Many times, internal peripherals in a MCU are enough to handle basic operations, like GPIOs, ADCs, DACs, etc. However, for complex applications, extensions for such peripherals are needed, and actually widely used in industry.

Since RIOT aim is to keep the periph interfaces as slim and portable as possible, making extensions to them is indeed a complicated task. The aim of this issue is to explore the possible solutions to this, and to work together towards a common definition on how to write APIs and driver extensions for this use-case.

I'll summarize here the interfaces that need changes, and the PRs if there's one.

GPIO

• periph/gpio: support for extension API #9860 (partially replaces drivers/gpio_exp: map GPIO expanders onto gpio_t #9190) (PR)
• periph/gpio: support for extension API (part 2) #9958 (partially replaces drivers/gpio_exp: map GPIO expanders onto gpio_t #9190) (PR)

ADC

• periph/adc: support for ADC extension API  #10527 (PR)

DAC

• periph/dac: support for DAC extension API #10512 (PR)

PWM

• periph/pwm: support for PWM extension API #10533 (PR)