UM0851 datasheet(13/245 Pages) STMICROELECTRONICS

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UM0851

Boot loader overview

Doc ID 16604 Rev 2

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Boot loader overview

The SPEAr boot process is divided into four different stages. On power-on the BootROM

hard coded in the silicon (eROM) starts (first stage). Its role is to locate XLoader and

transfer the control to it. The BootROM is embedded in the silicon and is not part of the LSP.

The following sections describe the features offered by the components which are not

embedded in the silicon (XLoader and U-Boot) because they are usually board dependent

and need to be customized by the user. These components are part of LSP v2.3.

For a detailed description, please refer to the corresponding SPEAr datasheet and user

manual.

Figure 1.

SPEAr booting stages

1.1

XLoader

XLoader is a small firmware loaded during the second stage of the boot phase by the

BootROM.

The main steps performed by XLoader in LSP v2.3 are:

●

Initializing the DDR and PLLs at 333 MHz

●

Passing of board information (DDR size etc.) to U-Boot

●

Loading the U-Boot from NAND, NOR depending on boot type selection and

transferring the control to it.

The XLoader coming with the LSP v2.3 is licensed under GPLv2 and distributed in full

source code. This distributed XLoader version runs on the SPEAr hardware development

kits. You have to customize Xloader to run it on a different PCB, especially the MPMC

Reset

ARM

High vectors

eSRAM

Shadow

memory

BootROM

NAND/NOR

DDR

Embedded in SPEAr

Part of LSP

BootROM

X-Loader

U-Boot

Linux/OS

eROM

FFFF0000h

D2800000h

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