On Wed, Mar 10, 2021 at 09:56:04PM +0100, Matthias Schwarzott wrote:

quoted

What happens if you set the value to 1000 before running the test?

I tested different values. At 1000 it still disconnects. At lower values it
no longer does this.
I tested 200 up to 900. Even 900 ms is good enough to keep it connected.

Btw. it is not a USB disconnect, but it just seems to plays medium ejected.

Out of interest I called "sg_start -v -l /dev/sde" after one of the failing
experiments. That made the Kindle go back to connected state.

To me the above experiments show that enough TEST UNIT READY commands are
needed in the 2 s after a SYNCHRONIZE CACHE.

So you have found the solution to your problem.  Congratulations!

Alan Stern