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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
If a clock is found from the two possible sources above, the boot program checks to verify that
the frequency is one of the supported external frequencies. If the frequency is one of the sup-
ported external frequencies, USB activation is allowed, else (no clock or frequency other than
one of the supported external frequencies), the internal 12 MHz RC oscillator is used as main
clock and USB clock is not allowed due to frequency drift of the 12 MHz RC oscillator.
23.4
Device Initialization
Initialization follows the steps described below:
1.
Stack setup
2.
Setup the Embedded Flash Controller
3.
External Clock detection (crystal or external clock on XIN)
4.
If external crystal or clock with supported frequency, allow USB activation
5.
Else, does not allow USB activation and use internal 12 MHz RC oscillator
6.
Main oscillator frequency detection if no external clock detected
7.
Switch Master Clock on Main Oscillator
8.
C variable initialization
9.
PLLA setup: PLLA is initialized to generate a 48 MHz clock
10. Disable the Watchdog
11. Initialization of UART0 (115200 bauds, 8, N, 1)
12. Initialization of the USB Device Port (in case USB activation allowed)
13. Wait for one of the following events
a.
Check if USB device enumeration has occurred
b.
Check if characters have been received in UART0
14. Jump to SAM-BA Monitor (see
Summary of Contents for SAM4S Series
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