Digi NS9215 - Manual (Page 92)

W O R K I N G W I T H T H E C P U
R4 register
92 Hardware Reference NS9215
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R 4 r e g i s t e r
Accessing (reading or writing) this register causes UNPREDICTABLE behavior.
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R 5 : F a u l t S t a t u s r e g i s t e r s
Register R5 accesses the Fault Status registers (FSRs). The Fault Status registers
contain the source of the last instruction or data fault. The instruction-side FSR is
intended for debug purposes only.
The FSR is updated for alignment faults and for external aborts that occur while the
MMU is disabled. The FSR accessed is determined by the
opcode_2 value:
See "MemoryManagement Unit (MMU)," beginning on page 105, for the fault type
encoding.
Access
instructions
Access the FSRs using these instructions:
MRC p15, 0, Rd, c5, c0, 0; read DFSR
MCR p15, 0, Rd, c5, c0, 0; write DFSR
MRC p15, 0, Rd, c5, c0, 1; read IFSR
MCR p15, 0, Rd, c5, c0, 1; write IFSR
Register format
Register bits
opcode_2=0 Data Fault Status register (DFSR)
opcode_2=1 Instruction Fault Status register (IFSR)
31 0 9 8 7 4 3
0 UNP/SBZ Domain Status
Bits Description
[31:9] UNPREDICTABLE/SHOULD BE ZERO
[8] Always reads as zero. Writes are ignored.
[7:4] Specifies which of the 16 domains (D15–D0) was being accessed when a data fault
occurred.
[3:0] Type of fault generated. (See "MemoryManagement Unit (MMU)," beginning on page
105.)