1k_footer;
>     CC2420Footer cc24_footer;
>   }
> }
>

Er, I don't think that will work. Do you mean:

typedef struct TosPacket {
   union {
     CC1000Header cc1k;
     CC2420Header cc24;
   } header;
   uint8_t data[TOS_MSG_LENGTH];
   union {
     CC1000Footer cc1k;
     CC1000Footer cc24;
   } footer;
}

Which *really* doesn't work, as now there can be offsets between a  
packet's header and its data. Based on your comment below, I assume  
the above is what you meant?

> The problem with my proposed scheme is you can't directly read the
> buffer from the radio since it is now split across the structure.

Which you can do with the scheme I proposed....

The presence of RadioHeader and RadioFooter was merely so a chip  
could define what comes before and after the data region (before the  
metadata area) and have a global type name. But mapping those to a  
global type name is problematic due to multi-chip issues.

>
> The most memory efficient way to do this (which is the least processor
> efficient) is to do a copy or mapping to a standard struct from a
> radio struct.  sigh.
>

I don't understand. How does mapping between platform-specific and  
network structs relate to the problem of struct naming?

Phil

-------

"We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time."

- T. S. Eliot,  'Little Gidding'

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