USB OTG FS (CDC-ACM): things to take care off while filling TX FIFO's

[MSuhe]

Is there anything to be taken care off while filling the TX FIFO's on USB OTG FS with STM32F411.

We observe an issue where the device seems to lock up, waiting for the TX done interrupt to fire. And while browsing i have found some posts where people have come across issues while filling TX FIFO's.