Packet-sized control transfers broken

[lealanko-rt]

Something goes wrong when the size of an IN control transfer is an exact multiple of the packet size (64 bytes). This is perhaps easiest to test by trying out a string descriptor that is 31 characters long. I haven't investigated exactly what happens, but I suspect that two zero-length packets are sent when only one is mandated.

The easiest way to fix this is to change < to <= in https://github.com/im-tomu/tomu-bootloader/blob/master/toboot/usb_dev.c#L242 but I believe it's also possible to get rid of require_zlp altogether so then the current comparison is correct: the packet is last if it is not full.

Unless I'm missing something, there's also another issue: according to USB 1.1 section 5.5.3, a zero-length packet should not be sent after the last packet, if data_p->len == len_asked, even if the the last packet is full.

Presumably these situations have never come up so far, so they are hardly critical, but they are certainly nasty pitfalls in waiting.