Revision 5.01 – November 30, 2005
S5335 – PCI Bus Controller, 3.3V
PASS-THRU OVERVIEW
Data Sheet
Pass-Thru Transfers
Data transfers between the PCI bus and the Add-On
using the Pass-Thru interface are implemented with a
handshaking scheme. If the PCI bus writes to an
S5335 Pass-Thru region, Add-On logic must read the
data from the S5335 and store it on the Add-On. If the
PCI bus reads from a Pass-Thru region, Add-On logic
must write data to the S5335.
The S5335 provides a simple registered access port to
the PCI bus. Using a handshaking protocol with Add-
On card logic, the PCI bus directly accesses resources
on the Add-On. The Pass-Thru data transfer method is
very useful for direct Add-On memory access, or
accessing registers within peripherals on an Add-On
board. Pass-Thru operation requires an external nv
memory boot device to define and configure the
S5335 Pass-Thru regions.
Some applications may require that an address be
passed to the Add-On for Pass-Thru accesses. For
example, a 4 Kbyte Pass-Thru region on the PCI bus
may correspond to a 4 Kbyte block of SRAM on the
Add-On card. If a PCI initiator accessed this region,
the Add-On would need to know the offset within the
memory device to access. The Pass-Thru Address
Register (APTA) allows the Add-On to access address
information for the current PCI cycle. When the PCI
bus performs burst accesses, the APTA register is
updated by the S5335 to reflect the address of the cur-
rent data phase.
The S5335 provides four user-configurable Pass-Thru
regions. Each region corresponds to a PCI Configura-
tion Base Address Register (BADR1-4). A region
represents a block of address space (the block size is
user-defined). Each block can be mapped into mem-
ory or I/O space. Memory mapped regions can request
to be located below 1 MByte (Real Mode address
space for a PC). Each region also has a configurable
bus width for the Add-On bus interface. An 8-, 16-, or
32-bit Add-On interface may be selected, for use with
a variety of Add-On memory or peripheral devices.
For PCI writes to the Add-On, the S5335 transfers the
data from the PCI bus into the Pass-Thru Data Regis-
ter (APTD). The S5335 captures the data from the PCI
bus when TRDY# is asserted. The PCI bus then
becomes available for other transfers. When the Pass-
Thru data register becomes full, the S5335 asserts the
Pass-Thru status signals to indicate to the Add-On that
data is present. The Add-On logic may read the data
register and assert PTRDY# to indicate the current
access is complete. Until the current access com-
pletes, the S5335 responds to further Pass-Thru
accesses with retries.
Pass-Thru features can be used only when the S5335
is a PCI target. As a target, the S5335 Pass-Thru
mode supports single data transfers as well as burst
transfers. When accessed with burst transfers, the
S5335 supports data transfers at the full PCI band-
width. The data transfer rate is only limited by the PCI
initiator performing the access and the speed of the
Add-On logic.
FUNCTIONAL DESCRIPTION
To provide the PCI bus Add-On with direct access to
Add-On resources, the S5335 has an internal Pass-
Thru Address Register (APTA), and a Pass-Thru Data
Register (APTD). These registers are connected to
both the PCI bus interface and the Add-On bus inter-
face. This allows a PCI initiator to perform Pass-Thru
writes (data transferred from the PCI bus to the Add-
On bus) or Pass-Thru reads (PCI bus requests data
from the Add-On bus). The S5335 Pass-Thru interface
supports both single cycle (one data phase) and burst
accesses (multiple data phases).
For PCI reads from the Add-On, the S5335 asserts the
Pass-Thru status signals to indicate to the Add-On that
data is required. The Add-On logic should write to the
Pass-Thru Data Register and assert PTRDY# to com-
plete the access. The S5335 does not assert TRDY#
to the PCI bus until PTRDY# is asserted by Add-On
logic. If the Add-On cannot provide data quickly
enough, the S5335 signals a retry to the PCI bus. This
allows the PCI bus to perform other tasks, rather than
waiting for a slow target.
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