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 Upon initial startup or when you make a large bit rate change, the SMPTE 310M

sparse streams 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.