
MOTOROLA
Chapter 5. Exceptions
5-25
Exception Definitions
DSI exceptions can occur for any of the following reasons:
The instruction is not supported for the type of memory addressed
Any access to a direct-store segment (SR[T] = 1)
The attempted access violates the memory protection defined by SR[Ks,Kp],
PTE[PP], or DBATn[PP].
Note that the OEA specifies an additional case that may cause a DSI exception—when an
effective address for a load, store, or cache operation cannot be translated by the TLBs. On
the G2 core, this condition causes a TLB miss exception instead. These scenarios are
common among all processors that implement the PowerPC architecture. The following
additional scenarios can cause a DSI exception in the G2 core:
A bus error indicates crossing from a direct-store segment to a memory segment
Table 5-14. DSI Exception—Register Settings
Register
Setting Description
SRR0
Set to the effective address of the instruction that caused the exception.
SRR1
0–15
16–31 Loaded with MSR[16–31]
Cleared
MSR
POW 0
TGPR 0
ILE
EE
PR
—
0
0
FP
ME
FE0
SE
BE
0
—
0
0
0
FE1
CE
IP
IR
DR
0
—
—
0
0
RI
LE
0
Set to value of ILE
DSISR
0
Set if a load or store instruction results in a direct-store error exception due to a load or store
instruction accesses a direct-store segment by setting a T bit.
Set by the data TLB miss exception handler if the translation of an attempted access is not
found in the primary hash table entry group (HTEG), or in the rehashed secondary HTEG, or in
the range of a DBAT register; otherwise cleared.
Cleared
Set if a memory access is not permitted by the page or BAT protection mechanism; otherwise
cleared.
Set if the
lwarx
or
stwcx.
instruction is attempted to direct-store space
Set for a store operation and cleared for a load operation
G2_LE core only. Set when a data address breakpoint exception when the data (bit 29) in the
DABR1 or DABR2 matches the next data access (load or store instruction) to complete in the
completion unit. The different breakpoints are enabled as follows:
Write breakpoints enabled when DABR[30] is set
Read breakpoints enabled when DABR[31] is set
Cleared
1
2–3
4
5
6
9
7–31
DAR
Set to the effective address of a memory element as described in the following list:
A byte in the first word accessed in the page that caused the DSI exception, for a byte, half word, or
word memory access.
A byte in the first word accessed in the BAT area that caused the DSI exception for a byte, half word,
or word access to a BAT area.
A byte in the block that caused the exception for
icbi
,
dcbz
,
dcbst
,
dcbf
,
or
dcbi
1
instructions.
The EA that causes a data breakpoint for the G2_LE core.
Any EA in the memory range addressed (for direct-store exceptions).
1
The
dcbi
instruction should never be used on the G2 core.
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