gets some data from the fifo
| fifo, |
| || buf, |
| || n|
address of the fifo to be used
pointer to the storage buffer
max. number of elements to get
This macro get the data from the fifo and return the numbers of elements
copied. The data is not removed from the fifo.
Note that with only one concurrent reader and one concurrent
writer, you don't need extra locking to use these macro.