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March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
Chapter 7:
Exceptions and Interrupts
R
Data-Storage Interrupt (0x0300)
Interrupt Classification
•
Noncritical—return using the
rfi
instruction.
•
Synchronous.
•
Precise.
Description
Data-storage exceptions are associated with the execution of an instruction that accesses
memory, including certain cache-control instructions. A data-storage exception occurs
when a data access fails for any of the following reasons:
•
An access is made to an address with
no-access-allowed
zone protection (the
corresponding zone-field value is 0b00). Any load, store,
dcbf
,
dcbst
,
dcbz
, or
icbi
instruction can cause an exception for this reason. No-access-allowed zone protection
is possible only in user mode with data virtual-mode enabled (MSR[DR]
=
1).
•
A store is made to a
read-only
address. Read-only addresses can only be specified
when data virtual-mode is enabled (MSR[DR]
=
1). Read-only addresses have the
write-enable bit (TLBLO[WR]) in the corresponding TLB entry cleared to zero. The
cause of this exception further depends on the privilege mode:
-
In user mode, any store or
dcbz
instruction can cause an exception for this reason.
No zone-protection override can be specified (the corresponding zone-field value
is
not
equal to 0b11).
-
In privileged mode, any store,
dcbi
,
dcbz
, or
dccci
instruction can cause an
exception for this reason. No zone-protection override can be specified (the
corresponding zone-field value is
not
equal to 0b10 or 0b11).
•
A store is made to an address with the corresponding U0 storage attribute set to 1 and
U0 exceptions are enabled (CCR0[U0XE]
=
1). In real mode, the U0 storage attribute is
specified by the SU0R register. In virtual mode, the U0 storage attribute is specified by
the TLB entry (TLBHI[U0]) used to translate the address. The instructions that can
cause an exception for this reason are:
-
In user mode, any store or
dcbz
instruction.
-
In privileged mode, any store,
dcbi
,
dcbz
, or
dccci
instruction.
System software can use this exception condition to implement real-mode write
protection.
Software cannot disable data-storage interrupts.
Affected Registers
Register
Value After Interrupt
SRR0
Loaded with the effective address of the instruction that caused the data-storage
exception.
SRR1
Loaded with a copy of the MSR at the point the interrupt occurs.
SRR2
Not used.
SRR3