Burst Ordering During Data Transfers; Effect Of Alignment On Data Transfers - Motorola MPC8260 PowerQUICC II User Manual

Part III. The Hardware Interface
Table 8-4. Transfer Size Signal Encoding (Continued)
TBST TSIZ[0Ð3]
Negated 0 1 1 1
Negated 0 0 0 0
Negated 1 0 0 1
Negated 1 0 1 0
Asserted 0 0 1 0
Note that the basic coherency size of the bus is 32 bytes for the processor (cache-block
size). Data transfers that cross an aligned 32-byte boundary must present a new address
onto the bus at that boundary for proper snoop operation, or must operate as non-coherent
with respect to the MPC8260.

8.4.3.4 Burst Ordering During Data Transfers

During burst transfers, 32 bytes of data (one cache block) are transferred to or from the
cache. Burst write transfers are performed zero double-word-Þrst. However, because burst
reads are performed critical-double-word-Þrst, a burst-read transfer may not start with the
Þrst double word of the cache block and the cache-block-Þll operation may wrap around
the end of the cache block. Table 8-5 describes MPC8260 burst ordering.
Data Transfer
1st data beat
2nd data beat
3rd data beat
4th data beat
1
A[27Ð28] speciÞes the Þrst double word of the 32-byte block being transferred; any subsequent double words must
wrap-around the block. A[29Ð31] are always 0b000 for burst transfers by the MPC8260.
2
DWx represents the double word that would be addressed by A[27Ð28] = x if a nonburst transfer were performed.
Each data beat is terminated with an assertion of TA.

8.4.3.5 Effect of Alignment on Data Transfers

Table 8-6 lists the aligned transfers that can occur to and from the MPC8260. These are
transfers in which the data is aligned to an address that is an integer multiple of the size of
the data. For example, Table 8-6 shows that 1-byte data is always aligned; however, a 4-byte
word must reside at an address that is a multiple of 4 to be aligned.
In Figure 8-6, Table 8-8, and Table 8-9, OP0 is the most-signiÞcant byte of a word operand
and OP7 is the least-signiÞcant byte.
8-14
Transfer Size
7 Bytes Extended 7 bytes
8 Bytes Double-word (maximum data bus size)
16 Bytes Extended double double-word
24 Bytes Extended triple double-word
32 bytes Quad double-word (4 maximum data beats)
Table 8-5. Burst Ordering
Double-Word Starting Address:
1
A[27Ð28] = 00 A[27Ð28] = 01
2
DW0
DW1
DW2
DW3
MPC8260 PowerQUICC II UserÕs Manual
Comments
A[27Ð28] = 10
DW1 DW2
DW2 DW3
DW3 DW0
DW0 DW1
Source
SDMA (MPC8260 only)
Core and DMA
SDMA (MPC8260 only)
SDMA (MPC8260 only)
Core and DMA
A[27Ð28] = 11
DW3
DW0
DW1
DW2
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