MegaCoreX VS AVR-Guidance

At the moment, I'm using MegaCoreX. I was on FastLED v3.3.3 but also tried v3.5 with the same issue.

See also the Atmega 4808/4809 parts: these are available in DIP packages, and are supported by a different Arduino Core, but are VERY close the the 328P. https://github.com/MCUdude/MegaCoreX

Howdy, I’ve built my own board with a 3208 which is in the same family as your 4808 and have been using MegaCoreX to program it through the Arduino IDE. You can use it to set functionality of the reset pin as well as BOD level and internal clock frequency.

MegaCoreX https://github.com/MCUdude/MegaCoreX An Arduino core for ATmega4809, ATmega4808, ATmega3209, ATmega3208, ATmega1609, ATmega1608, ATmega809 and ATmega808. "For programming, these chips use a UPDI programming interface."

https://github.com/MCUdude/MegaCoreX may be a useful starting point.

The ATmega4809 overview informs that it has 11 PWM peripherals. However, I'm not able to find 11 pins capable to generate a PWM signal, just 9. I have generated a PWM signal in all pins with Arduino IDE and analogWrite function and it confirms the ATmega4809 pinout described in the MegaCoreX library.

Use of MCUdude's MegaCoreX gives you a lot of flexibility, such as easily changing the clock frequency and allowing access to all the serial ports."

Check out the newer attiny chips......cheap, available, and LOW POWER. No external crystal or other components required. Programmable via Arduino IDE.,,see: https://github.com/SpenceKonde/megaTinyCore You can use any arduino as a programmer (JTAGTOUPDI) or make one with a cheap serial adapter: https://github.com/SpenceKonde/AVR-Guidance/blob/master/UPDI/jtag2updi.md

For Serial UPDI attach either a diode or resistor between RX and TX, then connect RX to UPDI PIN, along with and VCC and GND. https://github.com/SpenceKonde/AVR-Guidance/blob/master/UPDI/jtag2updi.md

I own a PICKIT4, so normally I would just breakout Vcc, Gnd, and UPDI pins and directly connect my PICKIT to it. This time though my friend recommended me to also include a SerialUPDI circuit on board to accommodate Arduino users (and ones without PICKIT in general). The part related to SerialUPDI are JP3, JP4, D35, and R5.

Yup, that should do the trick. You might want to give this guide a good read-through. It has some chip-specific tips (search for FTDI) and general recommendations for wiring and removing the Rx LED if it gives you troubles.

Choice of hardware

You can use RX/TX with the UPDI interface directly, see https://github.com/SpenceKonde/AVR-Guidance/blob/master/UPDI/jtag2updi.md. You should at least add a resistor on the line. Then you'll be able to program it with pymcuprog in serial mode, without a bootloader.

ISP looks a lot like spi. Updi is asynchronous uart. It's a lot different and I would recommend looking at serial updi.