ASF supports ARM's Cortex Microcontroller Software Interface Standard (CMSIS)
» Peripheral Register and Interrupt Definitions: a consistent interface for device registers and interrupts
» Core Peripheral Functions: access functions for specific processor features and core peripherals
» DSP Library: optimized signal processing algorithms and for Cortex-M4 support of SIMD instructions
CMSIS layer is included in Atmel Studio ARM toolchain and as a standalone package.
Detailled information on CMSIS can be found here.