Datasheet

AON Counters
Intel
®
Quark™ microcontroller D2000
Datasheet January 2016
474 Document Number: 333577-002EN
25 AON Counters
The SOC supports 2 Always On (AON) counters.
The first counter is an always on free running counter running off the 32kHz RTC
clock. The second is a periodic counter which allows a timer value to be loaded, and
an interrupt to fire when the timer expires.
25.1 Features
25.1.1 AON Counter
The following is a list of AON counters features:
• A free running up counter running off the 32,768Hz clock
• Can be enabled/disabled via software
• Can be used as a general purpose timer
• Can be used by SW for time-stamping samples received from the sensors/ADC
25.1.2 AON Periodic Timer
The following is a list of AON periodic timer features:
• Periodic counter running off the 32,768Hz clock
• AON Periodic Timer continuously decrements from a configured value
• AON Periodic Timer expires when the counter reaches 0
• When the AON Periodic Timer expires it reloads a configured value and
decrements
• The AON Periodic Timer is disabled by loading a value of 0, it is enabled by
loading a non 0 value
• Generates an alarm when the timer expires
The AON Control & Status registers are described in the previous chapter on the
System Control Subsystem
. The AON Periodic Timer configuration comes from the
system clock domain – the AON Periodic Timer is clocked using the RTC clock, so it
will take a number of core clocks for the AON Periodic Timer configuration to
propagate into the RTC clock domain. To program the AON Periodic Timer (i.e. clear
an alarm via the AONPT_CTRL.AONPT_CLR register bit or reset the counter value via
the AONPT_CTRL.AONPT_RST) the relevant control bit must be set by software and
then polled until it is cleared by hardware. At this point the desired configuration has
taken effect.
AON Periodic timer runs on RTC Clock. Whenever power is cycled, RTC Oscillator takes
time to lock and its lock time (< 2ms) is typically higher than Hybrid Oscillator (< 2
us) that provides the system clock. Thus CPU may start to execute much earlier,
before RTC oscillator has attained lock. For AON Periodic timer to be started through
AONPT_RST=1, RTC Clock has to be running already.