at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 75

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

13.4
13.4.1
13.4.2
6384B–ATARM–15-Dec-08
Valid Image Detection
Valid ARM exception vectors
Structure of ARM Vector 6
Figure 13-2. Remap Action after Download Completion
The DataFlash Boot software looks for a valid application by analyzing the first 28 bytes corre-
sponding to the ARM exception vectors. These bytes must implement ARM instructions for
either branch or load PC with PC relative addressing.
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 (see
Figure 13-3. LDR Opcode
Figure 13-4. B Opcode
Unconditional instruction: 0xE for bits 31 to 28
Load PC with PC relative addressing instruction:
The ARM exception vector 6 is used to store information needed by the DataFlash boot pro-
gram. This information is described below.
31
31
1
1
1
1
– Rn = Rd = PC = 0xF
– I==0
– P==1
– U offset added (U==1) or subtracted (U==0)
– W==1
1
1
28 27
28 27
0
0
0x0000_0000
0x0020_0000
0
1
1
0
1
I
24 23
24 23
P
0
U
Internal
Internal
SRAM
ROM
0
W 1
20 19
AT91SAM9G20 Preliminary
Rn
REMAP
“Structure of ARM Vector 6” on page
16 15
Offset (24 bits)
Rd
Internal
Internal
SRAM
ROM
12 11
0x0000_0000
0x0010_0000
75).
0
0
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