AT91SAM9G20 datasheet(73/832 Pages) ATMEL

73 / 832 page

6384D–ATARM–04-May-09

AT91SAM9G20 Preliminary

13. AT91SAM9G20 Boot Program

13.1

Overview

The Boot Program integrates different programs that manage download and/or upload into the

different memories of the product.

First, it initializes the Debug Unit serial port (DBGU) and the USB High Speed Device Port.

The Boot program tries to detect SPI flash memories. The Serial Flash Boot program and Data-

Flash

® Boot program are executed. It looks for a sequence of seven valid ARM exception

vectors in a Serial Flash or DataFlash connected to the SPI. All these vectors must be B-branch

or LDR load register instructions except for the sixth vector. This vector is used to store the size

of the image to download.

If a valid sequence is found, code is downloaded into the internal SRAM. This is followed by a

remap and a jump to the first address of the SRAM.

If no valid ARM vector sequence is found, NAND Flash Boot program is then executed. The

NAND Flash Boot program looks for a sequence of seven valid ARM exception vectors. If such a

sequence is found, code is downloaded into the internal SRAM. This is followed by a remap and

a jump to the first address of the SRAM.

If no valid ARM exception vector is found, the SDCard Boot program is then executed. It looks

for a boot.bin file in the root directory of a FAT12/16/32 formatted SDCard. If such a file is found,

code is downloaded into the internal SRAM. This is followed by a remap and a jump to the first

address of the SRAM.

If the SDCard is not formatted or if boot.bin file is not found, TWI Boot program is then executed.

The TWI Boot program searches for a valid application in an EEPROM memory. If such a file is

found, code is downloaded into the internal SRAM. This is followed by a remap and a jump to

the first address of the SRAM.

If no validapplication is found, SAM-BA Boot is then executed. It waits for transactions either on

the USB device, or on the DBGU serial port.

13.2

Flow Diagram

The Boot Program implements the algorithm in Figure 13-1.

AT91SAM9G20 Datasheet(PDF) 73 Page - ATMEL Corporation