RM0319 datasheet(42/368 Pages) STMICROELECTRONICS

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BootROM

RM0319

42/368

Doc ID 022640 Rev 3

5.6.3

BootROM Bypass

BootROM bypass mode uses the serial NOR device in XIP (execute in place) mode. The

image header is authenticated and the code directly jumps to an address pointed to by the

image load address (ih_load) found in the image header. When using BootROM bypass

mode, no validation or authentication is performed on the image data, it is the sole

responsibility of the user to ensure that the image being executed comes from a trusted

source

Header authentication is performed in 3 steps:

The value of bits 3:0 in the Boot_Strap_Reg (address 0xB3000000) is compared with

0xB

ih_magic is compared with 0x27051956

ih_hcrc is compared with the calculated CRC of the header

If the authentication is successful, then BootROM jumps to address ih_load

If authentication fails, or any other error occurs, BootROM shifts to USB boot.

Figure 10.

Serial NOR Flash boot & BootROM bypass

5.6.4

NAND Flash boot

To detect NAND devices, initialize the FSMC controller with the relaxed timing values:

–

Thiz

= 0x01

–

Thold = 0x04

–

Twait = 0x06

–

Tset

= 0x00

BootROM

Bypass mode

authenticated?

bypass

Passed

YES

Jump to

ih_load

USB boot

Copy X

Loader from Flash to shadow memory

Authenticate X

Loader?

Failed

Jump (at ih_load) to X

Loader in shadow memory

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