Agilent Technologies SMPTE 310M Network Card User Manual


 
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Release Notes
Release Notes
This section describes two SMPTE 310M interface constraints that may affect
your test. It includes a description of the problem along with a simple solution or
workaround.
Initial startup with
sparse streams
Upon initial startup or when you make a large bit rate change, the SMPTE 310M
receiver may not synchronize if the stream contains large continuous strings of 1’s
or 0’s. This could happen if you are receiving many NULL packets with an all-1 or
all-0 payload (for example, from an idle SPI transmitter). You will notice many Rx
Psync and Rx Clock errors from the SPI LIF dialog.
The problem occurs because the stream does not contain enough variation in bit
values for the SMPTE 310M interface to unambiguously determine the bit rate.
For example, it will not be able to differentiate a stream consisting of all 0’s at 40
Mb/s (where the bit has one transition) from a stream consisting of all 1’s at 20
Mb/s (where the bit has two transitions).
The solution is to play a stream that contains transport stream packets carrying
real data until synchronization occurs. Without changing the bit rate, play the
original stream again. The SMPTE 310M interface will remember the bit rate and
correctly synchronize.
Large bit rate changes Because the SMPTE 310M interface implements a wide-band clock recovery
circuit, large bit rate changes (greater than 1 1/2 times the original rate) may
cause the SMPTE 310M receiver to lose synchronization. For example, this could
happen if you change from a bit rate of 22 Mb/s (with the interface correctly
synchronizing) to a bit rate of 40 Mb/s. If this occurs, you will notice many Rx
PSync and Rx Clock errors from the SPI LIF dialog.
You can avoid this situation by first changing to an intermediary value (for
example, 30 Mb/s). Once the interface is in synchronization, increase the rate.
Alternatively, you can disconnect the cable for a brief period, then reconnect it.
The SMPTE 310M interface will achieve synchronization after a few seconds.
If the problem still occurs, you may be receiving large continuous strings of 1’s or
0’s. As described in the problem above, play a stream containing real data at the
desired bit rate, then play the original stream again using the same rate. The
SMPTE 310M interface will remember the bit rate and correctly synchronize.