USRP Problems with decim_rate = 4

I think the USRP can provide the minimum decimate rate of 4. So I
changed the output data format from short to char. With 8-bit I & Q
decim = 4 ->64M/4= 16MS/sec ,I&Q -> 32MB/sec. That is within the range
of my USB speed. In the make_format() function I set the width = 8,
shift = 8. Then the out put of USRP will be char data. But when I read
the data from the USRP, I found all of them are just 0s. When I change
the decim_rate = 8, then I can get the right results. So I want to know
what is wrong in my method? How can I get data with decim_rate = 4?


You can use USRP with decim_rate = 4 only if you use FPGA image
std_4rx_0tx.rbf (no half band filter). See: