A Review On AMBA AHB Lite Protocol And Verification Using UVM Methodology

9 II February 2021
https://doi.org/10.22214/ijraset.2021.33120

International Journal for Research in Applied Science & Engineering Technology (IJRASET)
ISSN: 2321-9653; IC Value: 45.98; SJ Impact Factor: 7.429
Volume 9 Issue II Feb 2021- Available at www.ijraset.com
© IJRASET: All Rights are Reserved 473
A Review on AMBA AHB Lite Protocol and
Verification using UVM Methodology
Someshvar S1
, Ohileshwari MS2
1
Electronics and communication, RNSIT, India
2
Electronics and communication, RNSIT, India
Abstract: AMBA are the most widely used protocols in soc designs and microcontrollers, they support the interface of modules
on a microcontroller for intercommunication, different types of systems based on their performance are supported by AMBA
protocols and there are various types of AMBA protocol based on their features and advancements. and verification is a
important aspect in the VLSI domain to verify whether the designed circuit works according to the specification and requirement
it plays a major role in the productivity of a semiconductor industry, so in this paper we have reviewed various AMBA protocols
its features, specifications to have a idea of their usage in microcontrollers and the design of AMBA AHB-lite protocol which
describes its operation and features. We have also described about the need of Verification its evolution and the Universal
verification methodology (UVM) it’s features and advantages over conventional verification methods.
Keywords: AMBA, AHB-lite, UVM, Functional Verification
I. INTRODUCTION
Communication protocols in microcontrollers have evolved a long way, right from UART to AMBA protocols, Communication
protocols are a medium for communication for the systems present in a microcontroller with some set of assigned rules. Advanced
microcontroller bus architecture AMBA is a chip interconnect which connects and manages systems or functional blocks in a
microcontroller [1].
AMBA protocols are the most widely used protocols in the microcontrollers nowadays, as they have many features and different
versions based on their specifications.
They are even used in nowadays smartphones, gadgets and a wide range of system on chips. AMBA family consists of many
versions of AMBA protocol they will be classified in this paper further. AMBA AHB- lite is one of them which is a high
performance bus in the AMBA family hence the name Advanced high performance bus, here lite is one of the version of AHB
which has only one master and multiple slaves.
AMBA is widely adopted by many of the industries because of its variety and different versions which can be used across various
microcontrollers [2], AMBA is more compact and flexible then compared to other protocols hence it is more widely used.
Verification is the most important aspect in the VLSI domain [8], all the soc designs which have been designed has to be verified in
order to check its functionality, weather it performs according to the given specifications or not.
Verification increases the productivity of a semiconductor industry but the verification process should be fast and efficient, therefore
to obtain efficient verification we use UVM (universal verification methodology) UVM is a standard methodology which has to be
followed in the verification process it is fast, reusable, efficient and also portable compared to other verification process. In this
paper we give a overview on the types of AMBA protocols and discuss AHB-lite in detail. And discuss about verification of
designs, evolution of verification and importance of UVM in industries.
II. BACKGROUND
A. AMBA Classification
AMBA protocols are classified into various types based on their specifications, By these number of classifications AMBA protocols
are used across various microcontrollers and SOC’s making them platform independent and to be used with any processor
architecture [9].

Figure 1: AMBA classification
Figure 1 shows the different types of AMBA protocols, ARM introduced AMBA and is a trade mark of ARM ltd. [9] it was
introduced in 1996 the first one to roll out of AMBA family was the ASB (Advanced system bus) and the APB (Advanced
peripheral bus) in its AMBA 2 in 1999 later ARM introduced AHB(Advanced high performance bus), Then in 2003 third generation
AMBA ie: AMBA 3 was introduced including AXI (Advanced extensible interface) and the ATB which is the (Advanced trace bus)
, then AMBA 4 was introduced in 2010 which included AXI4, then in 2011 ACE(Advanced coherency extensions) was introduced
,later in 2015 AMBA 5 was introduced which included CHI(coherent hub interface) [9].
B. Details of AMBA Version
1) AMBA: The ASB and APB are the first bus of the amba family ASB (advanced system bus) is an high performing bus for 16
and 32 bit systems. Many same signals on an AHB are used for the ASB also. APB (advanced peripheral bus) is a bus used for
low performing systems on a microcontroller, the low performing bus are the peripheral devices in a microcontroller
2) AMBA 2: Amba 2 was introduced in earlier days it is quite older generation of the chip interconnect which included AMBA
AHB which is most commonly used across Arm7, Arm9 and Arm Cortex-M designs [3], it also includes ASB which is a
high performance bus used for 16 and 32 bit systems, it also incudes APB2 a low performance bus used for
peripherals
3) AMBA 3: AMBA 3 is also a older generation system on chip interconnect which included the AMBA AXI (Advanced
extensible Interface) protocol and also introduced ATB (Advanced trace bus) and gave extended improvements on APB and
AHB protocols [9]. AXI provides high-performance high frequency designs, AXI suits for high-bandwidth, low-latency system
designs it enables high-frequency operation without using any of the complex bridges, it also interfaces the requirements of
various range of interconnects and system [4]. It supports five unidirectional channels and enables simultaneous read and write
transactions.[9], ATB transfers the trace information between components of a trace system they are in parallel with the
peripherals which provides visibility for debug purposes. AMBA has advanced the AHB and APB in in AMBA 3 which
introduced the lite version of the AMBA AHB ie: AHB-lite which operates only one master and multiple slaves, and the APB
which includes wait and error report and supports low bandwidth transactions for low performing systems or peripherals in a
microcontroller interconnect.
4) AMBA 4: AMBA 4 gives more advancements to AMBA 3 these include ACE (Advanced coherency extensions), which is the
AXI with additional signalling which is system wide coherency. And some other protocols with is intended to fulfil the
requirements of high bandwidth, high clock frequency components, which makes them a high speed interconnect. [9]. All these
features makes them. Suitable for mobile and consumer electronics. ACE and ACE-lite comes under AMBA 4 ACE is a
protocol which has three additional channels for sharing the data between ACE master cache and cache maintenance control of
hardware [4]. ACE-lite is the lite version of the ACE in which small set of signals that offer input and output. Or in one way
coherency in which ACE masters the cache coherency of ACE-lite masters. They can still snoop ACE master caches but other
masters cannot snoop [9]. AMBA 4 also includes AXI 4 and AXI 4-lite AXI 4 is the advancement to AXI 3 which supports 256
burst lengths and supports multiple region interfaces. AXI 4-lite is the smaller version of AXI4 which is smaller and lite with
burst length of one and some exclusive access are not supported. AMBA AXI stream is also a part of AMBA 4 interconnects

which transfers data unidirectionally from master to slave and it also supports single and multiple data streams in the same
shared wires AMBA AXI stream is ideal for implementation in FPGA. And there are some versions of AMBA ATB which
introduces trace synchronization signalling and synchronization request signalling, AMBA 4 APB version which
includes transaction protection and sparse data transfer to the interface and the AMBA LPI this is a protocol of Q-
channel and P-channel which manages clock and power of SOC components.
5) AMBA 5: AMBA 5 is the latest version of AMBA protocol which includes the CHI (coherent hub interface) , AXI5, ACE5 and
AHB5 which extends its features and offers more performance to align and interface CHI [9], AMBA CHI interfaces the
coherent processors like the cortex A-65, cortex A-76 and some dynamic memory controllers like core link DMC-620 to high
performance non-blocking interconnects such as the core link CMN-600, AMBA CHI is widely used in networking, mobile and
data centres It also supports high frequency nonblocking data transfers, supports end to end data protection, AMBA 5 includes
AMBA AHB in this version 5 it includes features like secure and nonsecure signalling in address phase and it also supports
more complex systems, it gives improvement to AHB-lite as they have more properties to adopt them widely across different
platforms and provides features like multiple slave select and single and multiple copy which enables scaling in multiple cores
as AMBA 5 has more interconnects it also includes AMBA CXS which is a nonblocking streaming interface protocol which is
used in point to point packetized communications,[9], additionally it also has the AMBA ATP (adaptive traffic profiles) which
is a synthetic traffic framework used for modelling systems and the AMBA distributed translation interface DTIwhich aligns
with the MMU architecture of ARM.
These protocols together work in a microcontroller below figure shows a generic AMBA based microcontroller in which
both AHB and APB buses contribute interconnects to a microcontroller.
Figure 2 : Generic AMBA based microcontroller
From the figure we can see that all the high performing systems in a microcontroller such as ram, rom, processor dma device are
interfaced by AHB the high performing bus, and the low perofrming systems ie: the peripherals in a microcontroller which are
interfaced by APB the low performing bus, there is a bridge which interfaces these both systems here bridge is considered as a
master and the systems are slaves when designing. The above shown high and low performing devices all together contribute a
microcontroller interconnect
C. Overview of AMBA AHB-lite
AMBA AHB - lite is used in high performance synthesizable designs which supports a single master and multiple slaves operation
[4] AHB-lite has many featurs for its high performing, and high clocking frequency systems which include
1) Single clock edge operations
2) Burst transfers
3) Non tristate operation
4) Wide data bus configuration such as 64, 128, 256, 512 and 1024 bits

Master slave configuration of AMBA AHB – lite protocol
Figure 3 : AHB-lite block diagram
Figure 3 shows the block diagram of AHB-lite which has a single master and multiple slaves configuration system. The
interconnect logic of the bus consists of address decoder, slave-to-master multiplexer. The decoder is used to monitor the address
from the master so that required slave is selected and the multiplexer routes the corresponding slave output data back to the master
this is how the operation of AHB-lite takes place
Figure 4: AHB-lite master
Figure 5: AHB-lite slave
Figure 4 indicates AHB-lite master which is responsible for read and write operations in the protocol, it consists of transfer response
signals which maintains transfers across the master and slave , the global signals are the clock and reset as they are carried out in the
entire process hence they are referred as global signals, address and controls are the one which address the transfers and maintains
controllability over the transfers and response, and there are data signals which rolls data in and out of the specified transfers
Figure 5 is a AHB-lite slave which consists same signals as the master but the output of the master is the input to slave, and there
exists a select signal which selects the required slave for the operation

D. Operation
Master sends transfers by driving the control signals and address these signals carry information about the address direction transfer
width they even indicate the transfers which perform burst operation [3]
There can be single transfers also incrementing bursts do not wrap at the address boundaries and the Wrapping bursts which wrap at
a particular address boundaries, Data is moved by the write data bus from the master to slave similarly read data bus is moved from
slave to master every transfer consists of data phase and address phase, considering slave cannot request address phase all the slaves
must be able to sample the address at this time a single slave can request a master which extends the data phase by the signal H-
READY. when the signal is at low it causes wait states to be inserted to the transfer and it also enables the slaves to have some extra
time which is to provide or sample the data, the slave uses H -RESP signal which is used to indicate the failure or success of a
transfer [3]
E. Verification Background
Due to increase in the complexity of the designs and circuits nowadays verification is a must to avoid failure of chips [5]. But how
good is the verification is it efficient or not, there are many methods in verification domain but many industries adopt UVM as their
verification method because of its efficiency and reusable nature [6].
RTL designs and circuits were verified using the same design language ie Verilog language by using test bench, but later on when
the circuit complexity increased these conventional methods were difficult to use as they had many problems like delay mismatch
and slow process, Then later on they proposed a language which can be used for both design and advanced verification called as
System Verilog
System Verilog was introduced for both design and verification, they are more advanced than Verilog language and more flexible
than the hardware description language [7], system Verilog is standardized as IEEE 1800, system Verilog is based on Verilog with
some advancements and extensions it is a evolution to Verilog
System Verilog’s verification environment is flexible and the architecture can be developed on the ideas of the verification engineer
on his basis, all the blocks in the architecture are coded separately and interfaced which is more faster and delay mismatch can be
avoided.
System Verilog in addition supports many features for Verification including concepts like oops, coverage, assertions etc, which
makes it a single language which is suitable for both design and verification. System Verilog is mostly used for design verification
and also the coverage analysis, which we cannot achieve with such efficiency using Verilog HDL [7]. Object oriented feature of
system Verilog makes it a powerful language to verify the corner cases of the logic designs which is not possible using HDL. One
more most important feature of the system Verilog is that it has RANDOMIZE feature using which we can randomize the test
vectors (stimuli) instead of generating all the values, this saves time and has a great efficiency compared to Verilog hence industries
prefer system Verilog for verification.
F. System Verilog Verification Architecture
Figure 6: system Verilog verification architecture

Verification architecture is developed to check the correctness of a design which is under test, by generating stimulus or testbenches
and driving a user defined correct input sequence to the design, which captures the design output and compares with the expected
output. Verification environment is a group of blocks which performs specific operation generating stimulus and driving them to the
respective blocks and also monitoring them. and the classes will be named based on the operation in figure 6 base packet is used to
generate test vectors to generate these test vectors we need variables. all the test bench variables will be generated here in this block
G. Functionality of Blocks in the Verification Architecture
1) Trans Generator: all the variables generated in base packet will be given to TX_GEN here the variables will be converted to
the test vectors
2) Driver: driver drives the test vectors to the respective blocks one to the interface and to the score board
3) Monitor: monitor captures the DUT output and sends it to the SCOREBOARD for verification monitor is for observability
purpose
4) Interface: interface is a communication medium between the test and the designed circuit which is under test (DUT) interface
establishes connectivity, direction, timing, functionality
5) Scoreboard: score board compares the generated test vectors and the DUT to see weather the designed circuit is correct
6) Mailbox: It is a medium which is responsible for transferring of data between blocks the data generated from one block is not
directly transferred to another block rather it is transferred to the mail box from the mail box another blocks takes the data and
processes This operation is done by PUT and GET option
7) DUT: and the DUT output (reference and DUT) and gives the verification result matched or not matched by this system verilog
verification is achieved but system Verilog also has some drawbacks.
H. Issues of System Verilog
System Verilog language is not portable, one developer who works on its verification architecture and a different person wants to
continue should have to learn the architecture framed by that developer ,System Verilog does not have features like reusability
Although system Verilog has some issues industries started developing their own architecture, but one employee who quits and
works for another company has to study their architecture first and get familiarized in which he cannot work instantly. Therefore to
overcome these problems many industries came forward to develop a common universal methodology and the result in which UVM
(universal verification methodology) was introduced.
I. Introduction to UVM
As we know verification contributes about 60 to 70% in VLSI flow all those discussed above methods did not meet the requirements
hence to obtain a fast, reusable, efficient verification UVM was introduced [5]. UVM is not a separate language rather it is a
methodology the language is system Verilog with some additional features and advancements. UVM is a standard verification
methodology to verify integrated circuits [10]. UVM was developed from OVM later upgraded to VMM then further upgraded to
VMM 1.2 and then UVM was introduced, UVM was made a standard by accellera, aldec, cadence, mentor graphics and synopsis
provide support to UVM
Figure : 7 UVM verification environment

Figure 7 shows verification architecture of UVM from the diagram we can see that there are several blocks in the test environment
such as sequence item, sequencer, active, passive agent and a scoreboard and a common interface to link the test design model or the
test vectors to the DUT and perform verification same as the System verilog environment but this environment is a standard
architecture which should be followed by every verification engineers and cannot skip therfore to avoid portable issues . including
UVM is more flexible and have more features than system verilog [6]. From the architecture we can see that there are two diferent
blocks active and passive agent in which active agent maintains input transactions and passive agent maintains output transactions.
hence additionally UVM has two monitors M1 and M2, here sequencer acts as a controller in which it receives response from driver
wether to send data to the driver or not by this we can achieve more controlabilty and efficiency
J. Some Important Components of UVM Verification Architecture Are
1) Library: UVM consists of class libraries which are needed for well constructed reusable environment which improves
interperability and rewriting the IP’s using libraries we can use components to use instantlly.
2) Factory: Commmonly factory is used in oops , object used to instantiating other objects, we can also register objects in this
factory, it also provides variety of create methods and to register to us it with a particular instance
3) Sequence: Sequencer initilazes the verification environment which configures the Verification environment and the DUT, and
the memory is loadd with any types of initial conditions it also registers the settings
4) Scoreboard: Score board is the main component for final results of a verification environment, scoreboard can be implemented
in different way. Scoreboard also takes the inputs and outputs from DUT to determine the result with the reference model and
compares.
5) Agent: DUT may have diferrrent interfaces in which each has different objects associated with them the monitor and
scoreboard or even a PCI interface will be different from the Ethernet interface. Various objects of UVM can be organized as
members of a wrapper class which is known as an agent, there are two types of agents active and passive, active agent
maintains input transactions and passive agents maintains output transactions
6) Driver: Driver is the unit which drives the data from one block ro the respective block , these may be bits of data or information
the drivers duty here is to take the sequence item and provide proper stimulus to the DUT
By all these above mentioned features UVM is more adoped across verification industries in which we can obtain more efficient and
resuable verification to increase productivity.
K. Advantages of UVM over System Verilog
UVM is a fixed architecture in which we cannot change the standard procedure hence the verification environment is protable
UVM is a reusable environment
We can separate the tests from the testbenches hence we can reuse the stimulus
Using factory feature we can simpilify and modify components easily
UVM helps to configure the mechanisms of different testbench components based on the use of which verification environment is
used
UVM is also simulator independent ie : it is is supported by all the simulators and not dependent on any particular simulator.
III. COMPARASION
A. AMBA comparison
Figure 8: Comparison of AMBA

AMBA has introduced its first bus in 1995 and its AMBA 5 the latest version in 2013, AMBA protocols has gained a wide
popularity and standards in industries they are used in many interconnects and SOC designs Figure 8 shows various types of AMBA
protocols based on their AMBA family and their year of introduction. All these protocols are classified based on their operating
nature, performance, clocking, transfers etc, In addition there are more new protocols like CXS which is a non blocking streaming
interface protocol, The AMBA Distributed Translation Interface the DTI which aligns with the architecture of MNU of the
ARM which is suitable for scalable distributed messaging protocol, The AMBA LTI Local Translation Interface ie: LTI
protocol specification which aligns with the Arm MMU system architecture which provides higher performance and
achieves efficient translation services. And the LPI protocol which has Q channel and P channel to manage clock and
power [9]. By all these factors AMBA protocols have been classified.
B. Verification Comparison
Verilog vs System Verilog
On the other hand let us compare system Verilog verification and UVM
IV. CONCLUSION
This paper shows the different versions of AMBA protocols their nature of operation and their contribution to microcontrollers, and
we have discussed about AMBA AHB-lite in detail and their working. and as we know complexity of VLSI chips and their logic is
increasing very rapidly we need a fast reliable and efficient verification of designs so we have discussed need of verification its
evolution and about system Verilog and UVM and compared them based on their various features.

REFERENCES
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[2] Milica Mitić and Mile Stojčev “A Survey of Three System-on-Chip Buses AMBA CoreConnect and Wishbone” university of Niš
[3] Sravya Kante, Hari KishoreKakarla and Avinash Yadlapati “Design and Verification of AMBA AHBLite protocol using Verilog HDL” , Vol 8 No 2 Apr-May
2016, e-ISSN: 0975-4024 International Journal of Engineering and Technology (IJET)
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[7] Jonathan Bromley Verilab Ltd , Edinburgh Scotland If SystemVerilog Is So Good, Why Do We Need the UVM.
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[9] www.arm.com
[10] www.wikipedia.com

A Review On AMBA AHB Lite Protocol And Verification Using UVM Methodology

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