Basic Strategy:
I'm trying to measure in-cylinder pressure of an IC engine using a cRio (NI 9205 for pressure, NI9411 for encoder). We're using a quadrature encoder so pressure data can be recorded with respect to engine time (ie crank angle degrees). The FPGA writes pressure data to a FIFO each time it receives an A pulse (720/revolution). One engine cycle is two revolutions so a complete data set is 1440 points in the FIFO buffer. The RT VI waits until there are the correct number of points in the buffer and then reads the FIFO.
Issue:
This strategy works when the engine speed is less than 1600 rpm and a display on the RT shows a perfect pressure trace for each cycle. At anything greater than 1600 rpm the pressure trace begins to drift wrt crank angle degrees. To me this indicates that the FPGA is missing an A pulse meaning it takes longer for the FIFO buffer to reach 1440 data points.
Questions:
Is it possible that the FPGA/9205 is not fast enough to capture each A pulse and write a data point?
Is this a sound strategy for transferring data from the FPGA to the RT VI?
Is it possible that the FPGA is sensing every A pulse but cannot write data because the RT is querying the FIFO?
Any suggestions for how to fix this would be greatly appreciated. Thank You.
FPGA_Main.vi
rt_main.vi
