🛠 Porting an AVR Uno sketch to the Renesas core

Goal

Move a working AVR Uno sketch to the R4 Minima. The core is ArduinoCore-renesas, a completely different architecture, so anything AVR-specific must go.

Porting checklist

1. AVR registers and headers: avr/interrupt.h, avr/pgmspace.h, direct SFR writes (DDRB, TCNT1...) do not compile ; replace with Arduino APIs or the RA HAL.
2. Integer width: int is 32 bits on Cortex-M4 vs 16 on AVR ; bit-packed math and overflow assumptions change behavior.
3. analogWrite semantics: with a true 12-bit DAC present, resolutions differ from the AVR's 8-bit PWM - call analogWriteResolution explicitly on every analogWrite/analogRead path.
4. Drive strength: GPIO are limited to 8 mA (versus 20 mA on the AVR Uno) ; relays, LED arrays and loud piezos need a transistor or driver.
5. Libraries: prefer ones updated for the Renesas core ; a library that pokes registers needs porting, not just a version bump.

Expected result

Most pure-Arduino-API sketches compile unchanged ; the failures cluster exactly on the five points above.

Gotchas

• Re-test timing: delay/micros still work, but tight timer tricks and 16 MHz assumptions change at 48 MHz.