AT32UC3L064_1 ATMEL [ATMEL Corporation], AT32UC3L064_1 Datasheet - Page 142

• Manufacturer Part Number: AT32UC3L064_1
• Description: AVR32 32-bit Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

11.5
32099A–AVR32–06/09
Application Example
Certain events are known as asynchronous peripheral events, as identified in
page
user peripherals. The clock will be restarted for this module only, without waking the system from
sleep mode. The clock remains active only as long as required by the triggered function, before
being switched off again, and the system remains in the original sleep mode. The CPU and sys-
tem will only be woken up if the user peripheral generates an interrupt as a result of the
operation. This concept is known as SleepWalking
Power Manager chapter. Note that asynchronous peripheral events may be associated with a
delay due to the need to restart the system clock source if this has been stopped in the sleep
mode.
This application example shows how the Peripheral Event System can be used to program the
ADC Interface to perform ADC conversions at selected intervals.
Conversions of the active analog channels are started with a software or a hardware trigger.
One of the possible hardware triggers is a peripheral event trigger, allowing the Peripheral Event
System to synchronize conversion with some configured peripheral event source. From
11-1 on page
eral event, or an event from the PWM Controller. The AST can generate periodic peripheral
events at selected intervals, among other types of peripheral events. The Peripheral Event Sys-
tem can then be used to set up the ADC Interface to sample an analog signal at regular
intervals.
The user must enable peripheral events in the AST and in the ADC Interface to accomplish this.
The periodic peripheral event in the AST is enabled by writing a one to the corresponding bit in
the AST Event Enable Register (EVE). To select the peripheral event trigger for the ADC Inter-
face, the user must write the value 0x7 to the Trigger Mode (TRGMOD) field in the ADC
Interface Trigger Register (TRGR). When the peripheral events are enabled, the AST will gener-
ate peripheral events at the selected intervals, and the Peripheral Event System will route the
peripheral events to the ADC Interface, which will perform ADC conversions at the selected
intervals.
Figure 11-2. Application Example
Since the AST peripheral event is asynchronous, the description above will also work in sleep
modes where the ADC clock is stopped. In this case, the ADC clock (and clock source, if
needed) will be restarted during the ADC conversion. After the conversion, the ADC clock and
clock source will return to the sleep state, unless the ADC generates an interrupt, which in turn
will wake up the system. Using asynchronous interrupts thus allows ADC operation in much
lower power states than would otherwise be possible.
141. These can be issued even when the system clock is stopped, and revive unclocked
AST
Periodic peripheral
141, it can be read that this peripheral event source can be either an AST periph-
event
Peripheral
System
Event
™
and is described in further detail in the
Interface
ADC
AT32UC3L
Table 11-1 on
Table
142