196
SAM4CP [DATASHEET]
43051E–ATPL–08/14
12.9.1.5 Application Interrupt and Reset Control Register
Name:
SCB_AIRCR
Access:
Read/Write
The SCB_AIRCR provides priority grouping control for the exception model, endian status for data accesses, and reset control of
the system. To write to this register, write 0x5FA to the VECTKEY field, otherwise the processor ignores the write.
VECTKEYSTAT: Register Key
Read:
Reads as 0xFA05.
VECTKEY: Register Key
Write:
Writes 0x5FA to VECTKEY, otherwise the write is ignored.
ENDIANNESS: Data Endianness
0: Little-endian.
1: Big-endian.
PRIGROUP: Interrupt Priority Grouping
This field determines the split of group priority from subpriority. It shows the position of the binary point that splits the PRI_
n
fields
in the Interrupt Priority Registers into separate
group priority
and
subpriority
fields. The table below shows how the PRIGROUP
value controls this split:
Note:
Determining preemption of an exception uses only the group priority field.
1. PRI_n[7:0] field showing the binary point. x denotes a group priority field bit, and y denotes a subpriority field bit.
31
30
29
28
VECTKEYSTAT/VECTKEY
27
26
25
24
23
22
21
20
VECTKEYSTAT/VECTKEY
19
18
17
16
15
14
13
12
11
10
9
8
ENDIANNESS
–
PRIGROUP
7
6
5
4
3
2
1
0
–
SYSRESETREQ VECTCLRACTIVE
VECTRESET
Interrupt Priority Level Value, PRI_
N
[7:0]
Binary Point
(1)
Group Priority Bits
bxxxxxxx.y
[7:1]
bxxxxxx.yy
[7:2]
bxxxxx.yyy
[7:3]
bxxxx.yyyy
[7:4]
bxxx.yyyyy
[7:5]
bxx.yyyyyy
[7:6]
bx.yyyyyyy
[7]
b.yyyyyyy
None
Number of
PRIGROUP
0b000
0b001
0b010
0b011
0b100
0b101
0b110
0b111
Subpriority Bits
None
[4:0]
[4:0]
[4:0]
[4:0]
[5:0]
[6:0]
[7:0]
Group Priorities
128
64
32
16
8
4
2
1
Subpriorities
2
4
8
16
32
64
128
256