clearing cached PYNQ metadata

Sometimes when you switch firmwares (you had one bitstream loaded, then you load a different one) the PYNQ "PL server" will not recognize that you changed firmwares, it will try to reuse the cached metadata (the HWH file) from the old firmware. The effect is that PYNQ will try to run the new bitstream with the old HWH - if the firmwares are sort of similar this can cause subtle problems, if they are very different you may get an OS crash or reboot.

It's not obvious when exactly this happens - it seems to be more common when the old and new firmwares had the same file path or file name?

This only happens under v3.0 of the PYNQ library, and is probably this problem: https://github.com/Xilinx/PYNQ/issues/1409

To manually clear the cache (rebooting works too):

import pynq
pynq.pl_server.global_state.clear_global_state()