basicrx/lfrx: Enable frontend muxing on X3x0

The selection of frontend modes (AB, A, B, BA) is now enabled on X3x0.
Unlike older USRPs, switching the frontend is done through the antenna
API (e.g., usrp->set_rx_antenna("A")).

1 files changed, 17 insertions, 1 deletions

diff --git a/host/docs/dboards.dox b/host/docs/dboards.dox
index 0cb559061..5993501c9 100644
--- a/host/docs/dboards.dox
+++ b/host/docs/dboards.dox
@@ -11,13 +11,29 @@ of each board as well.
 
 \subsection dboards_basicrx Basic RX and LFRX
 
-The Basic RX and LFRX boards have 4 frontends:
+The Basic RX and LFRX boards have four modes of operation:
 
 -   **Frontend A:** real signal on antenna RXA
 -   **Frontend B:** real signal on antenna RXB
 -   **Frontend AB:** quadrature frontend using both antennas (IQ)
 -   **Frontend BA:** quadrature frontend using both antennas (QI)
 
+The way in which you select the mode depends on the USRP type. On the X310,
+selecting the mode is done using the antenna API:
+
+```cpp
+auto usrp = uhd::usrp::multi_usrp::make("type=x300");
+usrp->set_rx_antenna("A"); // Disable RXB port
+```
+
+On the USRP2, the N200 series, the B100 series, the E100, and the USRP1 the mode
+depends on the subdev spec applied:
+
+```cpp
+auto usrp = uhd::usrp::multi_usrp::make("type=usrp2");
+usrp->set_rx_subdev_spec("A:A"); // Disable RXB port
+```
+
 The boards have no tunable elements or programmable gains. Through the
 magic of aliasing, you can down-convert signals greater than the Nyquist
 rate of the ADC.