Blocking read using NiFpga_ReadFifoU32 and a timeout

[daowens]

Greetings,

I'm accessing a FlexRIO 7954R card using the Linux C API generated from an FPGA bitfile that supports several 422 channels.  Data from each serial port is queued in a FIFO and retrieved with calls to NiFpga_ReadFifoU32().  When I call the ReadFifoU32 function with a non zero timeout I see my thread wait the appropriate amount of time before returning when no data was in the FIFO but the CPU utilization goes to 100%.  Is ReadFifoU32 simply busy waiting during the specified timeout period?  If so, is there a method in the C API that will actually block the calling thread?

Thanks,

Dave

[Michael G]

Hi daowens.

Long story short, this is expected behavior to a certain degree.  Typically speaking, the host will poll the FIFO as fast as possible.  There is a KnowledgeBase article that speaks to a similar situation with the interaction between an FPGA target and an RT target that may provide you with further information.

AE KB 4X1GBJDK: Why is My Real-Time CPU at 100% When Reading from a DMA FIFO (FPGA)?

I hope this information helps.

Regards,

Michael G.