ASF (Advanced Software Framework) is a reusable embedded software framework for Atmel/Microchip MCUs.

It provides drivers, services, middleware, board support, and application examples to speed up evaluation, prototyping, and production firmware work.

What ASF Provides

Low-level peripheral drivers (USART, SPI, TWI, ADC, TC, PWM, etc.)
Common services (IOPORT, GPIO, delay, serial, clock helpers, and others)
Board support files and ready-to-build example projects
CMSIS/device headers and register definitions for supported SAM devices

ASF Layer Model

ASF software layers

Typical ASF projects are organized in these layers:

Applications: end-user firmware logic and product features.
Services: reusable higher-level software blocks used by applications.
Components: support for external hardware blocks (display, memory, codecs, etc.).
Drivers: low-level MCU peripheral access (USART, SPI, TWI, ADC, timers, ...).
Boards: board-specific pin, clock, and peripheral mappings.
Utilities: shared helpers/macros/common infrastructure used across modules.

Repository Layout (High Level)

sam/: SAM device drivers, boards, utils, services, and applications
common/: cross-platform services/utilities used by multiple families
thirdparty/: bundled third-party middleware/components
avr32/, mega/, xmega/: ASF content for other MCU families

Documentation Sources

Package overview and ASF introduction: readme.txt
ASF release notes: asf-releasenotes-3.52.0.pdf
Module-level API/quickstarts: source Doxygen comments in each module
Layer image source: https://startingelectronics.org/software/atmel/asf-arm-tutorial/asf-layers.jpg

Notes

This documentation set is a curated subset focused on SAM4SD32/SAM4S-EK2. Some ASF references point to legacy Atmel URLs, but module source comments remain the primary reference for API and usage.