The Realization of PCI Communications Based on the FPGA and

IJCSNS International Journal of Computer Science and Network Security, VOL.6 No.2B, February 2006
The Realization of PCI Communications
Based on the FPGA and PCI9656
LIU Weichen, JI Zhenzhou and TANG Shuofei,
Dept. of Computer Science and Engineering, Harbin Institute of Technology, Harbin, China
The paper introduced the design of the data channel between the
hardware firewall and the host computer based on the advanced
Virtex-II-series FPGA from Xilinx, Inc. and the bridge chipPCI9656 from PLX Technology. The design of FIFO with
double channels, double ports and double clocks, three control
logics and the queue descriptors makes it a high work frequency
and transfer speed, then a good performance in capability and
Key words:
FPGA, PCI9656, FIFO, Descriptor
The design of the PCI interface is under the demand of the
“Gigabit Hardware Firewall”. The function of the interface
is to construct a communication channel between the host
computer and the firewall. Accordingly, the host can
receive messages from the firewall, send control messages
the firewall, expand the functions of the firewall, and
improve the flexibility of the firewall. As we know, PCI
bus is the most widely used high speed synchronous bus.
At present, PCI bus with bus width of 32 bits, clock
frequency of 33 MHz and highest transfer speed of 132
Mbps is used in most PCI applications, and it can not
satisfy the demand of the progressive data processing [1].
Especially, the demand is more rigorous to transfer data at
a high speed between the host and the hardware firewall
used in the core of the network. Thereby, it is a good
resolvent to develop the new applications based on the
PCI bus criterion with bus width of 64 bits, clock
frequency of 66 MHz and highest transfer speed of 528
Mbps. PCI9656 is a 64-bit & 66 MHz PCI interface chip
presented by PLX Technology, and it has a good
performance in flexible connection and I/O acceleration
[2]. Using PCI9656 to develop the PCI bus interface can
shorten the developing periods, reduce the developing
difficulty and get good capability. With the cooperation of
the other modules on the firewall, it realizes the whole
functions of the firewall to design the interface logic and
communication module with PCI9656 on the FPGA.
2. Design Principle
In the interest of expanding the functions of the board
adapters, PLX Technology brings out PCI9656 to provide
a high-powered object-mode PCI bus interface. The circuit
can provide 64-bit mini PCI bus object interface for use of
adapters. The target of the paper is to design a channel for
data transfer between PCI9656 and the firewall, and it
meets the request of speed and stability. Then, as shown in
Figure 1, a whole “data channel“ between the host
computer and the firewall is set up when the driver of
PCI9656 is correctly installed at the host, and the
appropriative application software is written based on the
Fig. 1 The Diagram of PCI Data Channel
Based on the advanced Virtex-II series FPGA made by
Xilinx Inc., what is to be designed is realized with Verilog
HDL. Therefore, first of all, we should know some
necessary background information and knowledge of this
FPGA and PCI9656.
2.1 Characteristic of Xilinx Virtex-II FPGA
The products of Virtex-II series are high-powered flatlevel logic parts which are designed with 0.15-micron and
Manuscript received February 25, 2006.
Manuscript revised February 28, 2006.
IJCSNS International Journal of Computer Science and Network Security, VOL.6 No.2B, February 2006
8- layer coherer technics. Its characteristic is listed below
Clock frequency inside attains to 420 MHz, and inout frequency to 840 MHz.
Interior memories are made up by the high-powered
SelectRAM structure, the capacity of every block
RAM is 18Kb, and it supports the operation on both
ports at the same time. It supports the high-powered
exterior memory interface, SDR/DDR
interface included.
There are maximum of 93,184 registers/flip-latches
droved by clock, and maximum of 93,194 LUTs and
shift-registers based on the LUTs. It supports aclinic
cascade connection chain, “multiplication
accumulating” multiplex selector, and the ample and
flexible interior logic resources made up by tristate
bus framework.
There are 12 DCM modules and 16 clock multiplex
buffers at most, and they make up of the abundant
and efficient interior clock resource. Accordingly,
flexible system clock solutions are provided.
Fig. 2 PCI 9656 Block Diagram [5]
The excellent functions and capabilities of the product and
the integrated support software environment provide great
advantage for the development.
2.2 PCI9656
PCI 9656 Block Diagram is shown in Figure 2. It adopts
the PLX Data Pipe Architecture, has DMA engine,
programmable master controller, dependent data transfer
mode and PCI info transfer. It can build a PCI interrupt
INTA by 2 local bus interrupt LINTi and LINTo. Local
clock and PCI clock work asynchronously, and local bus
clock is independent of the PCI clock [3]. All these
characteristics help to make decision of designing the
required module. Choose DMA mode to transfer data,
choose interrupt for communications with the host, and
design asynchronous high speed local part from the PCI
3. Function Design
As shown in Figure 3, the PCI module is made up of 5
parts: PCI controller, receiver queue, receiver controller,
sender queue, sender controller. The two FIFOs save up
the data, the PCI controller communicates with PCI9656
to connect to the host part, and the receiver controller and
the sender controller communicate with the scheduler of
the FPGA to connect to the Local part.
Fig. 3 PCI module frame diagram
Data management
Because the block mode of PCI9656’s DMA is chosen for
data transfer, how to express the length and the available
length of the data package in transfer must be considered.
If only the original data is packed, the length information
can not be acquired. The solution of the paper is to add a
piece of 32-bit head information to the original data
package for the transfer at one time. The head information
can identify the available length of the data package and
the available width of the last data in the package.
FIFO design
In consideration of the request of the system, two FIFO
channels are created to store the up data and the down data
separately for the credible data transfer. Read and write
operations on one FIFO can be done at the same time by
using the RAM with a pair of ports and it definitely
improves the efficiency of the data transfer. For the best
utilization of the FIFO resources, the read and write
operations are controlled under different clocks. At the
IJCSNS International Journal of Computer Science and Network Security, VOL.6 No.2B, February 2006
PCI part, the clock of the PCI bus – 66 MHz is used. At
the Local part, the uniform clock of the board – 125 MHz
is used. Therefore, the data storage has the characteristic
of double channels, double ports and double control
clocks, and the superiorities of parallelism and
asynchronism are utilized here.
The Block SelectRAM Memory RAMB16_S36_S36
which is provided inside the FPGA is adopted as the basis
memory of the two FIFOs. As shown in Figure 4,
RAMB16_S36_S36 is indeed the two-port RAM. It
contained a storage area of 18kb and two unattached
visiting ports A and B. The two ports have independent
functions and symmetrical structure, and the different visit
to the storage can go along at the same time. Data can be
written and read from either port. Every port is
synchronous, and it owns clock of itself. These
characteristics nicely satisfy the above requirement.
32-bit binary. It contains two pieces of information: the
size and the first address of the free space in the queue.
Then, via the total size of the queue, we can know the size,
and then the first address of the data space. Thereby, all
the information of the FIFO is collected.
A descriptor composed of the size and the first address of
the free space of the FIFO is chosen to meet the need of
the specific visit to the FIFO in the design of the firewall.
Other designers can discretionarily choose the
combination of the four states of the FIFO to describe it
for your personal purpose of efficiency and optimization.
The principle of updating the descriptor is to keep the
integrality of the data. The time of updating the descriptor
is immediately after the whole package transfer finished,
and the next transfer must start after the update is over.
During the maintenance of the descriptor, there are some
problems in “read-write” conflict and asynchronism. The
design must follow the principle of keeping the integrality
of the data, the write of the descriptor must execute after
the read of the descriptor finished, and the asynchronous
conflict must be managed with great caution.
The descriptor is a big bright spot of the design. Two
simple 16-bit binaries and two simple shift operations
provide all the needed size and address information for the
read and write of the FIFO. The existence of the
descriptors greatly reduces the complexity of the queue
operations, affords many facilities for the design of the
controllers, and consequently improves the efficiency.
Fig. 4 The Block Diagram of SRAM Frame
Many factors must be considered when choosing the
capacities of the two FIFO, such as the attribute of the data
for transfer, the attribute of the data flux, the gross of the
rams in the FPGA and its allotment. In our case, the length
of the data package is changeless, and the flux of the
package is stable correspondingly, so the access to the
FIFOs is reversely easy to control for the burst condition
is infrequent. Because the word length of the data for
storage is commonly big, the mode of word expanding is
used for the connection of the rams.
The management method of the FIFO data storage is
ordinal cycle, and the general information of the FIFOs is
in the descriptors.
Descriptor design
The descriptor is designed to describe the state of the
FIFO. The two descriptors of the two FIFOs provide the
whole useful information for visiting. The descriptor is a
Receiver/sender controller design
When the receiver/sender controller is in the process of
transfer, the part which sends the sending signal must send
the length of the waiting data package at the same time.
The receiver part judges the time to respond. After the
sender part receives the answer signal, starts the transfer
and finishes it, the receiver/sender controller should
update the descriptor and turn into the state for the next
transfer, besides canceling the transfer control signal to
inform the accomplishment.
PCI controller design
There are two visit modes from PCI9656 to the PCI
controller: visiting the descriptors in the mode of Direct
Slave, and visiting the data areas of the FIFOs in the mode
of DMA. Since PCI9656 is also the sponsor in the DMA
mode, the PCI controller is always working as the
secondary device and the control signals used in the two
modes are absolutely the same.
Because there is only one device on the local bus, all
storages (two FIFOs and descriptors included) can be
IJCSNS International Journal of Computer Science and Network Security, VOL.6 No.2B, February 2006
addressed uniformly. Thereby, the two different kinds of
visit can be differentiated by the address signals, also can
the visit to the different FIFOs. Because PCI9656 visits
the up queue and the descriptors only for read and the
down queue only for write (the descriptors can only be
updated by FIFO controllers), the address method makes
the address signals take powerful information – they can
differentiate between read and write, and they can
differentiate the object for read and write.
Fig. 5 DMA PCI-to-Local Timing Diagram
Fig. 6 DMA Local-to-PCI Timing Diagram
The ready signal is the key factor that ensures the PCI part
to accomplish a correct transfer and keep stable. The speed
of the memory affects the enactment of the ready signal
very much and it differs a lot in actual applications. As
shown in Figure 5, when data is written to the FIFO, the
PCI controller can send the ready signal at once, because
the needed address and data information for write has been
prepared by PCI9656. As shown in Figure 6, when data is
read from the FIFO, the PCI controller should send the
ready signal after one cycle, because moving the data from
FIFO to the bus needs one cycle. When the descriptor is
read, the ready signal can be sent at once too, because the
descriptor data stored in registers can be on the bus
immediately. Anyway during the interface design, the
affirmance of the ready signal is affected by many factors.
Much theoretic analysis and practical consideration must
be synthesized. As a result, it becomes the biggest
difficulty in detail, and must be especially cautious in the
process of design.
4. Performance Analysis
Capability and stabilization are the biggest request to the
design of the data channel with no interest in the data
content. All the designs in the paper are debugged and
tested in the Xilinx integrated develop environment – ISE,
emulated in Modelsim, synthesized in Synplify, and online
debugged in ChipScope. The interface to the OS is the
SDK software PLXMon powered by PLX Technology.
Snifer is used to capture packages in the network for
testing. Particularly, PLXMon can get real-time register
information of PCI9656, as well as the important
parameters for the DMA transfer. It supplies huge
convenience to the “visual” online debug. Being familiar
with PLXMon and making good use of it can greatly
reduce the debug difficulty.
The analysis is processing in two parts: testing the up
queue and the down queue. To test the up queue, data
packages are brought by network device, and then they
pass the firewall and reach the scheduler. The up FIFO
incepts them under the control of the receiver controller,
the PCI controller sends them to PCI9656, PCI9656 sends
the data packages rightly to the memory buffer under the
command of PLXMon, and then the validity of the transfer
can be checked. Whereas, to test the down queue,
PLXMon first sends data packages from the memory
buffer to PCI9656, then they are written into the down
FIFO under the control of the PCI controller, the sender
controller sends them to the scheduler, they pass the
firewall and are captured by Snifer, and the validity is
checked at last.
Stabilization analysis
Because the design serves for the hardware firewall, very
little data transfer with high data density is occurred in
actual applications, and then the stabilization is the most
important capability aim. In our design, the synthesizing
frequency of the local part is high to 154.9 MHz. It
exceeds the actual work clock 125 MHz by a great deal.
Moreover, the synthesizing frequency of the PCI part
exceeds the actual work clock 66 MHz more and is high to
112.1 MHz. As a result, the whole module works fairly
stably. It performs good conditions in the test, too. In the
test to the firewall that lasts for seven continuous days, the
module runs stably and the ratio that the false code
appears when sending and receiving data is zero.
Capability analysis
Under the precondition of the stabilization, the design
gives attention to the improving of the capability. For the
unconventional FIFO design with double channels, double
ports and double clocks and the descriptor system, the
throughput rate of the interface is improved greatly. In the
IJCSNS International Journal of Computer Science and Network Security, VOL.6 No.2B, February 2006
test, the visual speed is high to 287.04 Mbps (restricted by
the experiment and the actual speed terminal maybe
higher), and it attains a high standard of the capability of
the 64-bit, 66 MHz PCI bus.
Other analysis
The condition that the module occupies the percentage of
the FPGA resources is as follows:
Total LUTs:
469 (1%),
Block Rams:
6 of 96 (6%),
Register Bits:
442 (1%).
It is obvious that the design consumes only a few
resources and takes tiny burden to the system. Due to the
apt choice of the number matching of the Block Rams, the
data throughput is abundant to a high standard. The design
accords tightly with the conception of high capability and
low cost.
5. Conclusions
The paper introduces the way of setting up the data
channel between the local and host using PCI9656. It
provides the communication interface to the host computer,
and realizes the basis of the function configuration,
extensibility control and information feedback to the user
for the hardware firewall. It provides the resolvent of high
speed PCI transfer based on PCI9656. Its practical
frequency 154.9MHz can absolutely satisfy the request of
high speed and stabilization. Since the design principle
and realization method of the module, based on the
powerful functions and simple user interface of PCI9656,
fast local bus interface development with low resource
usage and good performance can be widely generalized
into the applications based on the high speed PCI bus.
[1] Hu Heping, Tian Yibo, Design of PCI Interface Based on the
FPGA, Computer Engineering, 2003(8)
[2] Tom Shanley, Don Anderson, PCI System Architecture
Fourth Edition, Publishing House of Electronics Industry, 2000.7
[3] Xu Jian, Dai Zibin, 64-bit PCI bus interface circuit PCI9656
and its application, International electronic elements, 2005(8)
[4] Xilinx, Inc., Virtex-II Platform FPGA User Guide,, 2001.4.2
[5] PLX Technology, Inc., PCI 9656BA Data Book,, 2003.11
LIU Weichen
received the B.S. degree in Computer
Science and Engineering from Harbin Institute of Technology in
2004. Now, he is a graduate student in Computer Science and
Engineering in Harbin Institute of Technology. His major
research interest is computer system architecture. He has
published four papers in the field.
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