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System bootEdit
The boot process begins at Power On Reset (POR) where the hardware reset logic forces the ARM core to begin execution starting from the on-chip boot ROM. The boot ROM:
- determines whether the boot is secure or non-secure
- performs some initialization of the system and clean-ups
- reads the mode pins to determine the primary boot device
- once it is satisfied, it executes the boot code
Boot optionsEdit
Many options are available related to system boot. They are selected by the BOOT_MODE_x signals as follow:
| BOOT_MODE_2 | BOOT_MODE_1 | BOOT_MODE_0 | BOOT peripheral |
|---|---|---|---|
| 0 | 0 | 0 | Boot From Internal Fuses |
| 0 | 0 | 1 | USB Serial Download |
| 0 | 1 | 0 | USDHC3 (eMMC boot only, SD3 8-bit) |
| 0 | 1 | 1 | USDHC2 (SD boot only, SD2) |
| 1 | 0 | 0 | NAND 8-bit single device 256 page |
| 1 | 0 | 1 | NAND 8-bit single device 512 page |
| 1 | 1 | 0 | QSPI 3B Read |
When the signals are left floating the primary boot device is set by default to eMMC on SD3.
The BOOT_MODE_x signals are latched when processor reset is released.
In any case, boot process is managed by on-chip boot ROM code that is described in detail in processor's Reference Manual.