Revision 1.02 – June 27, 2006
S5935 – PCI Product
Data Book
Pass-Thru Operation
FIFO PCI Bus Mastering Operation
Pass-Thru operation executes PCI bus cycles in real
time with the Add-On bus. This allows the PCI bus to
directly read or write to Add-On resources. The S5935
allows the designer to declare up to four individual
Pass-Thru Regions. Each region may be defined as 8,
16-, or 32-bits wide, mapped into host memory or I/O
space and may be up to 512MB bytes in size. Figure 4
right shows a block diagram of the S5935 Pass-Thru
architecture.
FIFO PCI Bus Master data transfers are processed by
one of two 8-DWORD FIFOs. The FIFO block diagram
is shown in Figure 5. The particular FIFO selected for
a data transfer is dependent only on the direction of
data flow and is completely transparent to the user.
Internal S5935 decode logic selects the FIFO that is
dedicated to transferring data to the other bus.
The way data is transferred by a FIFO, is determined
by Operation and Configuration Registers contained
within the S5935. A FIFO may be configured for either
PCI or Add-On initiated Bus Mastering with program-
mable byte advance conditions, read vs. write
priorities and Add-On bus widths. Advance conditions
allow the FIFO to implement 8-, 16- or 32-bit bus
widths. Configuring the S5935 for Bus Master opera-
tion enables separate address and data count
registers, which are loaded with the PCI memory
address location and number of bytes to be read or
written. This is accomplished by either the Host CPU
or Add-On logic. Data can be transferred between the
two buses transparent to the PCI Host processor, how-
ever, the Add-On logic is required to service the S5935
Add-On Local bus. An indication of transfer completion
can be seen by polling a status register done bit or
S5935 signal pin or enabling a ‘transfer count = 0’
interrupt to either bus.
Pass-Thru operations are performed in PCI target only
mode, making this data channel useful for converting
existing ISA or EISA designs over to the fast PCI
architecture. The Pass-Thru data channel utilizes sep-
arate Add-On bus signal pins to reflect a PCI bus read
or write request. Add-On logic decodes these signals
to determine if it must read or write data to the S5935
to satisfy the request. Information decoded includes
PCI request occurring, the byte lanes involved, the
specific Pass-Thru region accessed and if the request
is a burst or single-cycle access. All requested Pass-
Thru address and data information is passed via Add-
On Operation Registers.
Pass-Thru operation supports single PCI data cycles
and PCI data bursts. During PCI burst operations, the
S5935 is capable of transferring data at the full PCI
bandwidth. Should slower Add-On logic be imple-
mented, the S5935 automatically issues PCI bus waits
or a Host retry indication until the requested transfer is
satisfied.
Further FIFO configuration bits select 16, 32, or 64 bit
Endian conversion options for incoming and outgoing
data. Endian conversion allows an Add-On processor
and the host to transfer data in their native Endian for-
mat. Other configuration bits determine if the Add-On
Local bus width is 8, 16 or 32 bits. 16-bit bus configu-
rations internally steer FIFO data from the upper 16
bits of the DWORD and then to the lower 16-bits on
alternate accesses. FIFO pointers are then updated
when appropriate bytes are accessed. Other methods
are available for 8-bit or 16-bit Add-Ons.
Figure 4.
S5935
Add-On Pass-
Address Latch
Thru Address
Register
Add-On Pass-Thru Write Data
Add-On Pass-Thru Read Data
Efficient FIFO management configuration schemes
unique to the AMCC S5935 specify how full or empty a
FIFO must be before it requests the PCI Local bus.
These criteria include bus requests when any of the 8
DWORDs are empty, or when four or more DWORDs
are empty. This allows the designer to control how
often the S5935 requests the bus. The S5935 always
attempts to perform burst operations to empty or fill the
FIFOs. Further FIFO capabilities over the standard
register access methods allow for direct hardware
FIFO access. This is provided through separate
access pins on the S5935. Other status output pins
allow for easily cascading external FIFOs to the Add-
On design.
AMCC Confidential and Proprietary
DS1527
19
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
