how to write data into a FIFO, directly, in a XOP app

I am looking for an example of how to write data into a FIFO, directly, in my XOP app.

In the XOP manual, it is stated that this is possible, but it is totally undocumented and out-dated.

I need this because my app has to stream rapidly and periodically an indeterminate amount of data.

I will appreciate any hint! Thank you very much in advance!