[Tinyos-devel] 2.0.2 CC2420

Tue Feb 12 06:07:28 PST 2008

Hi Jun,

You're correct - the strobe command only sends a single byte to the CC2420,
and the CC2420 itself automatically generates the ACK frame for the packet
you just received.

I'd certainly love to make the hardware generate a different frame because
the current ACK frame is inherently broken, but we can't change the
hardware.  The only way around this would be to generate your own ACK frame
in software and inject it into the radio's TXFIFO for transmission.  The
only reason that hasn't been done yet is A) someone needs to sit down and do
it, and B) the ack wait period will probably need to increase due to the
added delay of generating an acknowledgment in software, which may not be a
big deal.

-David

  _____  

From: Jun [mailto:yanjunrockets at gmail.com] 
Sent: Tuesday, February 12, 2008 3:24 AM
To: David Moss
Cc: tinyos-devel at millennium.berkeley.edu
Subject: Re: [Tinyos-devel] 2.0.2 CC2420

Hi, David,

I have a question on the difference between SACK and HACK. I traced the code

of SACK till CC2420SpiImpIP and found out that strobe() only sends one byte

to spi in order to generate an ACK. So does the CC2420 ratio prepare the
body 

of the ACK and sent it?  If that's true, is it possible to generate a
customized

ACK totally in HW?

Thank you,

Jun

2007/7/4 David Moss <dmm at rincon.com>:

I would be very hesitant to allow the baseline CC2420ReceiveP to perform its
former software address check to support this edge case because
acknowledgement performance may suffer as a whole, which we've already seen
and quantified to some degree.

There are a few timing issues going on with acks in the background to take
into consideration:  After the Tx mote sends its packet, the SPI bus must be
acquired by the Rx mote.  This resource acquiring may add significant delay
depending on what else is going on with the SPI bus (flash, other task
handling).  By the time the Rx mote acquires its SPI resource and is able to
download the packet, the Tx mote's ack wait period is winding down.  The Rx
mote must SACK as fast as possible to ensure the ack is received by the Tx
mote within the ack wait window.  The fastest way to SACK is to download the
first byte (length) and the second byte (fcf) to see if A) we have a valid
packet and B) if the packet requested an ack.  If we wanted to test for the
address, we'd have to download several more bytes before being able to see
the destination address.  True, it's only a few more bytes, but it's
certainly not optimized.

Another way around this case is to do what the BaseStationCC2420 does, which
is override a module from the CC2420 stack with a version that does what you
want.  I've made it fairly easy to do:  there's an FCF_LENGTH parameter in
CC2420ReceiveP which is currently set to 2 (because the FCF is 2 bytes).  By
setting it to 7, Receive will make sure the packet's length is at least 7
bytes, read those 7 bytes and SACK, then continue reading the rest of the
packet.  Because we're reading in 7 bytes from the header before SACK'ing
instead of 2, the destination address will be available and we can check it.
(attached, this file isn't tested).

If other users agree that this really isn't an edge case and we should see
this software address check version as the default, then by all means it
should be in there.  However, SACK's do not perform as well as hardware
ack's, and it's been my focus to get them optimized as much as possible.

-David

-----Original Message-----
From: Chieh-Jan (Mike) Liang [mailto:cliang4 at cs.jhu.edu]

Sent: Wednesday, July 04, 2007 11:20 AM
To: David Moss

Cc: tinyos-devel at millennium.berkeley.edu
Subject: Re: [Tinyos-devel] 2.0.2 CC2420

> ....  If you want the base
> station to disable address recognition to sniff all packets, and also send
> out SACK's when it receives a packet with its address, that's another
issue.
>
> -David
>

I think this could be useful. In addition, adding address check should
not affect the two applications you mentioned: base station and sniffer.
Any thoughts?

Thanks

Mike

> -----Original Message-----
> From: J. Ryan Stinnett [mailto:jryans at rice.edu]
> Sent: Tuesday, July 03, 2007 10:45 PM
> To: David Moss
> Cc: 'Chieh-Jan (Mike) Liang'; tinyos-devel at millennium.berkeley.edu
> Subject: Re: RE: [Tinyos-devel] 2.0.2 CC2420
>
> Does this have any effect on snooping with CC2420?  Just to confirm, the
> address recognition feature needs to be disabled as in BaseStationCC2420
> before snooping will work, is that correct?
>
> Thanks,
> Ryan
>
> David Moss wrote:
>> Yup - there's a good reason for this.  The destination address is checked
>> automatically by hardware while receiving the packet transmission.  So by
>> the time the uC gets the signal that a new packet has arrived, the packet
>> has already gone through the address/pan check.  Therefore, we don't need
> a
>> second address check in software before issuing a SACK.
>>
>> -David
>>
>>
>> -----Original Message-----
>> From: David Moss [mailto:dmm at rincon.com]
>> Sent: Tuesday, July 03, 2007 9:45 PM
>> To: 'Chieh-Jan (Mike) Liang'
>> Cc: 'tinyos-devel at Millennium.Berkeley.EDU'
>> Subject: RE: [Tinyos-devel] 2.0.2 CC2420
>>
>> Yup - there's a good reason for this.  The destination address is checked
>> automatically by hardware while receiving the packet transmission.  So by
>> the time the uC gets the signal that a new packet has arrived, the packet
>> has already gone through the address/pan check.  Therefore, we don't need
> a
>> second address check in software before issuing a SACK.
>>
>> -David
>>
>>
>>
>> -----Original Message-----
>> From: Chieh-Jan (Mike) Liang [mailto:cliang4 at cs.jhu.edu]
>> Sent: Tuesday, July 03, 2007 7:41 PM
>> To: David Moss
>> Cc: tinyos-devel at Millennium.Berkeley.EDU
>> Subject: Re: [Tinyos-devel] 2.0.2 CC2420
>>
>> Something about SACK in the new CC2420 stack is not clear to me. In the
>> old implementation, before SACK is strobed, the mote ID is compared with
>> the packet destination address. However, this check is not performed any
>> more. Is there any reason behind this?
>>
>> Thank you
>>
>> Mike
>>
>> David Moss wrote:
>>> Just updated the CC2420 stack in preparation for 2.0.2.  The file
>>> architecture has been re-arranged a little bit, making it easier to see
>>> how the stack is put together.  As a result, the .platform files that
>>> reference the cc2420 were updated.
>>>
>>>
>>>
>>> Test results are included. Let me know if you have any issues.
>>>
>>> -David
>>>
>>>
>>>
>>>
>>>
>>> Recent Updates (from the readme):
>>>
>>> * New chip SPI bus arbitration working with Receive and Transmit.
>>>
>>>
>>>
>>> * Applied TUnit automated unit testing to CC2420 development
>>>
>>>   > Caught lots of bugs, especially through regression testing
>>>
>>>   > Source code in tinyos-2.x-contribs/tunit/
>>>
>>>
>>>
>>> * Applied TEP115 behavior to CC2420 SplitControl in Csma and Lpl
>>>
>>>
>>>
>>> * Updated ActiveMessageAddressC to provide the ActiveMessageAddress
>>> interface
>>>
>>>   > Updated CC2420ConfigP to handle
>>> ActiveMessageAddress.addressChanged() and
>>>
>>>     sync automatically upon address change events.
>>>
>>>
>>>
>>> * Updated CC2420Config interface to enable/disable sw/hw
acknowledgements
>>>
>>>
>>>
>>> * Updated CC2420ConfigP to share register editing through single
> functions
>>>
>>>
>>> * Acknowledge after packet length and FCF check out valid.
>>>
>>>   > The destination address is confirmed in hardware, so we don't need
>>>
>>>     to download the entire header before acking.
>>>
>>>
>>>
>>> * Moved the getHeader() and getMetadata() commands to an internal
>> interface
>>>   called CC2420PacketBody, provided by CC2420PacketC
>>>
>>>
>>>
>>> * Separated core functionality into different sub-packages/directories
>>>
>>>   > Updated micaz, telosb, intelmote2 .platform files
>>>
>>>   > Logically organizes code
>>>
>>>
>>>
>>> * Updated some LPL architecture
>>>
>>>   > Removed continuous modulation because it didn't work 100% and I
>>> don't have
>>>
>>>     time to make it work.
>>>
>>>   > Decreased backoffs and decreased on-time for detects, saving energy.
>>>
>>>
>>>
>>> * Updated to the new AMPacket interface; made the radio set the outbound
>>>
>>>   packet's destpan after send().
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> Tinyos-devel mailing list
>>> Tinyos-devel at Millennium.Berkeley.EDU
>>>
> https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-devel
>>
>>
>

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