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Functional Description
2.7 SYM53C895 Modes
This section provides information about:
PCI Cache Mode
Big and Little Endian Modes
Loopback Mode
2.7.1 PCI Cache Mode
The SYM53C895 supports the PCI specication for an 8-bit Cache Line
Size register located in PCI conguration space. The Cache Line Size
register provides the ability to sense and react to nonaligned addresses
corresponding to cache line boundaries. In conjunction with the Cache
Line Size register, the PCI commands Read Line, Read Multiple, and
Write and Invalidate are each software enabled or disabled to allow the
user full exibility in using these commands. For more information on PCI
cache mode operations, refer to
Chapter 3, “PCI Functional Description.”
2.7.2 Big and Little Endian Modes
The SYM53C895 supports both big and little endian byte ordering
through pin selection. In big endian mode, the rst byte of an aligned
SCSI to PCI transfer is routed to lane three and successive transfers are
routed to descending lanes. This mode of operation also applies to data
transfers over the add-in ROM interface. The byte of data accessed at
memory location 0x0000 is routed to lane three, and the data at location
0x0003 is routed to byte lane 0. In little endian mode, the rst byte of an
aligned SCSI to PCI transfer is routed to lane zero and successive
transfers are routed to ascending lanes. This mode of operation also
applies to the add-in ROM interface. The byte of data accessed at
memory location 0x0000 is routed to lane zero, and the data at memory
location 0x0003 is routed to byte lane 3.
The BIG_LIT pin gives the SYM53C895 the exibility of operating with
either big or little endian byte orientation. Internally, in either mode, the
actual byte lanes of the DMA FIFO and registers are not modied. The
SYM53C895 supports slave accesses in big or little endian mode.