4.3.5. Application Interrupt and Reset Control Register

The AIRCR provides priority grouping control for the exception model, endian status for data accesses, and reset control of the system. See the register summary in Table 4.12 and Table 4.17 for its attributes.

To write to this register, you must write 0x5FA to the VECTKEY field, otherwise the processor ignores the write.

The bit assignments are:

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Table 4.17. AIRCR bit assignments

BitsNameTypeFunction
[31:16]

Read: VECTKEYSTAT

Write: VECTKEY

RW

Register key:

Reads as 0xFA05.

On writes, write 0x5FA to VECTKEY, otherwise the write is ignored.

[15]ENDIANNESSRO

Data endianness bit setting is implementation defined:

0

Little-endian.

1

Big-endian.

[14:11]--Reserved.
[10:8]PRIGROUPRW

Interrupt priority grouping field. This field determines the split of group priority from subpriority, see Binary point.

[7:3]- -Reserved.
[2]SYSRESETREQWO

System reset request bit setting is implementation defined:

0

No system reset request.

1

Asserts a signal to request a system reset.

This is intended to force a large system reset of all major components except for debug.

This bit reads as 0.

See your vendor documentation for more information about the use of this signal in your implementation.

[1]VECTCLRACTIVEWOReserved for Debug use. This bit reads as 0. When writing to the register you must write 0 to this bit, otherwise behavior is Unpredictable.
[0]VECTRESETWOReserved for Debug use. This bit reads as 0. When writing to the register you must write 0 to this bit, otherwise behavior is Unpredictable.

Binary point

The PRIGROUP field indicates the position of the binary point that splits the PRI_n fields in the Interrupt Priority Registers into separate group priority and subpriority fields. Table 4.18 shows how the PRIGROUP value controls this split. Implementations having PRI_n fields of less than 8 bits treat the least-significant bits as zero.

Table 4.18. Priority grouping

 Interrupt priority level value, PRI_N[7:0]Number of
PRIGROUPBinary point[a]Group priority bitsSubpriority bitsGroup priorities[b]Subpriorities[b]
0b000[c]bxxxxxxx.y[7:1][0]1282
0b001[c]bxxxxxx.yy[7:2][1:0]644
0b010[c]bxxxxx.yyy[7:3][2:0]328
0b011[c]bxxxx.yyyy[7:4][3:0]1616
0b100bxxx.yyyyy[7:5][4:0]832
0b101bxx.yyyyyy[7:6][5:0]464
0b110bx.yyyyyyy[7][6:0]2128
0b111b.yyyyyyyyNone[7:0]1256

[a] PRI_n[7:0] field showing the binary point. x denotes a group priority field bit, and y denotes a subpriority field bit.

[b] Implementation defined.

[c] Optional.


Note

Determining preemption of an exception uses only the group priority field, see Interrupt priority grouping.

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