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Full Version: Prime slows down when connected to PC
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today I noticed that my Prime slows down when connected to my pc. I'm developing a program to design Butterworth and Chebyshev filters. When the prime is connected via USB calculations get slower and the screen starts to be laggy (especially when moving around in a plot view). When disconnected everything work as usual.

This is likely due to the screen updating since the connectivity kit also keeps track of changes on the screen. Does it help when you close out the screen preview pane in the connectivity kit?
I don't use the screen preview on the connectivity kit. It might be that the screen stream is always open in background?

No, the screen stream is not happening in the background, but USB packets are being continuously sent back and forth.

With the latest version, the USB protocol changed.

In order to avoid driver development on the computer, HP Prime registers to the PC as a HID device (because windows has build in drivers for those)...

The conn kit can then interface with the windows HID drivers and exchange data with the calculator...

However, we discovered that windows does not "think" the HID packet are important. As a result, windows will regularly "drop" HID packet (discard them without telling the app)...

This of course was causing transfer failures (and lots of frustration).

As a result, the PC to calc protocol was changed to be a "ping/pong" protocol where the PC tells the calc: Do you have anything for me? If yes, you have 500ms to send me the data and then it is my turn.
Then the calc send data (if any) for up to 500ms, and they replies back: do you have anything for me? if yes, you have 500ms to send it.
And the PC answers (like the calc)...

And so forth...

This results in continuous sending/receiving of USB packets from the PC to the calc. And on the calc, this takes CPU power.

So, long story short, if your calc slows down when USB is connected, blame windows!

Ok, I got the point. Thanks!
Cyrille, est-ce que j'ai raison de penser que l'horloge de la calculatrice est synchronisée sur le PC lors de la connexion USB? J'ai fait un réglage pifométrique de l'heure quand j'ai mis ma Prime en service la semaine dernière et maintenant j'aperçois qu'elle est pile à l'heure.

Am I right in thinking that the calculator's clock is synchronised to the PC when connected over USB? I set the clock approximately when I first set it up last week and I now see that it's dead on.



Big Grin

Hooray! I get to do it too!
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