PCI Interface Functional Overview
Delayed Read
Copyright © 2002 Marvell
CONFIDENTIAL
Doc. No. MV-S300165-00, Rev. A
May 21, 2002, Preliminary
Document Classification: Proprietary Information
Page 49
Since the internal PCI arbiter is disabled by default (the MPP pins function as general-purpose inputs), changing
the configuration can only be done by the CPU or through serial ROM initialization. The CPU or serial initialization
must configure the MPP interface to their appropriate functionality through the MPP Control registers, at offsets
0xf000, 0xf004, 0xf008, and 0xf00c, and then enable in the Arbiter Control register’s
EN
bit [31], at offsets 0x1d00
and 0x1d80.
When the internal PCI arbiter is enabled, the REQ* and GNT* pins to the GT-64260A PCI master unit are inter-
nally connected. Pull down the GNT* pin and leave the REQ* pin unconnected in the GT-64260A PCI interfaces
(PCI0 and PCI1).
For more information on the internal PCI arbiter, see the GT-64260A datasheet’s "Internal PCI Arbiter" section.
Notes
•
Since the MPP default configuration is general-purpose input, pull ups must be set on all the GNT* and
REQ* pins on the MPP interface.
•
If more than one master is requesting the bus and the PCI Arbiter Control register’s
BDEn
bit [1] and
BV
bits [6:3] are set to ’1’, at offsets 0x1d00 and 0x1d80, a lock situation may occur. A broken value
implies that if a frame was not asserted one cycle after GNT* was asserted the arbiter can grant the
bus to another master. In the configuration cycle, the GT-64260A uses address stepping (drives the
address and command for one cycle before asserting frame). This means that the configuration cycle
might never go to the bus.
5.3
Delayed Read
The GT-64260A uses delay reads for all read transactions. The only way to avoid delayed read is in the following
settings:
•
For memory read: Read line and read multiple transactions configure the corresponding PCI region to all
aggressive prefetch bits disabled, delayed read disabled, and prefetch enabled. The PCI Access Control
Base (Low) register, at offsets 0x1e00 and 0x1e80:
–
RdMulPrefetch
and
RdLinePrefetch
bits [18:17] set to '00'.
–
DReadEn
and
PrefetchEn
bits [13:12] set to '00'.
•
For configuration read: Disable the slave sync barrier in the PCI Command register’s
SBDis
bit [13], at offsets
0x1c00 and 0x1c80.
•
All IO reads are treated as delayed read.
5.4
32-bit PCI System
The GT-64260A can be configured to work in a 32-bit PCI bus mode. Each PCI interface (PCI0 and PCI1) can be
individually configured to 32- or 64-bit modes.
REQ5*
MPP11
MPP27
GNT5*
MPP10
MPP26
Table 12:
Internal PCI Arbiter in Multiplexing (Continued)
PCI Pins
Optional Multiplexing on MPP Pins