This paper discusses the design and verification of an IP core bridge for interfacing the AMBA AXI-Lite and APB buses, aimed at enhancing communication between different frequency operating buses in System-on-Chip (SoC) systems. The proposed APB bridge operates at a maximum frequency of 168.464 MHz, converting read and write operations from the AXI bus to the APB bus. The document details the design methodology, features of AMBA 4.0, and includes simulation results confirming the functionality of the bridge module.

1. Short Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
Design and Analysis of Xilinx Verified AMBA Bridge
for SoC Systems
Shaila S Math1, Veerabhadrayya Math2
1
BMS Institute of Technology, Department of Electronics and Communication Engineering, Bangalore, India
Email: shaila.s.math@gmail.com
2
Srinivas School of Engineering, Department of Electronics and Communication Engineering, Mangalore, India
Email: veerabhadrayya.math@ymail.com
Abstract: ARM introduced the Advanced Microcontroller Bus
Architecture (AMBA) 4.0 and its specifications define five
buses/interfaces: Advanced eXtensible Interface Bus (AXI),
Advanced High-performance Bus (AHB), Advanced System Bus
(ASB), Advanced Peripheral Bus (APB) and Advanced Trace
Bus (ATB). That means more and more existing Intellectual
Property (IP) must be able to communicate with AMBA4.0
bus. This paper presents an IP core design of APB Bridge, to
provide interface between AXI-Lite bus and APB bus operating
at different frequencies. The maximum operating frequency
of the module is 168.464MHz. Test cases are run to perform
multiple read and write operations. Synthesis and Simulation
is done using Xilinx ISE and Modelsim.
Index Terms: AMBA, AXI, IP, Xilinx
Figure 1. System On-chip Interconnect showing AMBA/
CoreConnect/ Wishbone Buses
I. INTRODUCTION
The AMBA data bus width can be 32, 64, 128 or 256 byte,
address bus width will be 32bits wide. The AMBA AXI4 [5]
specification to interconnect different modules in a SoC was
released in March 2010. The key features of AMBA4 including its all versions (AXI4 and AXI4-Lite) are discussed in
detail in [5]. Few key features used in designing the modules
are discussed here.
In recent years due to the miniaturization of
semiconductor process technology and computation for
survival in the current market conditions constant
customization is required. The semiconductor process
technology is changing at a faster pace during 1971
semiconductor process technology was 10µm [1], during 2010
the technology is reduced to 32nm and future is promising
for a process technology with 10nm. Intel, Toshiba and
Samsung have reported that the process technology would
be further reduced to 10nm in the future. So with decreasing
process technology and increasing consumer design
constraints System-on-Chip (SoC) has evolved, where all the
functional units of a system are modeled on a single chip.
SoC buses are used to interconnect an Intellectual
Property (IP) core to the surrounding interface. These are
not real buses, but they reside in Field Programmable Gate
Array (FPGA). Each bus/interface have different features,
the designer chooses the bus, best suited for his application.
Some challenges faced in SoC buses are latency, high
bandwidth, arbitration schemes, number of masters and slaves
connected on bus and performance of bus according to
different application. Fig. 1 shows the exact picture where
the SoC buses reside in a chip. Masters can be Central
Processing Unit (CPU), Moving Picture Expert Group (MPEG),
where as slaves can be memory, Arithmetic and Logical Unit
(ALU) etc. Currently there are a few publicly available systemon-chip buses such as AMBA from ARM [2], Core Connect
from IBM [3], Wishbone from Silicore [4] and others. The
number of masters and slaves depends on application.
© 2013 ACEEE
DOI: 03.LSCS.2013.2.535
A. AMBA AXI4
Features of AXI4 includes the following:
• Burst lengths up to 256 beats is supported
• Quality of Service (QoS) signaling
• Multiple region interface is supported
• Write response requirements are updated
• Update of AWCACHE and ARCACHE signaling details
• For ordering requirements additional information is provided
• Optional User signaling details
• Locked transactions and write interleaving are removed
B. AMBA AXI4-Lite
Features of AXI4-Lite interface are:
• All transactions burst length is 1
• All data access size is same as width of data bus
• Supports 32-bit or 64-bit data bus width
• All accesses are equivalent to AWCACHE or ARCACHE
equal to b0000
• For exclusive accesses support is not provided.
C. AMBA APB
The APB bus is optimized for minimal power consumption
and reduced interface complexity. The APB peripherals can
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2. Short Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
TABLE 1: SIGNAL D ESCRIPTIONS
be integrated easily to any design flow, with the following
advantages:
• High-frequency operation can be easily achieved
• Use of a single clock edge to simplify the static timing
analysis
• No special considerations are required for automatic test
insertion
• Many Application Specific Integrated Circuit (ASIC) libraries
have a better selection of rising edge registers
• Easy integration with cycle-based simulators.
AMBA B RIDGE
Signal
Input/
Output
Global
Input
AResetn
AWADDR
WSTRB
Global
Master
Master
Input
Input
Input
AWPROT
Master
Input
WDATA
ARADDR
Master
Master
Input
Input
ARPROT
Master
Input
RDATA
Master
Input
AWVALID
Master
Output
AWREADY
Slave
Output
WVALID
ARVALID
RVALID
WREADY
BRESP
RRESP
Master
Slave
Slave
Slave
Slave
Slave
Output
Output
Output
Output
Output
Output
BVALID
Slave
Output
BREADY
RREADY
Master
Master
Output
Output
ARREADY
Slave
Output
PCLK
Global
Input
PRESETn
All five channels of AMBA use the same VALID/READY
handshake to transfer data and control information. Both
master and slave are controlled by this two way mechanism.
When the data or control information is available on the
source it generates VALID signal. The destination generates
the READY signal to indicate that it accepts the data or
control information. When both the VALID and READY
signals are HIGH transfers will occur. On both master and
slave interfaces there must be no combinatorial paths between
input and output signals. Table 1 gives the information of
signals used in the complete design of the module.
Fig. 2 to Fig. 4 show examples of the handshake sequence.
In Fig. 2, the source drives the VALID signal HIGH when it
gets data or control information. The destination drives
READY signal HIGH if it is ready to accept the data or
information sent by the source. The arrow shows when the
transfer occurs. It is not permitted to wait until READY is
asserted before asserting VALID. Once VALID is asserted it
must remain asserted until the handshake occurs.
Source:
master/
slave/APB
Bridge
Aclk
D. Handshake Mechanisms of AXI-Lite and APB
Global
APB
bridge
APB
bridge
APB
bridge
APB
bridge
Input
Global clock
signal.
Global reset signal
Write address
Write burst type
Write protection
type
Write data
Read address
Read Protection
type
Read data
Write address
valid
Write address
ready
Write valid
Read address valid
Read valid
Write ready
Write response.
Read response.
Write response
valid.
Response ready.
Master ready.
Read address
ready.
Global clock
signal
Global reset signal
Input
APB address bus
Input
Protection type
PADDR
PPROT
PSELx
PENABLE
PWRITE
Figure 2. VALID before READY handshake
PWDATA
In Fig. 3, before the data or control information is valid,
destination drives READY HIGH. The data or control
information is accepted in a single cycle, as soon as it becomes
valid. The arrow shows when the transfer occurs. It is
permitted to wait for VALID to be asserted before the
corresponding READY is asserted. If READY is asserted, it
is permitted to de assert READY before VALID is asserted.
In Fig. 4, both the source and destination drives READY
and VALID signal at the same cycle. Here the transfer can be
data or control information. In this case the transfer occurs
immediately. The arrow shows when the transfer occurs.
In this paper interfacing bridge of AXI4-Lite and APB [6]
is designed and verified. Here we used Verilog HDL [7] (Hardware Description Language) for designing the RTL (Register
Transfer Level) code. Synthesis and Simulation is done using Xilinx ISE and Modelsim [8]. The rest of the paper is
organized as follows: Section 2 discusses related work. Sec
© 2013 ACEEE
DOI: 03.LSCS.2013.2.535
OF
PSTRB
PREADY
PRDATA
PSLVERR
Input
Input
APB
bridge
APB
bridge
APB
bridge
Slave
interface
Slave
interface
Slave
interface
Description
Select line for
Slave
Enable signal
indicates the
second and
subsequent cycles
of an APB transfer
Input
Direction
Input
Write data
Input
Write strobes size
Output
Response ready
Input
Read data
Output
Transfer failure
Figure 3. READY before VALID handshake
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3. Short Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
Lite of the AMBA on the simulator Riviera was discussed in
[24]. IP solutions for AMBA interconnect was discussed in
[25].
III. PROPOSED WORK
In this work an IP core of APB bridge is designed to provide interface between AXI-Lite bus and APB bus operating
at different frequencies. The maximum operating frequency
of the module is 168.464MHz. The APB bridge provides an
interface between the high-performance AXI domain and the
low-power APB domain. It appears as a slave on AXI bus but
as a master on APB that can access up to sixteen slave peripherals. Read and write transfers on the AXI bus are converted into corresponding transfers on the APB. The AXI4Lite to APB Interfacing module block diagram is shown in
Fig. 5. The test layer shown in the Fig. 5 tests the module for
multiple read and write operations.
Figure 4. VALID with READY handshake
tion 3 of this paper, discusses proposed work. In Section 4,
simulation parameters and results are discussed. Future scope
and concluding remarks are given in Section 5.
II. RELATED WORK
Milica Miti and et al gives the survey of various buses
On-Chip Buses [9]. Computer architecture [10] defines the
physical structure of the CA. Types of computer architecture
are single shared bus, hierarchical bus, token ring bus,
crossbar bus or custom networks. Protocols are defined for
communication channels/buses. Each bus/interface have
different features, the designer chooses the bus, best suited
for his application. Various on-chip bridging techniques in
short are discussed in this section.
AMBA’s design methodology and set of specifications
that will aid designers in making detailed comparisons with
other buses was discussed in detail in [11].
Designing AHB/PCI bridge was discussed in [12]. Here
function of AHB/PCI bridges to map various control signals
and address spaces from one bus into those of another was
explained in detail.
On-chip communication architectures for reconfigurable
System-on-Chip [13] surveys existing solutions for SoC and
analyses the suitability for SoC application. In [14] multichannel on-chip-bus architectures for system-on-chips were
discussed. An on-chip bus bridge between heterogeneous
buses with different clock frequencies was discussed in [15].
Design and implementation of AXI bus protocol-based on
MPSoC architecture was discussed in [16] which uses Altera
Stratix II EP2S180 Field Programmable Gate Array (FPGA).
An IP core of APB bridge, which translates the AXI4.0-lite
transactions into APB 4.0 transactions was discussed in detail
in [17] and [18].
In [19] the analysis was carried out by simulating a multicore platform with a shared-link AXI backbone running a
video phone application. The performance was evaluated in
terms of bandwidth utilization, average transaction latency
and system task completion time. Design of AHB2APB bridge
simulated using Xilinx and Modelsim was discussed in [20].
AMBA to SoCWire network-on-chip bridge [21] presents an
efficient connection between a SoCWire network and a LEON
processor bus systems. Direct memory access enables the
AHB2SOCW bridge to operate efficiently. Design and
analysis of AMBA AXI4 system for various read and write
operations using VCS tool [22] by Synopsis was discussed
in [23]. The system level modelling of the Advanced AHB© 2013 ACEEE
DOI: 03.LSCS.2013.2.535
Figure 5. Block diagram of AXI4-LITE and APB interface
A. Signal Description
Fig. 6 shows the master and slave component signal
connections. The Interfacing module uses AMBA AXI-Lite
signals and APB signals as described in the AMBA protocol
specification. The read and write operation signals
B. Finite State Machines (FSM)
Fig. 7 shows FSM [26] for operational activities of the
module for read and write operation. When reset signal goes
high the module gets address and data information from test
layer. Either it is read or write operation, the module will wait
for VALID signal.
For read operation the data is read and on reading the last
byte RLAST signal is raised. Acknowledgement signal is
received on end of the operation to master module. If it is a
multiple read operation, than the process is continued or else
new address and data information is received from the test
layer. For write operation the data is written to the destination
location and on writing the last byte WLAST signal is raised.
Acknowledgement signal is received on end of the operation
to master module. If it is a multiple write operation, than the
process is continued or else new address and data information
is received from the test layer.
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4. Short Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
Figure 7. Operational activity of the module
Figure 6. Signals used to design interface between AMBA AXI4 and
APB module
1) Write address operation
Fig.8 shows the FSM for write address operation. In state1
AWVALID is set to zero. When Pending_tran_write_addr_reg
==1 then it transits to state S2. In state2 AWVALID is set to
one. When pending_trans_write_addr_reg =1(more
addresses) it will remain in the same state if there are more
addresses to be transmitted or if AWREADY ==0.
Figure 8. FSM for write address operation
RVALID==1 and RLAST==0 then it will go to state S2. If
RVALID==0 then it will remain in the same state S1. Further
state transitions will be done according to the state diagram
(Fig. 11).
2) Write data operation
Fig.9 shows the FSM for write data operation. In state1 if
WVALID==1 and WLAST==0 then it will go to state S2. If
WVALID==0 then it will remain in the same state S1.
WREADY=0 in state S1. Further state transitions will be done
according to the state diagram (Fig. 9).
3) Read address operation
Fig.10 shows the FSM for read address operation. In state1
ARVALID is set to zero. When Pending_tran_read_addr_reg
==1 then it transits to state S2. In state2 ARVALID is set to
one. When Pending_tran_write_addr_reg==1 then it will
come to this state and remains in the same state until
AWREADY is high && Pending_tran_write_addr_reg==1.
1) Read data operation
Fig.11 shows the FSM for read data operation. In state1 if
© 2013 ACEEE
DOI: 03.LSCS.2013.2.535
IV. RESULT
The timing diagram shown in Fig. 12 illustrates the AXI4Lite to APB Interfacing module operation for various read
and write transfers. Synthesis and Simulation is done using
Xilinx and Modelsim. It shows that when both read and write
requests are active, read is given more priority. For write operation address locations passed to module are 31, 33 and 35;
for read operations 32, 34 and 36.
After synthesis summary reports generated by the tool is
shown in Fig. 13.
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5. Short Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
Figure 9. FSM for write data operation
Figure 12. Simulation results of multiple read and write data
opera tion
Figure 10. FSM for read address operation
Figure 13. Area report of simulation
CONCLUSIONS
AND FUTURE SCOPE
A. Future Scope
The AMBA AXI4 has limitations with respect to the burst
data and beats of information to be transferred. The burst
must not cross the 4k boundary. Bursts longer than 16 beats
are only supported for the INCR burst type. Both WRAP and
FIXED burst types remain constrained to a maximum burst
Figure 11. FSM for read data operation
© 2013 ACEEE
DOI: 03.LSCS.2013.2.535
36

6. Short Paper
Proc. of Int. Conf. on Control, Communication and Power Engineering 2013
length of 16 beats. These are the drawbacks of AMBA AXI4
system which need to be overcome.
[14] Sanghun Lee, Chanho Lee, Hyuk-Jae Lee, “A new multi-channel
on-chip-bus architecture for system-on-chips,” in Proceedings
of the IEEE International SOC Conference, pp.20-27,
September 2004.
[15] Sangik Choi and Shinwook Kang, Mobile SamsungElectronics
Co.,Ltd, “Implementation of an On-Chip Bus Bridge between
Heterogeneous Buses with Different Clock Frequencies”. IEEE,
IDEAS’05, pp. 530-534, July 2005
[16] Fu-ming Xiao, Dong-sheng Li ; Gao-ming Du ; Yu-kun Song
; Duo-li Zhang ; Ming-lun Gao “Design of AXI bus based
MPSoC on FPGA”3rd IEEE international conference on Anticounterfeiting, Security, and Identification in Communication,
ASID 2009, pp. 560-564, August 2009
[17] Jaehoon Song, Juhee Han ; Dooyoung Kim ; Hyunbean Yi ;
Sungju Park “Design Reuse of on/off-Chip Bus Bridge for
Efficient Test Access to AMBA-based SoC”, 16th Asian Test
Symposium, pp. 193 – 198, October 2007.
[18] Chenghai Ma, Zhijun Liu ; Xiaoyue Ma “Design and
implementation of APB bridge based on AMBA 4.0”,
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Communications and Networks (CECNet), pp.193 – 196, April
2011
[19] N.Y.C. Chang, Y.Z. Liao, T.S. Chang, “Analysis of shared-link
AXI” IET Computer Digit. Tech., vol. 3, no. 4, pp. 373–383,
July 2009
[20] Vani.R.M and M.Roopa “Design of AMBA Based AHB2APB
Bridge” IJCSNS International Journal of Computer Science
and Network Security, vol.10 no.11, pp. 14-18, November
2010
[21] H. Michel, F. Bubenhagen, B.Fiethe, H.Michalik,B.Osterloh,
W.Sullivan, A.Wishart, J.Ilstad, S.A.Habinc, “AMBA to
SoCWire network on Chip bridge as a backbone for a Dynamic
Reconfigurable Processing unit” NASA/ESA Conference on
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[22] Synopsys, VCS / VCSi User Guide Version 10.3, , Available
at, www.synopsys.com, March 2008
[23] Shaila S Math, Manjula R.B,S S Manvi, P. Kaunds, “Data
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Engineering (ICONRAEeCE), pp. 423 – 427, Dec 2011
[24] Richa Sinha, Akhilesh Kumar and Archana Kumari Sinha
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Proceedings, September 2000.
B. Conclusion
The APB bridge using Verilog HDL to provide interface
between AXI-Lite bus and APB bus operating at different
frequencies has been designed. APB bridge designed has
got following features: APB master interface and 32-bit slave
interfaces are provided; Clock domains PCLK and ACLK are
completely independent; The designed module supports 16
APB peripherals; READY signal of APB is translated to wait
states on AXI; and AXI gives SLVERR signal if error occurs
on read/write response.
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© 2013 ACEEE
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