
8-24
M68040 USER’S MANUAL
MOTOROLA
8.4.6 Access Error Stack Frame (Format $7)
A 30-word access error stack frame is created for data and instruction access faults other
than instruction address errors. In addition to information about the current processor
status and the faulted access, the stack frame also contains pending write-backs that the
access error exception handler must complete. The following paragraphs describe in
detail the format for this frame and how the processor uses it when returning from
exception processing.
Stack Frames
Exception Types
Data or Instruction Access
Fault (ATC Fault or Bus
Error)
Stacked PC Points To
Next Instruction
SPECIAL STATUS WORD (SSW)
$00
WRITE-BACK 3 STATUS (WB3S)
$00
WRITE-BACK 1 STATUS (WB1S)
0
15
SP
+$02
+$12
+$14
ACCESS ERROR STACK FRAME
(30 WORDS)–FORMAT $7
FAULT ADDRESS (FA)
WRITE-BACK 3 ADDRESS (WB3A)
WRITE-BACK 3 DATA (WB3D)
WRITE-BACK 1 DATA/PUSH DATA LW0 (WB1D/PD0)
PUSH DATA LW 1 (PD1)
WRITE-BACK 2 ADDRESS (WB2A)
WRITE-BACK 2 DATA (WB2D)
WRITE-BACK 1 ADDRESS (WB1A)
PUSH DATA LW 2 (PD2)
PUSH DATA LW 3 (PD3)
+$18
+$1C
+$20
+$24
+$28
+$2C
+$30
+$34
+$38
STATUS REGISTER
PROGRAMCOUNTER
0 1 1 1
VECTOR OFFSET
EFFECTIVE ADDRESS (EA)
$00
WRITE-BACK 2 STATUS (WB2S)
+$10
+$0C
+$0E
+$08
+$0A
+$06
8.4.6.1 EFFECTIVE ADDRESS.
The effective address contains address information when
one of the continuation flags CM, CT, CU, or CP in the SSW is set.
8.4.6.2 SPECIAL STATUS WORD (SSW).
The SSW information indicates whether an
access to the instruction stream or the data stream (or both) caused the fault and contains
status information for the faulted access. Figure 8-7 illustrates the SSW format.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
CP
CU
CT
CM
MA
ATC
LK
RW
X
SIZE
TT
TM
Figure 8-7. Special Status Word Format