6 Message Reference
76
The PLL clock is used as the reference when acting as CT bus Primary Master.
If the clock is to be recovered from one of the line interfaces then the
highest-priority in sync line interface is used as the reference. Each line
interface is assigned a priority: by default liu_id=0 is the highest priority and
liu_id=7 the lowest. The user may modify the priority order by sending the
MVD_MSG_CLOCK_PRI message. If none of the interfaces are available for
recovery, then the phase locked loop runs in holdover mode, outputting a
clock with the same frequency as the last valid signal. When a valid signal
returns, it waits for a short period to verify that it is stable and then
automatically switches to use it as the clock reference.
If using one of the NETREF signals as the reference source, then another
board in the system must be providing this reference by driving a clock
source onto the appropriate CT bus NETREF lines. If the NETREF signal is lost,
the board continues with the PLL in holdover mode until another
MVD_MSG_CNFCLOCK message is received to switch to a new mode.
Note:
If the NETREF signal recovers, it is still necessary to re-set the clock configuration
and move out of holdover mode by sending MVD_MSG_CNFCLOCK and re-
selecting the appropriate mode.
ref1_mode
This parameter determines whether the CT bus NETREF_1 clock is driven onto
the CT bus by this board. The permissible values are as follows:
Value
NETREF_1 clock Mode
0 No
Change
1
Drive NETREF_1 using clock recovered from highest priority line
interface.
6
Tri-state (i.e., Not driven)
When the NETREF_1 signal is being driven then the clock source is the
highest priority line interface. If no interface is available for clock recovery,
then no signal is driven onto the bus.
Driving the NETREF_1 signal is independent of the clk_mode and pll_clk_src
settings for this board.
Status Response
The confirmation message (if requested) indicates success by status of zero.
On error, the following status value can be found in the confirmation
message.
Value
Mnemonic
Description
0xff
None
Request to configure clocking mode fails.
