/diy/ - Do It Yourself

>>2393346
>AtMega1284
Are those even in stock? That's a pretty high-spec machine as far as 8-bit micros go. I'd lean towards the more modern but slightly lower spec model that is the 4808/4809, or else jump to a 16 or 32-bit micro. 520kB of RAM on an ESP32 for like $2 man, that's fucking value, plus its castellated vias are kinda easy to solder. But that's just me. Maybe you're one of those "tht parts only" kinda guys who loves sockets and has never heard of ICSP.
As for the XTAL pins, they aren't labelled as PB1/PC5/etc. and the description for the pins only mentions the crystal, so I'm 99% sure they can only be used for the crystal. Not as GPIOs.
>XTAL1: Input to the inverting Oscillator amplifier and input to the internal clock operating circuit
>XTAL2: Output from the inverting Oscillator amplifier
Pic related is an inverting oscillator amplifier. It has its own internal RC oscillator so you don't HAVE to use the crystal, but you'll be limited to 8MHz instead of 20MHz.

Also note that getting a bootloader onto the micro (the one from MightyCore) will require an external programmer or using an arduino as ISP. I'd program it through a USBasp instead of through the bootloader either way, because not having a USB-to-UART module on the board saves space. Sure serial printing can help debugging noob codes, but once you're caring about discrete clock cycles you find that the delays and buffering involved with the serial printing become unusable. If you actually cared about debugging you'd use Atmel Studio or MPLAB X and use a proper programmer with in-circuit debugging. IIRC there's a GNU licensed tool or two that does debugging for AVRs, designed to work alongside AVR-GCC and AVRdude, but I can't say whether it will be good.
Also, external USB-to-UART cable things are a dime a dozen and pretty handy, be sure to buy or make one that supports switching between 5V and 3.3V.

Any particular features you want to shove on the dev-board?
>see also:
>>>/diy/mcg