Error in USB data transmission


I have a USB device to which my driver transmits (donwstream) DV data. To
meet the framing rates for DV transfers i send NULL packets to the device.
The NULL packets are successfully transferred most of the times. But
sometimes, no OUT tokens are sent by host inbetween 2 SOF packets. For
example, if i request the bus driver to send 16 NULL packets then
1,2,4,5,6…16 packets are successfully sent to the device. But the 3rd
NULL packet is not transferred. This is happenning periodically. Can
anyone tell me how to make the bus driver send NULL packets correctly
without missing SOFs?

Any ideas/pointers on this will be highly appreciated!


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