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MOTOROLA M68040 USER'S MANUAL 3- 11
CREATE ATC ENTRY
WITH R-BIT CLEAR
FETCH DESCRIPTOR &
UPDATE HISTORY AND STATUS
FETCH DESCRIPTOR
AT PA = TA + (INDEX*4)
FETCH DESCRIPTOR AT
PA = DESCRIPTOR ADDRESS
WP = WP V W
OR 'INDIRECT'
EXECUTE
WRITE ACCESS
U 1, M 1
EXECUTE
LOCKED
RMW ACCESS
U 1
U = 1 &
U = 0 &
SCHEDULE
WRITE ACCESS 
U 1
(SEE NOTE)
WP = WP V W
IF SCHEDULED, EXECUTE
WRITE ACCESS (U 1) FOR
PREVIOUS DESCRIPTOR
CREATE ATC ENTRY
WITH R-BIT CLEAR
WP – ACCUMULATED WRITE-
PROTECTION STATUS
V – LOGICAL "OR" OPERATOR
– ASSIGNMENT OPERATOR
DUE TO ACCESS PIPELINING, A POINTER
DESCRIPTOR WRITE ACCESS TO UPDATE
THE U-BIT OCCURS AFTER THE READ OF
THE NEXT LEVEL DESCRIPTOR.
NOTE :
ABBREVIATIONS:
RETURN
RETURN
RETURN
RETURN EXIT TABLE SEARCH
EXIT TABLE SEARCH
TYPE = 'PAGE' OR 'POINTER'
OTHERWISE
TYPE = 'PAGE'
'INVALID'
'RESIDENT''RESIDENT'
U = 1
U = 0
'INVALID'
TYPE =
'POINTER'
READ ACCESS
U = 0 (WP = 1 OR M = 1) (WP = 1 OR M = 1)
WP = 0 & M = 0
U = 1
WRITE ACCESS
OTHERWISE
TYPE = 'INDIRECT'
(INDEX = RI, PI, OR PGI)
(SEE NOTE)
NORMAL TERMINATION
OF ALL BUS TRANSFERS
NORMAL TERMINATION
OF ALL BUS TRANSFERS
OR 'INDIRECT'
Figure 3-10. Detailed Flowchart of Descriptor Fetch Operation
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