Prime slows down when connected to PC

[cyrille de brébisson]

Hello,

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!

Cyrille