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Re: [Discuss-gnuradio] updated packet format on USRP inband signaling


From: David Scaperoth
Subject: Re: [Discuss-gnuradio] updated packet format on USRP inband signaling
Date: Mon, 26 Feb 2007 01:22:22 -0500

I am definitely interested in the capabilities of the in-band signaling, but my lack of experience is going to show through in this e-mail. =)

I am not sure I understand the meaning behind the 5-bit channel entry:
I thought that this might refer to channels within the total bandwidth of the incoming / outgoing signals...you said that these are "logically independent of the others" samples, and  I was thinking this was referring perhaps to frequency division of some sort (like bin values in an FFT). Could you help me understand what you mean by channels here?  

Is the control channel (0x1f), configuring the hardware(setting center frequency, registers for PGA gain...possibly an AGC in the future, etc....using the I2C & SPI...I'm actually not very familiar with SPI & I2C...)? 

Just from looking through some of the usrp host files (prims, standard, etc.) it looks like the SPI is for the devices on the motherboard, and the I2C is for the daughterboards...is this correct?   

Also, I was wondering about Timestamping...In the document you wrote

"If a packet reaches the head of the transmit queue, and the current 
time is later than the timestamp, an error is assumed to have occurred 
and the packet is discarded."

so, if the packet that is ready to be transmitted is early, then it should be discarded?  Maybe I am misunderstanding how the time stamp is going to be done.  If the timestamp (for the OUT packet) is when the data "should" go out of the D/A, then why wouldn't it just wait for the time and send .  Would that be too risky...meaning things might get backed up waiting for an incorrect time stamp that is marked two hours into the future?  Wouldn't the packets following also be "early" as well, or could that be corrected?

Thanks for any clarification that you can give,

David Scaperoth 

On Feb 25, 2007, at 6:56 PM, Eric Blossom wrote:

Would those of you with an interest in USRP inband signaling, please
take a look at the latest proposed packet format.  Now's a good time
to change things ;)

It's in trunk/usrp/doc/inband-signaling-usb


Thanks,
Eric


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