SAM4L Datasheet, PDF (156/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
12.5 Product Dependencies
In order to use this module, other parts of the system must be configured correctly, as described
below.
12.5.1
Power Management
The 32 kHz oscillators (RC32K and OSC32K) are not turned off in Power Save modes. BODs
are turned off in some Power Save modes and turned automatically on when the device wakes
up. The Voltage Regulation System is controlled by the BPM, refer to Section 11. ”Backup
Power Manager (BPM)” on page 133 for details.
12.5.2 Clocks
The BSCIF controls the 32kHz oscillators as well as the 1MHz RC in the device. The oscillators
can be used as source for the CPU and peripherals, selection of source is done in the Power
Manager. The oscillator can also be used as source for generic clocks. Device modules using a
32 kHz clock must choose between the 32 kHz crystal oscillator and the RC 32 kHz oscillator for
the clock source. Setting the CK32S bit to one in the PMCON register (PMCON.CK32S) will
select the RC32K oscillator as the 32 kHz clock source, and leaving it to zero will select the 32
kHz crystal oscillator output.
12.5.3 Interrupts
The BSCIF interrupt request line is connected to the NVIC. Using the BSCIF interrupt requires
the NVIC to be programmed first.
12.5.4
Debug Operation
The BSCIF does not interact with debug operations.
12.6 Functional Description
12.6.1
32KHz Oscillator (OSC32K) Operation
Rev: 2.0.0.0
The 32KHz oscillator operates as the standard main oscillator. The 32KHz oscillator can be
used as source clock for the Asynchronous Timer (AST), the Watchdog Timer (WDT) and the
Brown Out Detectors (BODs) when they are used in sampling mode. The 32KHz oscillator can
also be used as source for the generic clocks.
The oscillator is disabled by default after reset.
The oscillator is enabled by writing a one to the OSC32 Enable bit in the 32KHz Oscillator Con-
trol Register (OSCCTRL32.OSC32EN). The oscillator is disabled by writing a zero to the
OSC32EN bit, while keeping the other bits unchanged. Writing to OSC32EN while also writing to
other bits may result in unpredictable behavior. Operation mode (external clock or crystal) is
selected by writing to the Oscillator Mode bit in OSCCTRL32 (OSCCTRL32.MODE). The oscilla-
tor is an ultra low power design and remains enabled in all Power Save Modes.
The start-up time of the 32KHz oscillator is selected by writing to the Oscillator Start-up Time
field in the OSCCTRL32 register (OSCCTRL32.STARTUP). The BSCIF masks the oscillator
output during the start-up time, to ensure that no unstable clock cycles propagate to the digital
logic.
The OSC32 Ready bit in the Power and Clock Status Register (PCLKSR.OSC32RDY) is set
when the oscillator is stable and ready to be used as clock source. An interrupt can be gener-
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