Update radio/USRP/README.md

radio/USRP/README.md

@@ -4,33 +4,46 @@ OAI works with the most common USRP models like, B200, B200mini, B210, X310, N30
 
 The USRP can be configured in the RU section of the config file. The field "sdr_addrs" uses the same syntax as the USRP device identification string (https://files.ettus.com/manual/page_identification.html). Here are a few examples
 
+```bash
 sdr_addrs = "addr=192.168.10.2" # uses a single 10Gb Ethernet interface on an N3x0 or X3x0 or X4x0
 
+
 sdr_addrs = "addr=192.168.10.2,second_addr=192.168.20.2" # uses 2 10Gb Ethernet interfaces on a N3x0 or X3x0 or X4x0 (requires that you flashed the FPGA wth the XG image)
+```
 
 you can also use the multi USRP feature and specify multiple USRPs, in which case you will get the aggregated number of channels on all the devices
 
+```bash
 sdr_addrs = "addr0=192.168.10.2,addr1=192.168.30.2"
+```
 
 You can specify if you want to use external or interal clock or time source either by adding the parameters in the sdr_addrs field or by using the fields clock_src or time_src
 
+```bash
 sdr_addrs = "addr=192.168.10.2,clock_source=external,time_source=external"
+```
 
 is equivalent to
 
+```bash
 sdr_addrs = "addr=192.168.10.2"
 clock_src = "external"
 time_src  = "external"
+```
+
+Valid choices for clock and time source are "internal", "external", and "gpsdo".
 
-Valid choices for clock and time source are "internal", "external", and "gpsdo"
+Note 1: the USRP remembers the choice of the clock source. If you want to make sure it uses always the same, always specify the clock_source and time_source.
 
-Careful: the USRP remembers the choice of the clock source. If you want to make sure it uses always the same, always specify the clock_source and time_source.
+Note 2: when using multiple USRPs they always have to be synchronized using "external" or "gpsdo"
 
 Last but not least you may specify that only a specfic subdevice of the USRP is used. See also https://files.ettus.com/manual/page_configuration.html#config_subdev
 
 For example on a USRP N310 the following fields will specify that you use channel 0 of subdevice A.
 
+```bash
 tx_subdev = "A:0"
 rx_subdev = "A:0"
+```
 
-When combining this with the multi USRP feature you can easily create a distributed antenna array with only 1 channel used at each USRP.
\ No newline at end of file
+When combining this with the multi USRP feature you can easily create a distributed antenna array with only 1 channel used at each USRP.