AT91SAM9G20 datasheet(78/832 Pages) ATMEL

78 / 832 page

6384D–ATARM–04-May-09

AT91SAM9G20 Preliminary

Figure 13-5. Structure of the ARM Vector 6

13.4.2.1

Example

An example of valid vectors follows:

ea000006

0x20

eafffffe

0x04

ea00002f

_main

eafffffe

0x0c

eafffffe

0x10

00001234

0x14

<- Code size = 4660 bytes

eafffffe

0x18

The size of the image to load into SRAM is contained in the location of the sixth ARM vector.

Thus the user must replace this vector by the correct size of his/her application.

13.5

Serial Flash Boot

The Serial Flash boot looks for a valid application in the SPI Serial Flash memory.

SPI0 is configured in master mode to generate a SPCK at 8 MHz. Serial Flash shall be con-

nected to NPCS0 or NPCS1.

The Serial Flash boot reads the Serial Flash status register (Instruction code 0x05). The Serial

Flash is considered as ready if bit 0 of the returned status register is cleared.

If no Serial Flash is connected or if it does not answer, Serial Flash boot exits after 1000

attempts.

If the Serial Flash is ready, Serial Flash boot reads the first 8 words into SRAM (Instruction code

“Continuos read array” 0x0b) and checks if it corresponds to valid exception vectors according to

the Valid Image detection algorithm.

If a valid application is found, this application is loaded into internal SRAM and executed by

branching at address 0x0000_0000 after remap. This application may be the application code or

a second-level bootloader.

Size of the code to download in bytes

AT91SAM9G20 Datasheet(PDF) 78 Page - ATMEL Corporation