Lagging BPod console display with "high-frequency" out TTL signal

AurelieP

Hi Josh,
I'd like to send a 200 Hz (AcqRate) output TTL signal through one of the BNC ports.
I use the following code:
sma = SetGlobalTimer(sma, 'TimerID', 2, 'Duration', 0.001, 'OnsetDelay', 0, 'Channel', 'BNC2', ...
'OnsetValue', 1, 'OffsetValue', 0, 'LoopMode', 1, 'EventsEnabled', 1, 'LoopInterval', (1/S.GUI.AcqRate) - 0.001);
When running the BPod protocol containing the above timer, the BPod console display lags by several seconds from the very beginning of the start of the BPod protocol, that includes state name display and button displays (green/black color switch).
There is no such display issue at frequencies up to ₁₉₀ Hz.
Although this problem is not critical for running the Bpod protocol it is very impractical to follow what the animal does in real-time.
I am using BPod machine r2, firmware v23, and BPod software 1.81 in Matlab 2021b.
Thanks!
Aurelie

Josh

Hello Aurelie,

The behavior you're seeing is by design. Each update of a MATLAB graphics object has a significant time cost. Each BNC event requires the BNC button to show the green graphic (on the rising edge of the TTL) and the red one (on the falling edge of the TTL). When events come fast enough, MATLAB can be effectively paralyzed trying to update the GUI graphics, and unable to process incoming events, resulting in a USB buffer overflow and a crashed session. To avoid this, GUI updates are suspended when events are received at a rate MATLAB can't handle.

That being said, we chose a conservative threshold to ensure stability across different systems, and you may be able to safely adjust it. The relevant code is on line 285 of RunStateMachine.m, or line 632 of BpodTrialManager.m if your protocol uses BpodTrialManager instead of RunStateMachine.

if serialPortBytesAvailable < 250 BpodSystem.RefreshGUI; end

Please keep in mind that since this isn't a setting, you'll have to re-apply the mod each time you update the software.

I hope this helps,
Josh