Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Fiche De Données

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SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

The Boot Program implements the algorithm in 

The SAM-BA Boot program seeks to detect a source clock either from the embedded main oscillator with external
crystal (main oscillator enabled) or from a supported frequency signal applied to the XIN pin (Main oscillator in
bypass mode).

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 supported 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.

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 of the Watchdog

11. Initialization of UART0 (115200 bauds, 8, N, 1)

12. Initialization of the USB Device Port (in case of USB activation allowed)

13. Wait for one of the following events:

1.

Check if USB device enumeration has occurred

2.

Check if characters have been received in UART0

14. Jump to SAM-BA Monitor (see 

Device

Setup

Character # received

from UART0? 

Run SAM-BA Monitor

USB Enumeration 

Successful ?

Yes

Run SAM-BA Monitor

Yes

No

No