AT91SAM9G46B-CU 查看數據表（PDF） - Atmel Corporation

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AT91SAM9G46B-CU

SMART ARM-based Embedded MPU

Atmel Corporation 

10.4.2 Valid Code Detection

There are two kinds of valid code detection. Depending on the NVM bootloader, either one or both of them is used.

10.4.2.1 ARM Exception Vectors Check

The NVM bootloader program reads and analyzes the first 28 bytes corresponding to the first seven ARM

exception vectors. Except for the sixth vector, these bytes must implement the ARM instructions for either branch

or load PC with PC relative addressing.

Figure 10-4. LDR Opcode

31

28 27

24 23

20 19

16 15

12 11

0

1 1 1 0 0 1 I PU 1W0

Rn

Rd

O set

Figure 10-5. B Opcode

31

28 27

24 23

0

11101010

O set (24 bits)

Unconditional instruction: 0xE for bits 31 to 28

Load PC with PC relative addressing instruction:

̶ Rn = Rd = PC = 0xF

̶ I==0 (12-bit immediate value)

̶ P==1 (pre-indexed)

̶ U offset added (U==1) or subtracted (U==0)

̶ W==1

The sixth vector, at offset 0x14, contains the size of the image to download. The user must replace this vector with

his/her own vector. This information is described below.

Figure 10-6. Structure of the ARM Vector 6

31

0

Size of the code to download in bytes

The value has to be smaller than 60 Kbytes. 60 Kbytes is the maximum size for a valid code. This size is the

internal SRAM size minus the stack size used by the ROM Code at the end of the internal SRAM.

Example

An example of valid vectors follows:

00

ea000006

04

eafffffe

08

ea00002f

0c

eafffffe

10

eafffffe

14

00001234

18

eafffffe

B0x20

B0x04

B_main

B0x0c

B0x10

B0x14 <- Code size = 4660 bytes <

60 Kbytes

B0x18

10.4.2.2 boot.bin file check

The NVM bootloader program looks for a boot.bin file in the root directory of a FAT12/16/32 formatted NVM Flash.

64 SAM9G46 Series [DATASHEET]

Atmel-11028G-ATARM-SAM9G46-Datasheet_08-Dec-15

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