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How to tell 0 blocks found from no new blocks

Pixy Software
#1

From what I understand pixy.getBlocks returns the number of blocks found. However, returning 0 could mean 0 blocks found or no new blocks available since the last call. Before I realized this, this was causing me problems as I was trying something along these lines:

while(1)
{
    blocks=pixy.getBlocks()

    if (blocks >0)
    { 
        do some stuff if pixy sees what we want......
    }
    else 
    {
        do some stuff if pixy doesnt see what we are looking for
    }
}

However, it was not behaving as expected as blocks being equal to 0 could also mean no new frames available. The fix was easy, I simply put a delay in the loop to make sure the call to getBlocks() never executes more than 50 times per second.

However, is there an easy way to tell if a 0 returned means 0 blocks found or no new data?

#2

Hello David,
You are correct. This is something that the current serial protocol doesn’t support, and it’s something we’re going to address with a new (or tweaked) protocol (we just don’t have a release date yet!) But your workaround is what we’ve suggested. It’s guaranteed to get you the correct result.

Edward

#3

Is there fix or work around to this?

#4

Not sure if it has been fixed, but the workaround was pretty easy. I simply made certain I didnt call pixy.getBlocks() more than 30 times per second. You could probably get away with faster, but 30 worked well for me and my application.

#5

Hello David,
My apologies! It sounds like you figured this out, but there are a couple threads that describe a similar approach.

http://cmucam.org/boards/9/topics/5734?r=5758#message-5758

But basically you wait 20ms between frames, and that will guarantee that when you call getBlocks(), you’ll be getting the most recent frame.

Edward

#6

Thank you David and Edward