
MOTOROLA
Chapter 6. Memory Management
6-15
MMU Features
exception by setting the appropriate bits in the DSISR or SRR1 and branching to the ISI or
DSI exception handler. Refer to Section 6.5.2, “Implementation-Specific Table Search
Operation,” for more information and examples of this exception software. The remainder
of this chapter assumes that the table search software emulates this exception and refers to
this condition as an exception.
The translation exception conditions defined by the OEA for 32-bit implementations cause
either the ISI or the DSI exception to be taken as shown in Table 6-3.
In addition to the translation exceptions, there are other MMU-related conditions (some of
them defined as implementation-specific and, therefore, not required by the architecture)
that can cause an exception to occur in the G2 core. These exception conditions map to the
processor exception as shown in Table 6-4. For example, the G2 core also defines three
exception conditions to support software table searching. The only exception conditions
that occur when MSR[DR] = 0, are the conditions that cause the alignment exception for
Table 6-3. Translation Exception Conditions
Condition
Description
Exception
Page fault (no PTE found)
No matching PTE found in page tables (and no
matching BAT array entry)
I access: ISI exception
1
SRR1[1] = 1
1
The G2 core hardware does not vector to these exceptions automatically. It is assumed that the software that
performs the table search operation vectors to these exceptions and sets the appropriate bits when a page fault
condition occurs.
2
The table search software can also vector to these exception conditions.
D access: DSI exception
1
DSISR[1] =1
Block protection violation
Conditions described for block in “Block Memory
Protection” in Chapter 7, “Memory Management,”
in the
Programming Environments Manual.
“
I access: ISI exception
SRR1[4] = 1
D access: DSI exception
DSISR[4] =1
Page protection violation
Conditions described for page in “Page Memory
Protection” in Chapter 7, “Memory Management,”
in the
Programming Environments Manual.
I access: ISI exception
2
SRR1[4] = 1
D access: DSI exception
2
DSISR[4] =1
No-execute protection violation
Attempt to fetch instruction when SR[N] = 1
ISI exception
SRR1[3] = 1
Instruction fetch from direct-store
segment
Attempt to fetch instruction when SR[T] = 1
ISI exception
SRR1[3] =1
Data access to direct-store segment
(including floating-point accesses)
Note
: This is a G2 core-specific
condition
Attempt to perform load or store (including
floating-point load or store) when SR[T] = 1
DSI exception
DSISR[5] =1
Instruction fetch from guarded
memory with MSR[IR] = 1
Attempt to fetch instruction when MSR[IR] = 1
and either matching xBAT[G] = 1, or no matching
BAT entry and PTE[G] = 1.
ISI exception
SRR1[3] =1
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.