Hi Janos,
I see.
I changed the timestamping in CC2420 stack accordingly, but occasionally
wrong timestamps still pop up. My speculation is that the following corner
case is causing problem:
____ ____
__| |__| |_
As SFD pin activity shown above, a packet transmission ensues a packet
reception. The MCU does not respond to the 1st SFD rising till after the
2nd SFD rises. After the packet is read out of RXFIFO, there is no other
packet in RXFIFO and thus the timestamp of the transmitted packet is
mistakenly assigned to the received packet. I'm reading CC2420X but haven't
found how this case is dealt with. Please give me some hint. Thanks again.
-Xiaohui
On Mon, Dec 3, 2012 at 5:26 PM, Janos Sallai <[email protected]>wrote:
> The hardware is fairly deterministic: After issuing the STXON strobe the
> SFD will be transmitted with a constant delay. It's more efficient to take
> a timestamp when issuing STXON and adjust it with a constant TX_SFD_DELAY
> than servicing an SFD interrupt.
>
> Janos
>
>
> On Mon, Dec 3, 2012 at 4:10 PM, Xiaohui Liu <[email protected]> wrote:
>
>> Hi,
>>
>> Thanks for clarifying the reception timestamping.
>>
>> Why is *TX_SFD_DELAY* accounted for during transmission, but not during
>> reception? Isn't *sfdTime* the time SFD byte has been transmitted so
>> there is no need to add *TX_SFD_DELAY*?
>> * // adjust time32 with the time elapsed since the SFD event*
>> * time -= sfdTime;*
>> * time32 -= time;*
>> *
>> *
>> * // adjust for delay between the STXON strobe and the transmission of
>> the SFD*
>> * time32 += TX_SFD_DELAY;*
>> *
>> *
>> * call PacketTimeStamp.set(msg, time32);*
>>
>> -Xiaohui
>>
>> On Mon, Dec 3, 2012 at 1:45 PM, Janos Sallai
>> <[email protected]>wrote:
>>
>>> FALSE
>>
>>
>>
>>
>> --
>> -Xiaohui Liu
>> TelosB
>> TinyOS 2.1.2
>> www.cs.wayne.edu/xliu/
>>
>>
>
--
-Xiaohui Liu
TelosB
TinyOS 2.1.2
www.cs.wayne.edu/xliu/
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