Configuration
3-8
Copyright © ARM Limited 1997, 1998, 2000. All rights reserved.
ARM DDI 0192A
3.3.5
Register 4, reserved
Register 4 is reserved. Reading CP15 register 4 is unpredictable. Writing CP15 register
4 is unpredictable. This is shown in Figure 3-8.
Figure 3-8 Register 4
3.3.6
Register 5, fault status register
Reading CP15 register 5 returns the value of the Fault Status Register (FSR). The FSR
contains the source of the last data fault.
Note
Only the bottom 9 bits are returned. The upper 23 bits are unpredictable.
The FSR indicates the domain and type of access being attempted when an abort
occurred:
Bit 8
This is always read as zero. Bit 8 is ignored on writes.
Bits [7:4]
These specify which of the 16 domains (D15-D0) was being
accessed when a fault occurred.
Bits [3:1]
Theses indicate the type of access being attempted.
The encoding of these bits is shown in Fault address and fault status registers on
page 6-19. The FSR is only updated for data faults, not for prefetch faults.
Writing CP15 register 5 sets the FSR to the value of the data written. This is useful when
a debugger has to restore the value of the FSR. The upper 24 bits written should be zero.
The CRm and opcode_2 fields should be zero when reading or writing CP15 register 5.
Register 5 is shown in Figure 3-9.
Figure 3-9 Register 5
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
UNP
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
UNP/SBZ
0
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