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March 2002 Release
555
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
R
Occasionally, it is desirable to cause a DVC event during an access to
unaligned data. Software can use both DVC1 and DVC2 to (and the
corresponding DAC
n
registers) to detect accesses to either portion of the
misaligned data. However, misaligned accesses can result in the generation of
two effective addresses that are accessed separately by the processor. If the
first address causes a DVC event, that event is recorded before completing
access to the second address. If an interrupt occurs as a result of the DVC
event, the second access is lost. This can result in a corrupted register and/or
memory value.
DVC read and write events are enabled by initializing the DAC comparison
and the D
n
R and D
n
W control bits in DBCR1. When a DVC event occurs,
DBSR status bits are set to reflect the event. Read and write DVC events are
recorded independently using the DR
n
and DW
n
status bits.
summarizes how the status bits are used by DVC events.
Status bits can be set by either DAC events or DVC events. However, a DAC
event can occur only when DVC events are disabled. DAC matches do not set
the status bits if DVC events are enabled but fail to occur. After a DAC or DVC
event is recorded by a debugger, the corresponding status bits should be
cleared to prevent ambiguity when recording future debug events.
Table 9-11:
Examples of Using DVC1 Controls
Data Value
DVC1 Value
DV1BE
DV1M
DVC1 Match
0xABCD_FFFF
0xABCD_0123
0b0111
01 (AND)
No
10 (OR)
Yes
11 (AND–OR)
No
0b1000
01 (AND)
Yes
10 (OR)
Yes
11 (AND–OR)
No
0b1100
01 (AND)
Yes
10 (OR)
Yes
11 (AND–OR)
Yes
0b1111
01 (AND)
No
10 (OR)
Yes
11 (AND–OR)
Yes
Table 9-12:
DVC Event Status
DAC Enable Bit
(DBCR1)
Type of Access
Checked
Registers Used
DVC Status Bit
(DBSR)
D1R
Load (Read)
DAC1
DVC1
DR1
D1W
Store (Write)
DW1
D2R
Load (Read)
DAC2
DVC2
DR2
D2W
Store (Write)
DW2
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