[Discuss-gnuradio] mux on usrp Tx side

[Achilleas Anastasopoulos]

I understand the purpose of the mux on the rx side of the usrp.

I have a question regarding the tx side of the usrp.
In particular, it is not clear to me what the purpose of the mux
is on the tx side.
My understanding is that the samples from the USB (say complex)
are interpolated by N in the FPGA, then further interpolated
by 4 in the DAC chip (to reach 128Msps), then digitally up-converted and 
then digital-to-analog converted.

where is the Mux in this chain? and what does the default value 152 
represent?

Thanks
Achilleas