Datasheet

101
SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
14. Real-time Timer (RTT)
14.1 Overview
The Real-time Timer is built around a 32-bit counter and used to count elapsed seconds. It generates a periodic
interrupt and/or triggers an alarm on a programmed value.
14.2 Embedded Characteristics
 32-bit Free-running backup counter
 Alarm Register capable to generate a wakeup of the system
14.3 Block Diagram
Figure 14-1. Real-time Timer
14.4 Functional Description
The Real-time Timer is used to count elapsed seconds. It is built around a 32-bit counter fed by Slow Clock divided
by a programmable 16-bit value. The value can be programmed in the field RTPRES of the Real-time Mode
Register (RTT_MR).
Programming RTPRES at 0x00008000 corresponds to feeding the real-time counter with a 1 Hz signal (if the Slow
Clock is 32.768 Hz). The 32-bit counter can count up to 2
32
seconds, corresponding to more than 136 years, then
roll over to 0.
The Real-time Timer can also be used as a free-running timer with a lower time-base. The best accuracy is
achieved by writing RTPRES to 3. Programming RTPRES to 1 or 2 is possible, but may result in losing status
events because the status register is cleared two Slow Clock cycles after read. Thus if the RTT is configured to
trigger an interrupt, the interrupt occurs during 2 Slow Clock cycles after reading RTT_SR. To prevent several
SLCK
RTPRES
RTTINC
ALMS
16-bit
Divider
32-bit
Counter
ALMV
=
CRTV
RTT_MR
RTT_VR
RTT_AR
RTT_SR
RTTINCIEN
RTT_MR
0
10
ALMIEN
rtt_int
RTT_MR
set
set
RTT_SR
read
RTT_SR
reset
reset
RTT_MR
reload
rtt_alarm
RTTRST
RTT_MR
RTTRST