docs: Added some info on X3x0 dboard_clock_rate and which dboards need to set it.

2 files changed, 43 insertions, 0 deletions

diff --git a/host/docs/dboards.dox b/host/docs/dboards.dox
index 2ce6c4563..4f2b22825 100644
--- a/host/docs/dboards.dox
+++ b/host/docs/dboards.dox
@@ -101,6 +101,9 @@ Sensors:
 
 -   **lo_locked**: boolean for LO lock state
 
+Notes:
+- When used in the X3x0, set the daughterboard clock rate to 100 MHz (see \ref config_devaddr)
+
 \subsection dboards_rfx RFX Series
 
 The RFX Series boards have 2 quadrature frontends: Transmit and Receive.
@@ -343,6 +346,12 @@ LEDs:
 -   **TX/RX RXD**: Receiving on TX/RX antenna port
 -   **RX2 RXD**: Receiving on RX2 antenna port
 
+
+Notes:
+- When used in the X300/X310 at frequencies below 1 GHz, it is necessary to
+  reduce the daughterboard clock rate to 20 MHz to achieve phase
+  synchronization and best RF performance (see \ref config_devaddr).
+
 \subsection dboards_tvrx TVRX
 
 The TVRX board has 1 real-mode frontend. It is operated at a low IF.
@@ -384,10 +393,29 @@ Sensors:
 -   **rssi**: float for measured RSSI in dBm
 -   **temperature**: float for measured temperature in degC
 
+Notes:
+
+- The TVRX2 requires a 64 MHz, 100 MHz or 200 MHz reference clock. On the X3x0,
+  set the daughterboard clock rate accordingly (see \ref config_devaddr), typically
+  to 100 MHz.
+
 \subsection dboards_e300 E310 MIMO XCVR board
 
 Please refer to \ref e3x0_dboard_e310.
 
+
+\subsection dboards_clock_rate Daughterboard reference clock
+
+The USRP motherboard provides a reference clock to the daughterboards, which
+the daughterboards will use to generate LO signals or anything else that
+requires a reference clock.
+
+The X3x0 has a programmable reference clock, which might have to be changed
+depending on various applications (see the daughterboard sections above).
+However, it can provide only one daughterboard clock per device, which can
+lead to conflicts. It might not be possible to use a specific daughterboard
+together with all others.
+
 \subsection dboards_dbsrxmod DBSRX - Modifying for other boards that USRP1
 
 Due to different clocking capabilities, the DBSRX will require
diff --git a/host/docs/usrp_x3x0.dox b/host/docs/usrp_x3x0.dox
index db19ca551..5f7284a09 100644
--- a/host/docs/usrp_x3x0.dox
+++ b/host/docs/usrp_x3x0.dox
@@ -18,6 +18,7 @@ More information:
 	- External 10 MHz input & output
 	- Expandable via 2nd SFP+ interface
 	- Supported master clock rates: 200 MHz and 184.32 MHz
+        - Variable daughterboard clock rates
 	- External GPIO Connector with UHD API control
 	- External USB Connection for built-in JTAG debugger
 	- Internal GPSDO option
@@ -430,6 +431,20 @@ Run the following commands:
 
 You must power-cycle the device before you can use this new address.
 
+\section x3x0_setup_clocking Setup Clocking
+
+\subsection x3x0_set_clocking_dboard Daughterboard clock
+
+The X3x0 provides a clock signal to the daughterboards which is used as a
+reference clock for synthesizers and other components that require clocks.
+There are daughterboards that require non-default clock values. See
+Section \ref config_devaddr on how to change the clock value, and \ref page_dboards
+for information specific to certain daughterboards.
+
+Not all combinations of daughterboards work within the same device, if
+daughterboard clock requirements conflict. Note that some daughterboards
+(e.g. the UBX) will try and set the daughterboard clock rate themself.
+
 \section x3x0_addressing Addressing the Device
 
 \subsection x3x0_addressing_singledev Single device configuration