Xilinx Virtex-II Pro PPC405, User Manual

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March 2002 Release www.xilinx.com 551
Virtex-II Pro™ Platform FPGA Documentation 1-800-255-7778
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granularity. The following table shows the possible size-field values, the
address bits that are ignored during the comparison, and the resulting
granularity used in the comparison.
Table 9-8 shows an example of using the D1S size field. The table shows how
comparisons against the DAC address are modified using the size field. The
first four entries apply byte-granular comparisons and only one of the four
accesses produces a match. The second set of four entries apply a word-
granular comparison. Here, all four of the accesses produce a match.
The load-string and store-string instructions move bytes of data between
memory and registers. However, when these instructions are used to access
data PPC405 moves four bytes at a time by using word-aligned effective
addresses and an access size of one word. Bytes not required by the
instructions are discarded. Thus, it is not possible to produce a byte-granular
DAC match on every byte address referenced by a string instruction. In some
cases, software must use a word-size granularity to produce a DAC match on
a specific byte address.
DAC Address-Range Match
A DAC address-range match causes a debug event when the effective address
of the operand falls within a range specified by the DA12 register pair. DAC1
and DAC2 form the DA12 pair. DA12 range comparison is enabled by setting
DBCR1[DA12]
=
1. When DAC address-range comparison is enabled, DAC
exact-address comparison is disabled. The DBCR1[D1S, D2S] size bits are not
used by DAC address-range comparisons.
Read and write accesses can be checked independently. To check read
accesses, software sets the D1R and/or D2R bits in the DBCR1 register. Only
one of the two bits must be set to enable read checking for the entire range. If
Table 9-7: Effect of D1S/D2S Size-Field Encoding
Size-Field Encoding Address Bits Used Address Bits Ignored Granularity
00 0:31 — Byte
01 0:30 31 Halfword
10 0:29 30:31 Word
11 0:26 27:31 Cacheline
Table 9-8: Examples of Using the D1S Size Field
DAC Address
D1S Value
(Granularity)
Operand Address Access Size DAC Match
0x0002
00
(Byte)
0x0000 Byte No
0x0000 Word No
0x0002 Word Yes
0x0003 Byte No
0x0002
10
(Word)
0x0000 Byte Yes
0x0000 Word Yes
0x0002 Word Yes
0x0003 Byte Yes