Rate at which CPU gets the data

USRP ADC sampling rate = 64MSPS

Decimation Rate = x

Actual rate at which CPU gets data = 64/x MSPS

16bit for I and 16bit for Q

64/x MSPS = 64/x I samples + 64/x Q samples

So total bytes per sec = (64/x*16 + 64/x*16)/8

For x = 200

total bytes per sec =(64/200 + 64/200)*16*10^6 = 1.28 MBPS

For x = 100

total bytes per sec = 2.56 MBPS

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If the CIC starts linearly from 4 to 128, and followed by decimate by 2 Half Band Filter (HBF) Then [CIC+HBF]  should give us the following range [8,10,12,14,...........,256], and not the range [2,4,6,8,......,256] 


Reference :  http://gnuradio.4.n7.nabble.com/USRP-RX-Decimation Rate-tt11784.html

But Matt said something different

The CIC decimator does 4 through 128, but this is followed by a halfband
decimator which multiplies this by a factor of 2.  Thus, it only does
multiples of 2.  4, 6, 8, 10, 12, 14, 16, 18. 20, etc.   Up to 256 total.

Matt