Get data from the Stream Manager buffers.
- AK_DataReady : the buffer was granted
- AK_NoDataReady : the buffer is not granted yet (never happens when called with in_bWait flag)
- AK_NoMoreData : the buffer was granted but reached end of file (next call will return with size 0)
- AK_Fail : there was an I/O error
||Returned address of granted data space
||Returned size of granted data space
||Block until data is ready