Re: [Discuss-gnuradio] Bandwidth Across USB

[Lee Patton]

John -

I must have been drunk when I wrote those equations. I wrote 64e10 when
I meant 64e6, and put the D in a weird place. Sorry for any confusion.
This makes more sense:

(16 bit/sample)*(64e6/D sample/sec)*(1/2^23 MB/bit) <= 32 MB/sec

therefore, for real

D >=   16*64e6/(32*2^23) = 3.81 --> D = 4

and for complex

D >= 2*16*64e6/(32*2^23) = 7.63 --> D = 8


On Wed, 2006-04-05 at 17:46 -0400, Lee Patton wrote:
> Hi John -
> 
> 16/D bits/sample x 64e10 samples/sec x 1 B/8 bits x 1 MB / 2^20 B <= 32
> MB/sec
> 
> Therefore,
> 
> D >= 16*64e10 /(32*8*2^20) = 3.814 -> 4
> 
> So, if you want to transmit twice as many sample across the bus...
> 
> D > = 2*16*64e10 /(32*8*2^20) = 7.63 -> 8
> 
> ...you have to halve your sampling frequency.
> 
> Are you aware that there is a -8 option in some of the scripts that
> allows you to send 8 bits instead of 16.
> 
> Hope that helps,
>  - Lee
> 
> 
> 
> ----- Original Message -----
> From: jjw <address@hidden>
> Date: Wednesday, April 5, 2006 5:31 pm
> Subject: [Discuss-gnuradio] Bandwidth Across USB
> To: address@hidden
> 
> > 
> > I know this is probably an extremely stupid question, but I wanted 
> > to get
> > some verification.  I've noticed that the minimum decimation rate 
> > you can
> > use in all of the sample programs is 4 (giving you an effective 
> > samplingrate of 16 MHz).  If you are transmitting 1 real channel of 
> > data (16 bits)
> > at this rate, that seems to be maxing out the USB transfer rate of 
> > 32 MB/s. 
> > Am I correct in my deduction that you need to use a decimation rate 
> > of at
> > least 8 in order to transmit complex data (such as for FM 
> > demodulation)successfully across the USB?  Thanks. 
> > 
> > Thanks,
> > John
> > --
> > View this message in context: http://www.nabble.com/Bandwidth-
> > Across-USB-t1402318.html#a3773742
> > Sent from the GnuRadio forum at Nabble.com.
> > 
> > 
> > 
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> > 
> 
> 
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