Updated Mighty-1284p v1.6.3 repo today:
• added support for variant "Sleeping Beauty"
• updated boards.txt.alt to include menu options for enabling/disabling JTAG, as well as A4/A5 functionality for Sleeping Beauty
• updated boards.txt.alt clock speed options to disallow bootloader options that flash LED on PB7 for boards that do not have the board LED connected to PB7
• added platform.local.txt to restore Mighty-1284p separator heading in Tools|Board list
Thanks to Bill (bperrybap) for providing the variant file pins_arduino.h for "Sleeping Beauty" board.
boards.txt.alt has been extended, with more menu options added - JTAG enable/disable (all boards), A4/A5 pin function select (Sleeping Beauty only).
Clock speed for boards that do not have a board LED attached to PB7 have had bootloader options that flash the LED using that pin have been removed from the boards.txt.alt menu. This affects avr_developers and the original "maniacbug" Mighty-1284p layouts.
The issue is that "optiboot_atmega1284p.hex" is currently the only bootloader file in the "bootloaders" directory that has the LED flash on bootloader startup disabled. For compatibility across the different board types, all bootloaders should have the LED flashing disabled, otherwise some boards may be getting unexpected toggling of the PB7 pin, which may be appear as a bug.
After some discussion last year, it was decided the preferred approach would be to simply disable the LED flash on all bootloaders for Mighty-1284p, but unfortunately it is now evident this was only actually done for one version of the bootloader, not all.
To fix this would require rebuilding the bootloaders, possibly renaming them with an appended "_NO_LED" for additional clarity. It may also be an opportunity to update optiboot.c to the latest version -- the current optiboot.c Makefile is out of date for the current avr-gcc tools. (Thanks to Bill for uncovering these issues and bringing them to my attention.)
Volunteers for the "clean up the Mighty-1284p bootloaders/optiboot directory" project welcome. 