Atmel SAM4S Series, Preliminary Data Sheet

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486
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
27.2.7 USB Clock Controller
The user can select the PLLA or the PLLB output as the USB Source Clock by writing the USBS
bit in PMC_USB. If using the USB, the user must program the PLL to generate an appropriate
frequency depending on the USBDIV bit in PMC_USB.
When the PLL output is stable, i.e., the LOCK bit is set:
• The USB device clock can be enabled by setting the UDP bit in PMC_SCER. To save power
on this peripheral when it is not used, the user can set the UDP bit in PMC_SCDR. The UDP
bit in PMC_SCSR gives the activity of this clock. The USB device port requires both the 48
MHz signal and the Master Clock. The Master Clock may be controlled by means of the
Master Clock Controller.
Figure 27-7. USB Clock Controller
27.2.8 Peripheral Clock Controller
The Power Management Controller controls the clocks of each embedded peripheral by means
of the Peripheral Clock Controller. The user can individually enable and disable the Clock on the
peripherals.
The user can also enable and disable these clocks by writing Peripheral Clock Enable 0
(PMC_PCER0), Peripheral Clock Disable 0 (PMC_PCDR0), Peripheral Clock Enable 1
(PMC_PCER1) and Peripheral Clock Disable 1 (PMC_PCDR1) registers. The status of the
peripheral clock activity can be read in the Peripheral Clock Status Register (PMC_PCSR0) and
Peripheral Clock Status Register (PMC_PCSR1).
When a peripheral clock is disabled, the clock is immediately stopped. The peripheral clocks are
automatically disabled after a reset.
In order to stop a peripheral, it is recommended that the system software wait until the peripheral
has executed its last programmed operation before disabling the clock. This is to avoid data cor-
ruption or erroneous behavior of the system.
The bit number within the Peripheral Clock Control registers (PMC_PCER0-1, PMC_PCDR0-1,
and PMC_PCSR0-1) is the Peripheral Identifier defined at the product level. The bit number cor-
responds to the interrupt source number assigned to the peripheral.
27.2.9 Free Running Processor Clock
The Free Running Processor Clock (FCLK) used for sampling interrupts and clocking debug
blocks ensures that interrupts can be sampled, and sleep events can be traced, while the pro-
cessor is sleeping. It is connected to Master Clock (MCK).
USB
Source
Clock
UDP Clock (UDPCK)
UDP
USBDIV
Divider
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