8.2.1 Boot mode pin settings
The device has four boot modes (one is reserved for Freescale use). Boot mode is
selected based on the binary value stored in the internal BOOT_MODE register.

BOOT_MODE is initialized by sampling the BOOT_MODE0 and BOOT_MODE1
inputs on the rising edge of POR_B. After these inputs are sampled, their subsequent
state does not affect the contents of the BOOT_MODE internal register. The state of the
internal BOOT_MODE register may be read from the BMOD[1:0] field of the SRC Boot
Mode Register (SRC_SBMR2). The available boot modes are: Boot From Fuses, serial
boot via USB, and Internal Boot. See the table below for settings.

Table 8-1. Boot MODE Pin Settings

BOOT_MODE[1:0]	Boot Type
00	Boot From Fuses
01	Serial Downloader
10	Internal Boot
11	Reserved

…

8.2.3 Boot From Fuses Mode (BOOT_MODE[1:0] = 00b)
A value of 00b in the BOOT_MODE[1:0] register selects the Boot From Fuses mode.

This mode is similar to the Internal Boot mode described in Internal Boot Mode
(BOOT_MODE[1:0] = 0b10)with one difference. In this mode the GPIO boot override
pins are ignored. The boot ROM code uses the boot eFUSE settings only. This mode also
supports a secure boot using HAB.

If set to Boot From Fuses, the boot flow is controlled by the BT_FUSE_SEL eFUSE
value. If BT_FUSE_SEL = 0, indicating that the boot device (for example, Flash, SD/
MMC) has not yet been programmed, the boot flow jumps directly to the Serial
Downloader. If BT_FUSE_SEL = 1, the normal boot flow is followed, where the ROM
attempts to boot from the selected boot device.

The first time a board is used, the default eFUSEs may be configured incorrectly for the
hardware on the platform. In such a case, the Boot ROM code may try to boot from a
device that does not exist. This may cause an electrical/logic violation on some pads.
Using Boot From Fuses mode addresses this problem.

Setting BT_FUSE_SEL=0 forces the ROM code to jump directly to the Serial
Downloader. This allows a bootloader to be downloaded which can then provision the
boot device with a Program Image and blow the BT_FUSE_SEL and the other boot
configuration eFUSEs. After reset, the Boot ROM code determines that BT_FUSE_SEL
is blown (BT_FUSE_SEL = 1) and the ROM code performs internal boot according to
the new eFUSE settings. This allows a user to set BOOT_MODE[1:0]=00b on a
production device and burn fuses on the same device (by forcing entry to the Serial
Downloader), without changing the value of BOOT_MODE[1:0] or pullups/pulldowns
on the BOOT_MODE pins.