Digi NS9215 - Manual (Page 120)

W O R K I N G W I T H T H E C P U
MMU faults and CPU aborts
120 Hardware Reference NS9215
register. If an access violation simultaneously generates more than one source of
abort, the aborts are encoded in the priority shown in the priority encoding table.
The Fault Address register is not updated by faults caused by instruction prefetches.
Priority encoding
table
Notes:
Alignment faults can write either 0b0001 or 0b0011 into Fault Status register [3:0] .
Invalid values can occur in the status bit encoding for domain faults. This
happens when the fault is raised before a valid domain field has been read
from a page table description.
Aborts masked by a higher priority abort can be regenerated by fixing the
cause of the higher priority abort, and repeating the access.
Alignment faults are not possible for instruction fetches.
The Instruction Fault Status register can be updated for instruction prefetch
operations
( MCR p15,0,Rd,c7,c13,1 )
.
Fault Address
register (FAR)
For load and store instructions that can involve the transfer of more than one word
(
LDM/STM, STRD, and STC/LDC ), the value written into the Fault Address register
depends on the type of access and, for external aborts, on whether the access
crosses a 1 KB boundary.
FAR values for
multi-word
transfers
Priority Source Size Status Domain
Highest Alignment --- 0b00x1 Invalid
External abort on transmission First level
Second level 0b1100
0b1110
Invalid
Valid
Translation Section page 0b0101
0b0111
Invalid
Valid
Domain Section page 0b1001
0b1011
Valid
Valid
Permission Section page 0b1101
0b1111
Valid
Valid
Lowest External abort Section page 0b1000
0b1010
Valid
Valid
Domain Fault Address register
Alignment MVA of first aborted address in transfer
External abort on translation MVA of first aborted address in transfer
Translation MVA of first aborted address in transfer