Byte Swapping
The V5C has Byte Swapping implemented in hardware. This allows for proper
data transfer between the PCI and VME busses. The hardware implementation
is much faster than a software implementation since no extra processor time is
devoted to this task. Supported modes are: No swapping (M32), 32 bit
swapping (I32), and 16 bit swapping (I16). Note that byte swapping is not
applied to status ID’s associated with interrupt processing.
M32 allows data to transfer with no swapping of the bytes. All address and data
modes are supported with M32 since there is no swapping of bytes. M32 is the
default setting in the BIOS setup.
I32 allows conversion of big-endian to little-endian on a 32-bit transfer. Sup-
ported address modes are A16, A24, and A32. Supported data mode is D32. As
can be seen from the diagram on a four-byte transfer, bytes 0 and 3 are
swapped, and bytes 1 and 2 are swapped.
Byte Swapping
7-1
Byte Swapping Modes
Mode M32
C H A P T E R 7
Byte Swapping
Mode I32
Byte Swapping Modes
M32
I32
I16
Valid
Invalid
Invalid
Valid
Invalid
Valid
Valid
Valid
Invalid
Type of VMEbus Access
Byte
Word
Long Word
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