March 2002 Release
621
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
Alphabetical Instruction Listing
R
dcread
Data Cache Read
Description
This is a privileged instruction.
An effective address (EA) is calculated by adding an index to a base address, which are
formed as follows:
•
The contents of register
r
B are used as the index.
•
If the
r
A field is 0, the base address is 0.
•
If the
r
A field is not 0, the contents of register
r
A are used as the base address.
This instruction can be used as a data-cache debugging aid. It is used to read information
for a specific data cacheline. The cache information is loaded in register
r
D.
EA
19:26
is used to specify a congruence class within the data cache. CCR0[CWS] is used to
select one of the two cachelines within the congruence class. If CCR0[CWS]
=
0, the line in
way A is selected. If CCR0[CWS]
=
1, the line in way B is selected.
If CCR0[CIS]
=
0, the information read is a word of data from the selected cacheline. EA
27
:
29
is used as an index to select the word from the 32-byte line. If CCR0[CIS]
=
1, the
information read is the tag associated with the selected cacheline.
Following execution of this instruction,
r
D contains the following:
dcread
r
D,
r
A,
r
B
X Instruction Form
31
r
D
r
A
r
B
486
0
0
6
1
1
1
6
2
1
3
1
Bit
Name
Function
Description
0:18
INFO
Data-Cache Information
CCR0[CIS]
=
0—Data word.
CCR0[CIS]
=
1—Data tag.
Contains either the cache-line tag or a single data word from the
cacheline. If a data word is loaded it is specified using effective-
address bits EA
27:29
. CCR0[CIS] controls the type of information
loaded into this field.
19:25
Reserved
26
D
Dirty
0—Cacheline is not dirty.
1—Cacheline is dirty.
Contains a copy of the cache-line dirty bit indicating whether or not
the line contains modified data.
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