[Tinyos-devel] Crc interface buffer size restriction

[Philip Levis]

On Jan 14, 2009, at 1:07 AM, Andreas Köpke wrote:

>
> Vlado Handziski wrote:
>> On Tue, Jan 13, 2009 at 11:07 PM, Philip Levis  
>> <pal at cs.stanford.edu> wrote:
>>> On Jan 13, 2009, at 1:41 PM, Philip Levis wrote:
>>>
>>> One other thought: if you want a 16-bit length CRC interface,  
>>> chances
>>> are you want it to be split-phase, due to the possible time duration
>>> of the operation.
>>
>> There are also alternative table look up versions in the eyesIFX  
>> folder
>> that can be useful.
>>
>
> However, the table lookup is only twice as fast as the current default
> implementation, which itself is an 10 times improvement over the  
> original bit
> shift for loop. You might want to do time measurements before  
> deciding whether
> it should be split phase: the LPL channel check for telosb takes  
> 11ms in an
> atomic block

This is totally broken and should be fixed.


> and the 64bit multiplication of the default random number
> generator takes about 1ms in an atomic block.

It's doing the multiplication in software because the codegen for  
multiply is broken in the gcc version we use. IIRC, boomerang solved  
this by doing a little bit of assembly for a hw multiply. We might  
want to do the same thing.


> So I guess we can spare the 1ms
> for 16bit CRC in an non-atomic block easily.

My concern was doing a CRC over 65,535 bytes. That would take much  
more than 1ms, right?

Phil