SAM4L Datasheet, PDF (445/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
19. Asynchronous Timer (AST)
Rev: 3.1.1.1
19.1 Features
• 32-bit counter with 32-bit prescaler
• Clocked Source
– System RC oscillator (RCSYS)
– 32KHz clock (OSC32 or RC32)
– APB clock
– Generic clock (GCLK)
– 1KHz clock (OSC32 or RC32)
• Operation and wakeup during backup
• Optional calendar mode supported
• Digital prescaler tuning for increased accuracy
• Periodic interrupt(s) and peripheral event(s) supported
• Alarm interrupt(s) and peripheral event(s) supported
– Optional clear on alarm
19.2 Overview
The Asynchronous Timer (AST) enables periodic interrupts and periodic peripheral events, as
well as interrupts and peripheral events at a specified time in the future. The AST consists of a
32-bit prescaler which feeds a 32-bit up-counter. The prescaler can be clocked from different
clock sources, including the low-power 32kHz oscillator, which allows the AST to be used as a
real-time timer with a maximum timeout of more than 100 years. Also, the PB clock or a generic
clock can be used for high-speed operation, allowing the AST to be used as a general timer.
The AST can generate periodic interrupts and peripheral events from output from the prescaler,
as well as alarm interrupts and peripheral events, which can trigger at any counter value. Addi-
tionally, the timer can trigger an overflow interrupt and peripheral event, and be reset on the
occurrence of any alarm. This allows periodic interrupts and peripheral events at very long and
accurate intervals.
To keep track of time during backup mode the AST can run while the core is powered off. This
will reduce the power consumption when the system is idle. The AST can also wake up the sys-
tem from backup mode using either the alarm wakeup, periodic wakeup. or overflow wakeup
mechanisms.
The AST has been designed to meet the system tick and Real Time Clock requirements of most
embedded operating systems.
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