Optics and Photonics Journal, 2013, 3, 112-117
doi:10.4236/opj.2013.32B028 Published Online June 2013 (http://www.scirp.org/journal/opj)
System-on-a-Chip (SoC) Based Hardware Acceleration
for Video Codec
Xinwei Niu, Jeffrey Fan
Department of Electrical and Computer Engineering, Florida International University, Miami, USA
Email: xinwei.niu@fiu.edu, Jeffrey.Fan@fiu.edu
Received 2013
Nowadays, from home monitoring to large airport security, a lot of digital video surveillance systems have been used.
Digital surveillance system usually requires streaming video pro cessing abilities. As an advanced v ideo cod ing method,
H.264 is introduced to reduce the large video data dramatically (usually by 70X or more). However, computational
overhead occurs when coding and decoding H.264 video. In this paper, a System-on-a-Chip (SoC) based hardware ac-
celeration solution for video codec is proposed, which can also be used for other software applications. The characteris-
tics of the video codec are analyzed by using the profiling tool. The Hadamard function, which is the bottleneck of
H.264, is identified not only by execution time but also another two attributes, such as cycle per loop and loop round.
The Co-processor approach is applied to accelerate the Hadamard function by transforming it to hardware. Performance
improvement, resource costs and energy consumption are compared and analyzed. Experimental results indicate that
76.5% energy deduction and 8.09X speedup can be reached after balancing these three key factors.
Keywords: SoC; Software Profiling; Hardware Acceleration; Video Codec
1. Introduction
System-on-a-Chip (SoC) refers to integrating all compo-
nents of a computer or other electronic systems into a
single integrated circuit (chip). The SoC designer’s role
is to integrate all the parts into a chip to implement so-
phisticated functions in a relatively short time [1]. To-
day’s computer system is much more complicated and
powerful than those in 1990s. Obviously, the old
MPEG-2 standard is not an efficient video standard any
more for the novel technology. That is why there is a
new video coding standard, called H.264/MPEG-4 Part
10 Advanced Vi deo Coding (AVC) or just H.264 [2] .
The increased customer demands for advanced SoC
devices result in shorter design cycle and time-to-market
schedule. There is a demand that the final product should
have the optimized partition of hardware and software.
Profiling plays an important role because it determines
the bottleneck of the whole system. It is helpful for de-
signers to keep the balance between the hardware and the
software. Thus, better overall system performance with
little overhead can be achieved [3].
Hardware acceleration has trade-offs. Implementing
the whole algorithm on hardware is time saving but with
less flexibility. General purpose hardware provides great
flexibility but it is time-consuming for software applica-
tion. So it is importan t to balance the trade-offs of a sys-
tem when constructing a hardware accelerator.
There are several previous researches about the soft-
ware profiling and hardware acceleration for video codec.
It was found that hotspot functions can be chosen based
on the execution time [4,5]. Some authors said the hot-
spot functions can be identified by monitoring the loop
rounds [6,7]. However, their methods are not accurate
enough to identify the hotspot functions. Functions with
high execution time or loop rounds cannot be viewed as
the most suitable candidates for hardware acceleration. A
general hardware acceleration approach was presented by
Chen et al. [8]. They used the pipeline to accelerate the
system, but their hardware accelerator was connected to
the system bus, so that the processing time might be in-
fluenced if other peripherals would like to communicate
with processor at the same time. Besides, the function
they choose is not the real hotspot function in H.264.
Kordasiewicz et al. showed the speed and area optimiza-
tions for H.264 Discrete Cosine Transform (DCT) and
quantization blocks [9], but DCT may not be the most
suitable function to be accelerated in H.264. Elgato [10]
has a USB thumb disk that acts as an H.264 hardware
accelerator. Even though the USB 2.0 bus processes
about 25 MB/s - 30 MB/s of bandwidth, the bandwidth of
Northbridge can take up to 2132 MB/s, which is about
700 times faster than the USB bus as a peripheral bus.
Not to mention that if we implement the chip into the
Northbridge, it will bring a lot of compatibil ity problems
Copyright © 2013 SciRes. OPJ
X. W. NIU, J. FAN 113
too. H. C. Lin et al. [11] used DSP to accelerate the H.264
codec. However, the DSP is not as flexible as FPGA, and
it is not inherently design ed for parallel computing.
Therefore, in this work, a software profiling method
for H.264 encoder is presented in order to find the bot-
tleneck. The hotspot function is transformed into hard-
ware and optimized for further hardware acceleration.
The Co-processor based SoC architecture is designed and
The remainder of this paper is organized as follows. In
Section 2, an overview of H.264, software profiling tools,
and hardware acceleration are presented. The proposed
software profiling method and hardware acceleration
architecture are introduced in Section 3. And in Section 4,
experimental results are presented. The conclusion and
future work are given in Section 5.
2. Background
In H.264, video source is compressed to a small size
while the quality is kept at an acceptable level. Video
signals have two significant types of red undancy, namely,
time-domain redundancy and spatial domain redundancy.
H.264 standard compresses media in Macro Blocks
(MBs). One MB is a 116 pixel block. When the
process starts, H.264 encoder separates the current video
frame into numerous 16 ×16 MBs and the MBs are
processed one by one.
There is a very important module called Motion Esti-
mation (ME) in time redundancy removing phase [12].
After splitting frames, MBs from current and several pre-
vious frames are sent to the ME module. A lot of compu-
tation and self-analysis processes occur in this module,
then the closest MB within the previous frames, which
can be used to represent current MB, is found by the ME
module. In spatial redundancy removing phase, Discrete
Cosine Transform (DCT) is used as a key component to
differentiate the high/low frequency parameters of the
residue of an MB [13].
Software analysis platforms attract the resear ch in terests
for years. As shown in Figure 1, there are several types of
profiling methods, such as software based methods (SBP),
hardware based methods (HBP) and FPGA based meth-
ods (FPGABP) [14].
Software based profiling (SBP) tools are mostly used
for evaluating the characteristics of software applications.
Virtual simulation is one way to profile software applica-
tions. On the other hand, Instrumenting code insertion
will insert instrumentation code to fetch the p erformance
data of the running CPU, and read the number of pro-
gram counters (PCs) to collect the exact number of the
called functions [15].
Hardware based profiling (HBP) tools can be used to
monitor the software behavior on advanced processors.
These kinds of hardware counters aim for some specific
Figure 1. Profiling methods category.
events. It is better to use hardware counters rather than
revising the application code. The other benefit is this
kind of counters adds little performance overhead be-
cause the data is collected during run-time.
FPGA based profiling too ls (FPGABP) can be used to
profile software running on FPGA based SoC system [16].
The on-chip profiling hardware gathers all the needed d a ta
when the application executes on the soft-core processor.
These tools can keep the latency and performance over-
head at a minimum level.
Hardware accelerators are used to implement dedi-
cated function for nearly forty years. Notable perform-
ance improvements can be obtained by using hardware
accelerators [17]. There are three main hardware accel-
eration methods.
Directly implement multiple instructions at the same
time to improve the performance.
Connect the designed hardware accelerator to the
processor via a system bus.
Implement the hardware acceleration part as a co-
3. System Architecture
3.1. Software Profiling
Normally, hotspot functions consume a substantial
amount of execution time for the specific algorithm. This
makes them have a high probability to be used for run-
time optimization. Traditionally, the function, which
costs most execution time, is viewed as the hotspot func-
tion. However, after taking a deep look at the application
and its internal functions, an attribute called cycle per
loop is viewed as a critical factor besides the execution
time. If the function has only one loop and need only a
few cycles to finish, the function is pretty easy to execute
for the CPU. It may not have intensive computational
steps, and there may not be significant differences if the
function is transformed to the corresponding hardware.
Even though the function is transformed to the hardware,
and the function loops a lot of rounds and costs lots of
Copyright © 2013 SciRes. OPJ
execution time, the CPU may not gain performance im-
provement. On the other side, if the function costs a lot
of cycles to finish, then the function may not be able to
be easily transformed to hardware. Moreover, what if this
function only executes few rounds in the software applica-
tion? It can be a waste of hardware resource for the SoC.
From this point, execution time shouldn’t be the only
aspect to consider in the profiling method. Instead, two
additional attributes called cycle per loop and loop round
are also important for profiling the software.
As shown in Figure 2, the x-axis stands for the loop
round of software application while th e y-axis represents
cycles per loop. Points on the figure stand for the corre-
sponding software functions. It is shown that the point B
is a function which has the lowest priority to be trans-
formed into hardware. It has low cycles per loop and low
loop rounds, so as to the execution time. For functions
with higher cycles per loop but lower loop rounds. For
example, the intensive data accessing functions. Hardware
may not have significant improvements for these kinds of
functions, because the majority of their execution time is
waiting time. The SearchWindow in H.264 is this type of
function. These kinds of functions are located in the area
where point A is. Another concern is higher loop rounds
and lower cycles per loop scenario. For example, a func-
tion just reverses the value of a signal. Even the function
can loop millions of times, and has a long execu tion time,
it is not suitable to be accelerated because there is little
difference between software and hardware approaches.
These kinds of functions are located around the area
where point C is. Obviously, the target hotspot functions
should not only have longer execution time but also
higher loop rounds and cycles per loop. These functions
are located around the area D. Functions in area D should
have higher priority to be viewed as candidates for
hardware acceleration. The transformed functions can
greatly reduce the burden for the embedded processor
and improve the system performance.
Figure 2. Proposed profiling theory.
3.2. Hardware Acceleration
The hardware system architecture is shown in Figure 3.
Xilinx Virtex 5 FPGA board is used as the SoC platform
[18]. In our SoC system, the CPU frequency is 50MHz in
order to guarantee every Hadamard IP works smoothly.
The MicroBlaze has its Local Memory Block RAM
(BRAM), which can be configured at maximum 64 KB.
BRAM can be accessed through the Local Memory Bus
(LMB) [19] by two separate interfaces. Both of ILMB
and DLMB are 32 bit bus and can be accessed by the
MicroBlaze in one clock cycle.
There is an on-chip system bus called Processor Local
Bus (PLB) [20] to communicate with other peripherals,
such as DSP IP, serial connection IP and other custom-
ized IPs. Xilinx provid es another kind o f connection way
called Fast Simplex Link (FSL) [21]. FSL is a uni-direc-
tional point-to-point interface. The MicroBlaze can have
up to 16 pairs of FSLs. Each pair of FSL has one input
and one output channel. The data, which will be proc-
essed, can be transmitted between the MicroBlaze and
customized IP immediately.
Speed, energy consumption and resource costs are
three major concerns for modern system development.
Designers must balance the trade-offs of these three fac-
tors. After installation of the customized IP, energy con-
sumption of the whole system with/without the IP is
measured. System with IP consumes more power than
the system without the IP because the extra IP costs more
Figure 3. SoC Architecture based on microblaze.
Copyright © 2013 SciRes. OPJ
X. W. NIU, J. FAN 115
transistors. If the system with customized IP spends
much less time than the system without customized IP
when executing the same amount of da ta, the total en erg y
consumption can be reduced. Usually, energy consump-
tion’s threshold depends on the system requirements. If
the energy consumption cannot meet the requirement, the
whole hardware IP must be optimized again. In this sce-
nario, the designer must pay attention to the hardware IP
and use some optimization methods to lower the energy
consumption. Designers must balance the trade-offs of
system speed, energy consumption and resource costs to
find an optim ized design.
4. Experimental Results
In this research, a new way to find the system overhead
caused by software applications is proposed. H.264 video
codec is chosen to be our experimental target but not
confined to it. The whole workflow fits all the design
processes involving hardware-software co-design. This
method provides a guideline to achieve a quick evalua-
tion of the software partition.
The official C model of H.264 (called “JM”) is used to
set up the H.264 environment. First, a sequence of un-
compressed YUV frames is prepared [22]. Second, a
configuration file that contains the right format and in-
formation of the YUV frames is prepared. The configu-
ration file includes the essential constraints of the com-
pressed method. Third, the H.264 encoder source code is
built into an executable file. The profiling tool-Intel
VTune performance analyzer [23] is used to monitor the
running software. All the software statistics are gathered
through run- time profiling.
Figure 4 is the normalized statistics of the profiled
H.264 information. As mentioned before, a function,
which has high cycles per loop and loop rounds, should
be the aimed hotspot function besides the execu tion time.
On one hand, even though the function like iabs has high
execution time and higher loop rounds, it only costs few
Figure 4. Normalized statistics of H.264 encoding.
numbers of cycles per loop. In this case, it may not suit-
able for acceleration. In addition, the function of iabs is
going to get the absolute value of the input data. When
the iabs is transformed to a hardware IP, the system may
not have significant performance improvement. On the
other hand, SetupFastFullPelSearch function has higher
cycles per loop number, but it costs relatively low er loop
rounds. Besides, transferring searching function into
hardware may not benefit the system performance a lot.
It is not a calculation intensive function. Thus, it is not
the first priority as well. The Hadamard transformation
has intensive data calculation, higher cycles per loop and
loop rounds. With higher execution time, it is suitable to
be our candidate to be accelerated, so it will be the first
priority for further optimizatio n.
The Hadamard transformation is a generalized Fourier
transforms. It performs symmetric, involution, linear
operation on 2m Real numbers. The Hadamard transform
Hm is a Matrix, which is a square array of plus and minus
ones whose rows are orthogonal to the others. If H is a N
× N Hadamard matrix, then the product of H and its
transpose is an identity matrix. A Hadamard matrix can
only exist for n is 1, 2, or multiple of 4, matrix I is an
identity matrix [24].
In order to find the optimal solution for aimed SoC
architecture, four typical types of Hadamard accelerators
are provided. Different performance data will be evalu-
ated based on the Virtex 5 FPGA board.
The original Hadamard transformation using wire
connection, which directly connects different signals to
the outputs. Named Hadamard_1.
Different from the original way, each step of the
Hadamard calculation is stored in a registers to get the
output val ue. Name d Hadamard_2.
The fast Hadamard transformation is used for hard-
ware acceleration. Signals are directly connected together
to the outputs. Named Hadam ard_3.
For three-layer fast Hadamard transformation, mul-
tiple registers are used to store the results of each layer.
Called three-layer pipeline Hadamard_4.
The designed co-processor SoC system uses FSLs for
communications. The software codes are executed in the
MicroBlaze processor, but the chosen Hadamard function
is replaced by the corresponding hardware IP. This is
achieved by routing the data through FSL to IP, and
sending the results back to the processor. Figure 5 shows
the design cost of different Hadamard IPs. Data can di-
rectly be read that Hadamard_2 costs the most on-chip
resource, then following Hadamard_1 IP. Because Ha-
damard_2 uses register every processing step, it costs the
most D Flip-Flops and other resources. Hadamard_1 di-
rectly connects signals together to the outputs, so it
Copyright © 2013 SciRes. OPJ
doesn’t need D Flip-Flop. Hadamard_3 is the fast Ha-
damard transformation, and it also directly connects sig-
nals to the outputs, so Hadamard_3 cost zero D Flip-Flop.
Hadamard_3 and Hadamard_4 cost nearly the same
amount of multiplexers and XOR gates. Hadamard_1 and
Hadamard_2 cost more multiplexers and XOR gates.
Figure 6 is the comparison of the system speedup
based on the co-processor design. The average speedup
of four types of hardware accelerators is 7.9X. Ha-
damard_1 and Hadamard_3 can reach the highest
speedup of 8.09X. Among these designs, the speedup of
Hadamard_2 is the lowest, because it uses more hard-
ware resources to build the hardware accelerator. It uses
register every step when finishing the data calculation.
Hadamard_1 and Hadamard_3 have the same speedup
because both designs use wires to directly connect the
signals together to get output results. In the hardware
design, when designers use wire to connect two signals
together, the result is generated immediately. Ha-
damard_4 is a three-layer pipeline design. It uses regis-
ters to store the intermediate results. Hadamard_4 costs
longer time to finish the algorithm for the first data set,
after that, it generates data every clock cycle.
Figure 7 is the saved energy of Co-processor design.
The hardware energy consumption is compared to the
pure software method. Among the four types of hardware
Figure 5. Design Cost of Different Hadamard IPs.
Figure 6. Speedup of Different Hadamard IPs.
Figure 7. Saved Energy of Different Hadamard IPs.
accelerators, Hadamard_2 uses the most on-chip re-
sources. Obviously, Hadamard_2 costs the most energy.
Hadamard_1 and Hadamard_3 use little power when the
algorithm is running on the system, so both of them cost
the least energy. They can save 76.52% energy when
compared to the pure software method. Because Ha-
damard_4 uses registers to store the intermediate results,
it costs more energy than Hadamard_1 and Hadamard_3.
Even Hadamard_1 and Hadamard_3 have the same
speedup they also save the same amount of energy for
this specific algorithm. However, based on our experi-
mental results, Hadamard_1 costs more on-chip re-
sources than Hadamard_3, so Hadamard_3 is a better
choice to accelerate the video codec application.
The software profiling method is more accurate com-
pared to the former ones which use a single indicator
such as executio n time or loop ro und [4 -7 ]. Kor dasiew icz
et al. accelerate the video codec through DCT, which is
not the significant hotspot in H.264 [9]. As for the hard-
ware acceleration, it can get a balanced system which has
not only higher performance but also low resource costs
and energy consumption. Authors in [8] use the system
bus, which may not get the same performance improve-
ment as co-processor design. DSP solution is to acceler-
ate the video codec [11]. However, the DSP is not as
flexible as FPGA.
5. Conclusions
In this paper, a hardware acceleration method to improve
the performance of software application is introduced.
Even H.264 is used as our target software application,
but our hardware acceleration workflow will not be lim-
ited to H.264. The software method can be used to iden-
tify the hotspot function. Besides of the execution time,
two-dimensional attributes called cycles per loop and
loop rounds for the internal functions of software appli-
cation are introduced. After analyzing the profiling re-
sults of H.264, the Hadamard fun ction is identified as the
hotspot function. Different hardware accelerators based
Copyright © 2013 SciRes. OPJ
Copyright © 2013 SciRes. OPJ
on the hotspot function are designed and mapped as a
co-processor. Experimental results show the fast Ha-
damard transformation is a better candidate for hardware
acceleration. It costs less on-chip resources, saves 76.52%
energy and achieves an 8.09X speedup compared to the
pure software method. FPGA based software profiling
platform will be setup in the future to eliminate draw-
backs of hardware based profiling tools. System behavior
using off-chip memory for data storage will also be stud-
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