2. PCI Interface
43
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
In order to program PowerSpan II to complete 4 byte reads on the PCI bus, both the MEM_IO bit and
the MODE bit must be set to 1 in the PCI
x
Target Image
x
Control register.
In order to perform a 4-byte read from the PCI bus to the processor (60x) bus, the following bits must
be programmed:
•
MEM_IO bit set to 1
•
MODE bit set to 1 or 0
•
END bit, in the
“PCI-1 Target Image x Control Register” on page 268
, must not be set to
little-endian mode (00). It can be set to PowerPC little-endian (01), or big-endian (10).
PowerSpan II prefetch behavior on the destination bus when claiming Memory reads on the originating
bus is controlled by the PCI Memory Read Alias (MRA) bit and the Prefetch Size (RD_AMT[2:0])
field in the
“PCI-1 Target Image x Control Register” on page 268
. If the MRA bit is set when
PowerSpan II claims a memory read, PowerSpan II prefetches the amount programmed into the
RD_AMT[2:0] field
—
up to 128 bytes.
The Memory Read Line command results in a prefetch of the value programmed into Cache Line
(CLINE) bit. When the MRA bit is cleared, the target image prefetches 8 bytes when a PCI Memory
Read command is decoded.
The Memory Read Multiple command results in a prefetch read of a minimum of 32 bytes or the value
programmed into the RD_AMT[2:0] field
—
independent of the MRA bit setting.
The PowerSpan II PCI target read watermarks are defined in
PowerSpan II never prefetches data beyond a 4-Kbyte address boundary regardless of the value
programmed in the RD_AMT field. This boundary corresponds to the processor bus memory
management page size.
When the Target Image Control register is programmed for 4 byte read transactions,
requesting 8 byte reads causes undefined results in the system.
Table 6: PowerSpan II PCI Target Read Watermarks
PCI Command
Prefetch Amount
Memory Read
8 bytes (default) or 1,2,3, or 4 bytes
Depending in the setting in the MEM_IO bit in
the
“PCI-1 Target Image x Control Register” on
Memory Read Line
Minimum of CLINE in the
Miscellaneous 0 Register” on page 255
register
Memory Read Multiple
Minimum of 32 bytes or RD_AMT.