Inconsistent free Flash memory between ATmega2560 and ATmega2561 when using a bootloader

[gudnimg]

Hi I noticed this issue before v3.1.0

When I build/compile PIO shows total flash memory:

• ATmega2561 shows: 261120 bytes
• ATmega2560 shows: 253952 bytes (8192 has been subtracted)

I'm not familiar where these numbers are calculated but I would think the flash storage should look exactly the same. Only difference between the chips is ATmega2561 has fewer physical pins.

Here is my platformio.ini settings:

[env]
platform = atmelavr
framework = arduino
monitor_speed = 115200

board_build.f_cpu = 16000000L
board_hardware.uart = uart0
board_hardware.oscillator = external

upload_flags = -Pusb

platform_packages = 
    toolchain-atmelavr

[env:megaatmega2561]
board = ATmega2561
board_build.mcu = atmega2561

[env:megaatmega2560]
board = megaatmega2560
board_build.mcu = atmega2560

[gudnimg]

I looked into arduino.py and I think the problem is ATmega2560 is not considered to be any of "MiniCore", "MegaCore", "MightyCore", "MajorCore" So maybe this isn't an issue at all? Why is there such a big difference in bootloader sizes? 🤔

[MCUdude]

Hi! board = megaatmega2560 is probably the Arduino MEGA 2560 board. I'll assume you want to use the MegaCore implementation? Try using board = ATmega2560 instead.

The MEGA2560 board uses a bootloader where 8192 bytes of flash are allocated for it. MegaCore does not allocate any flash memory for a bootloader if you haven't specified in the platformio.ini file that a bootloader is used.

[gudnimg]

Thanks! I'm closing this issue since this isn't a bug 👍