2. PCI Interface
39
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
BAR_EN
R/W
Enables the PCI Base Address register. When this
bit is set, the Px_BSTx Register is R/W and visible
to Processor Bus access and PCI memory cycles.
When this bit is cleared, the Px_BSTx register
returns only zeros on a read. Writes will have no
effect on Px_BSTx when this bit is cleared.
Enabled or configurable
through EEPROM
BS[3:0]
R/W
Sets the block size of the PCI target image. The
size of the image is 64Kbyte * 2
BS
.
Default value is 0, can be
programmed through any
port after reset or loaded
through EEPROM.
MODE
R/W
Maps the incoming PCI transaction to either
memory or I/O space on the alternate PCI bus.
Default value is 0 (Memory
command generation)
DEST
R/W
Directs the incoming PCI transaction to either the
processor bus or the alternate PCI interface.
Defaults to processor bus
MEM_IO
R/W
Commands to the corresponding image generates
Memory Read commands on the destination PCI
bus (Py) with the same byte enables latched from
the source bus transaction PowerSpan II is
capable of performing 1,2,3, or 4 byte memory
transfers on the PCI bus(es).
Default value is 0 (Regular
I/O mode)
RTT[4:0]
R/W
A 5-bit value, defined in the processor bus
protocol, is generated on the PB_TT lines during a
read on the processor bus.
Defaults to Read
GBL
R/W
Controls the assertion of the PB_GBL_ cache
control signal.
Asserts PB_GBL_
CI_
R/W
Controls the assertion of the PB_CI_ cache
control signal.
Asserts PB_CI_
WTT[4:0]
R/W
A 5-bit value, defined in the processor bus
protocol, is generated on the PB_TT lines during a
write on the processor bus.
Defaults to Write with Flush
PRKEEP
R/W
Enables PowerSpan II to keep prefetch read data
over subsequent transactions (see
Disabled
END[1:0]
R/W
Sets endian mapping to little-endian, PowerPC
little-endian, or big-endian (see
Big-endian is the default
mode.
Table 5: Programming Model for PCI Target Image Control Register
Bits
Type
Description
Default Setting