[aq1018]

• a device reads a frame whose status is not Request, consumes its payload and CRC without checking, and listens again at once; before, it ran the bit-bang CRC over every heard reply and missed the host's next request, which follows a reply after about 73 us on a USB host (several bootloaders on one bus, rate independent)
• an unaddressed bootloader never answers a heard reply either
• the host read path still validates every reply
• the USART pin switches to its function after the transmitter is enabled, so the wire no longer sees a short low at every boot
• shared bus guide: the device turnaround rule for hosts
• protocol 0.5.2, core 0.6.3, ch32 0.7.2; V003 heaviest unchanged, V00x boot +4 B