Hi folks, After struggling for a day with the "stuck at 69%" problem, I finally reached the conclusion that intelligent folks like @Wacky already came to many months back -- the stock CDC bootloader just doesn't seem capable of flashing Marlin images larger than 64kb. Even compiling out SD support only gets me down to around 73k, not quite small enough. My understanding is that this is less a limitation of the CDC bootloader than it is of the avr109 protocol that it implements. My question is: is there a way to work around the CDC bootloader? @Wacky mentioned getting the LUFA HID bootloader working, but I didn't notice any specifics on getting that up and running. I can compile the LUFA HID bootloader myself, but I don't know if there are any configuration changes required to support the BWP. I have an STK500 that I can use for ISP programming in the meantime, but it sure is a pain.