12. Register Descriptions
301
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
12.5.30
Processor Bus to PCI-2 Interrupt Acknowledge Cycle Generation Register
This register is used to generate an Interrupt Acknowledge cycle originating on the Processor Bus and
destined for the PCI-2 bus. Reading this register from the Processor Bus causes an IACK cycle to be
generated on the PCI bus. The byte lanes enabled on the PCI bus are determined by PB_SIZ[0:3] and
PB_A[30:31] of the Processor Bus read cycle. The address on the Processor Bus used to access the
PB_P1_IACK register is passed directly over to the PCI bus during the PCI IACK cycle. However this
has no effect because address information is ignored during PCI IACK cycles.
If the Address Retry Enable (ARTRY_EN)) bit is set, in the
“PCI-1 Miscellaneous 1 Register” on
, the Processor Bus Master is retried until the read data is latched from the PCI target. When
the IACK cycle completes on the PCI-2 bus, the IACK_VEC[31:0] field is returned as read data when
the Processor Bus Master returns after the retry.
Writing to this register from the Processor Bus, or either PCI bus, has no effect. Reads from the PCI
bus return all zeros.
The END bit in the
“Processor Bus Register Image Base Address Register” on page 295
selects the
endian conversion scheme used for accesses to PCI through this register. The definition of endian
conversion scheme is for PCI accesses, not register accesses.
This register is not implemented in the Single PCI PowerSpan II and must be treated as reserved.
Register Name: PB_P2_IACK
Register Offset: 0x2A4
PCI
Bits
Function
PB
Bits
31-24
IACK_VEC
0-7
23-16
IACK_VEC
8-15
15-08
IACK_VEC
16-23
07-00
IACK_VEC
24-31
Name
Type
Reset
By
Reset
State
Function
IACK_VEC[31:0]
R
PB_RST
0
PCI IACK Cycle Vector