output std usrp tx & rx

root@azure-stk:/usr/local/src/gnuradio-3.3.0/usrp/host/apps# ./test_usrp_standard_tx
which:    0
interp:   16
rf_freq:  -1
amp:      10000.000000
nsamples: 3.2e+07
Subdevice name is Flex 900 Tx
Subdevice freq range: (7.5e+08, 1.05e+09)
mux: 0x000098
baseband rate: 8e+06
target_freq:     900000000.000000
ok:              true
r.baseband_freq: 904000000.000000
r.dxc_freq:      -4000000.000000
r.residual_freq: 0.000000
r.inverted:      0
xfered 3.2e+07 bytes in 1 seconds.  3.199e+07 bytes/sec.  cpu time = 0.12
0 underruns

root@azure-stk:/usr/local/src/gnuradio-3.3.0/usrp/host/apps# ./test_usrp_standard_rx
xfered 1.34e+08 bytes in 4.19 seconds.  3.2e+07 bytes/sec.  cpu time = 0.56
noverruns = 0