SAM9260_14 Datasheet, PDF (77/784 Pages) ATMEL Corporation – AT91SAM ARM-based Embbedded MPU

13.3 Device Initialization
Initialization follows the steps described below:
1. FIQ Initialization
2. Stack setup for ARM supervisor mode
3. External Clock Detection
4. Switch Master Clock on Main Oscillator
5. C variable initialization
6. Main oscillator frequency detection if no external clock detected
7. PLL setup: PLLB is initialized to generate a 48 MHz clock necessary to use the USB Device. A register
located in the Power Management Controller (PMC) determines the frequency of the main oscillator and
thus the correct factor for the PLLB.
a. If Internal RC Oscillator is used (OSCSEL = 0) and Main Oscillator is active, Table 13-1 defines the
crystals supported by the Boot Program when using the internal RC oscillator.
Table 13-1. Reduced Crystal Table (MHz) OSCSEL = 0
3.0
6.0
18.432
Boot on DBGU
Yes
Yes
Yes
Boot on USB
Yes
Yes
Yes
Other
Yes
No
Note: Any other crystal can be used but it prevents using the USB.
b. If Internal RC Oscillator is used (OSCSEL = 0) and Main Oscillator is bypassed, Table 13-2 defines
the frequencies supported by the Boot Program when bypassing main oscillator.
Table 13-2. Input Frequencies Supported by Software Auto-detection (MHz) OSCSEL = 0
1.0
2.0
6.0
12.0
25.0
50.0
Other
Boot on DBGU
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Boot on USB
Yes
Yes
Yes
Yes
Yes
Yes
No
Note: Any other input frequency can be used but it prevents using the USB.
c. If an external 32768 Hz Oscillator is used (OSCSEL = 1), Table 13-3 defines the crystals supported
by the Boot Program.
Table 13-3.
3.0
4.433619
6.144
7.864320
12.0
16.0
Large Crystal Table (MHz) OSCSEL = 1
3.2768
3.6864
4.9152
5.0
6.4
6.5536
8.0
9.8304
12.288
13.56
16.367667
17.734470
3.84
5.24288
7.159090
10.0
14.31818
18.432
4.0
6.0
7.3728
11.05920
14.7456
20.0
Note: Booting either on USB or on DBGU is possible with any of these crystals.
SAM9260 [DATASHEET] 77
6221K–ATARM–15-Oct-12