Atmel SAM4L Xplained Pro Evaluation Kit Atmel ATSAM4L-XPRO ATSAM4L-XPRO Scheda Tecnica

42023E–SAM–07/2013

Figure 19-1. Asynchronous Timer Block Diagram

In order to use this module, other parts of the system must be configured correctly, as described
below.

When the AST is enabled, it will remain clocked as long as its selected clock source is running. It
can also wake the CPU from the currently active sleep mode. Refer to 

 for details on the different sleep modes. 

The clock for the AST bus interface (CLK_AST) is generated by the Power Manager. This clock
is turned on by default, and can be enabled and disabled in the Power Manager.

A number of clocks can be selected as source for the internal prescaler clock CLK_AST_PRSC.
The prescaler, counter, and interrupt will function as long as this selected clock source is active.
The selected clock must be enabled in the System Control Interface (SCIF). 

The following clock sources are available:

• System RC oscillator (RCSYS oscillator). This oscillator is always enabled, except in some 

sleep modes. Refer to 

 for the 

characteristic frequency of this oscillator.

• 32kHz clock (OSC32 or RC32). The oscillator must be enabled before use. Selection 

between OSC32 and RC32 is done inside the Backup Power Manager module.

32-bit 

Prescaler

32-bit 

Counter

Alarm

Interrupts

COUNTER 

VALUE

CLK_AST_CNT

OVF

CONTROL 

REGISTER

EN

CSSEL

PSEL

Periodic 

Interrupts

ALARM 

REGISTER

Interrupt 

Status 

and 

Control

IRQs

PERIODIC 
INTERVAL 

REGISTER

Events

Wake 

Control

Wake

WAKE ENABLE 

REGISTER

DIGITAL 

TUNER 

REGISTER

RCSYS

OSC32

APB clock

GCLK

others

CLK_AST

CLK_AST_PRSC

CLK_AST

CLK_AST