[gregsadetsky]

TLDR - GLKVM's kernel emits a trailing 0-byte DATA packet (ZLP) (which PiKVM does not)

Supposedly, this is due to the `req->zero = ((count % maxpacket) == 0)` line in the kernel's f_hid.c - which, for 8-byte HID keyboard reports, makes it append a trailer packet. Strict BIOS HID stacks treat this 0-byte packet as malformed and beep.

[JdeBP]

Interesting. My first thought is wondering whether the keyboard HID is adding report IDs to its input reports, because it isn't in boot mode or something. That would have that effect.

[trumpdong]

Isn't that expected in USB so the receiving side knows it's at the end of the data transfer?