[Discuss-gnuradio] About Latency

[KC Huang]

Hi all:

I have two questions about Gnuradio latency:

1. In transmit path, the USB delay is constant due to the 32KB buffer 
between "signal source output" and "USB". If the sampling rate is 1MS/s and 
each sample is complex 16 bits( sample size=4bytes), we can get the USB 
latency = 8ms. But how do we estimate the delay of signal processing by 
processor and USRP? I think these delays are variable depending on how 
complex the signal is and how fast the processor is. But are there any ways 
to determine what is the range of these delays?

2. fusb_options define two parameters of "fusb_nblocks" and "fusb_block_size". 
This function should be used to decrease the delay of USB. But, if we choose 
any value of number of blocks and block size, say, nblock=8 and block_size 
=2048, does that mean we need to have larger time to pass through the 8*2048 
Bytes packet than the smallest allowed 512 Bytes? So, in this logic, the 
latency of usb will increase although the throughput is increased. Am I 
correct? If not, what's wrong with my thought?

Thanks for ur reply advance!!

KC Huang