USB Project (15th August)

Ian Coulter

Last Week

• Needed to work error flags and error counting into labview. This seems to work successfully but doesn’t work for continuous DAQ mode as we still can’t stop it

• Created several different DLL projects as it was annoying having to change between the various different types

Problem

• The FIFO fills up quickly for anything faster than one channel averaging over two samples on continuous mode as it reads data out faster than we can read it

• When the FIFO is full, we lose large chunks of data

Problem

• This is due to the code– taking in all the data– manipulating the data to a readible form– writing it to file

then looping round again

• The manipulation and writing to file takes a long time during which the FIFO overflows

Solution

There are two possible ways to solve this:

– Introduce multi-threading so the program reads the data from the USB at the same time as it writes it to file

– Strip down the manipulation of the data before it is written to file

Multi-threading

• Split the code so it goes to two threads:– The sender thread takes in the data and

sends it to a circular buffer– The receiver thread reads the data from this

buffer and sends it to a file

• Can’t seem to find a way to do this without using the buffer which slows it down

Multi-Threading

• Even with the binary file writing this process is still slow due to the writing to a buffer necessary to transfer data between the threads

• The fastest I could get this to work was one channel averaging over four samples. This is half as good as before.

Binary

• Removed all data manipulation so that the data is written straight to file

• We can use another C code or Labview to read the raw data from this data file and combine the bytes to give out meaningful data into another text file

Binary

• This works really well!

• Can now read much much faster. Can read up to four channels at full speed without data loss or the FIFO filling up

• The maximum possible speed is seven channels at full speed so this is good!