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Hardware programming for software developers:
Several disrupting
factors in the traditional microprocessors being the chip of choice for C-Programming algorithms.
These include cost and
accessibility of cross-compilation tools, the processing power, the speed
limitations of microprocessors, and the availability of more reliable
building blocks.
These are three university
individual researchers breaking down the problem into understandable laymen step-by-step the
average developer can follow to determine if FPGAs are worth the
bother.
This is based on hundreds of hours of class and lab testing.
These authors
are willing to share their instructional materials, curricula, and advice for the readers here.
Problem identification:
Microprocessors continue to represent the largest "bang for
the buck" and are at the center of most systems.
FPGAs are semi-custom, co-processing resource that is "picking off"
the parallelization tasks from CPUs. FPGAs do this – at lower clock
speeds and power – by deploying multi-core parallelism.</p>
HPRC:
High Performance Reconfigurable Computing (HPRC) as a branch of Computer
Science is thriving.
HPRC Largely driven by GPGPU (general-purpose graphics
processing unit) growth, HPRC is also supported by FPGA-based
applications.
The programming environment is considered to be the main
obstacle preventing FPGAs from being used to their full potential in
accelerators. Thus, the need to gain familiarity with High Level
Languages (HLLs) is inevitable.
A high-level language (HLL) is a programming language such as C, FORTRAN, or Pascal that enables a programmer to write programs that are more or less independent of a particular type of computer. Such languages are considered high-level because they are closer to human languages and further from machine languages.
Architectural differences in C for FPGAs vs. C for CPUs:
The
C language that is refactored for FPGA, can be characterized as a
stream-oriented programming language, and process-based language.
Processes are organized into main building
blocks interconnected using streams to form the architecture for the
desired hardware module.
From a hardware perspective, processes and
streams are hardware modules and FIFOs (First In, First Out registers)
respectively.
The C programming model is generally based on the
Communicating Sequential Processes model.
Every process must be
classified as a hardware or a software process. It is the programmer's
responsibility to ensure inter-process synchronization.
Like all human readable HLLs, C
does not provide access to the clock signal, which relieves the
designer from implementing cycle synchronization procedures.
Understand, it
is possible to attach HDL modules and synchronize them at the RTL, (Real Time Level), using clock signals. It is worth noting that C as a hardware
design language does not permit dynamic resource allocation (e.g.,
"malloc()" and "calloc()").
The second unique language
construct, besides being process-oriented, is stream orientation.
Streams are unidirectional and can interconnect only two processes,
which imposes restrictions on hardware module architectures designed in
C.
Since pipelines can become a source of deadlocks, the designer
particularly needs to consider mechanisms to avoid them. Unfortunately,
occurrences of deadlocks are difficult to trace during simulations
since the "#pragma co pipeline" C-to-HDL compiler directive is ignored
during software simulation.
These problems are usually revealed after
implementation when the module is tested in hardware.
In
addition to streams and processes, C as a design method provides
signals and semaphores. These structures are used for inter-process
synchronization. The best practice is often to implement pure pipeline
modules, with the lowest possible number of synchronization signals.
Software processes are converted to multiple streaming hardware processes where they use streams, signals, or memory for synchronization.
Methodology:
HLLs are
used for purposes of data type flexibility in terms of HDL module integration use.
Typically, there
will be a range of data structures available such as co_int2, co_int32,
co_uint1, co_uint32, etc.
These constructs are also a source of
inconsistency between the software and hardware implementations.
Prior
to FPGA implementation, all hardware modules should be simulated
on a GPP (general purpose processor) where their data structures are
mapped on the types available on the GPP.
Unfortunately GPPs use limited
sets of data types, so each time a simulation is performed, the data
is extended to the nearest wider data type, which affects intrinsic
computation precision.
This occurs unless a dedicated
macro is used (e.g. "UADD4()" and "UDIV20()"); thus, using macros is
encouraged.
Special attention must be paid to
functions, since they highly simplify modular implementation, since this is the
common design strategy.
The following pragmas are useful: "co inline,"
"co implementation," "co unroll," "co pipeline," and "co set."
These
allow module shaping, providing a set of restrictions. By example,
using "inline" in a function body enables the compiler to freely modify
the internal architecture of the module.
if not implimented, the function is
treated as a uniform module, which cannot be modified by the compiler.
Static recurrence is permitted and proves to be a useful structure in
many applications such as a binary tree implementation with the
"add_tree()" command is needed.
The limitations of using C for
hardware result mostly from the exceptions of the adaptation of ANSI C
to hardware design. Notable examples include:
Lack of dynamic recurrence
No support for unions
Dynamic memory allocation is unsupported (free(), malloc()) in hardware
Limited support of pointers
A pointer may only point to one block of memory
Pointers must be determined at compilation time
Several techniques to optimize
performance of the implemented hardware modules that may work.
Reading and writing to
streams can be implemented in several ways and one is to
provide an efficiant pipeline performance (1 cycle per single operation).
Data access conflicts may also contribute to significant reduction of expected performance. A solutions, is important to debug such conflicts by memory duplication or multi-object-optimization by table scalarization
(using the "co_array_config()" instruction).
The number of combination logic levels should be kept reasonably low, which can be
achieved with a single pragma parameter (e.g., "co set Stage Delay
32").
Stage Delay Analysis provides the tools needed to see how decisions made in C algorithms will propagate in logic and clock cycles.
As a general rule, it is recommended to use appropriate data structures to
maximize data throughput.
The C-to-FGPA IDE delivers a range of tools
which facilitate flexable debugging.
One convenient tool is the Stage Master
Explorer (SME), which may be used to examine code and pinpoint
throughput bottlenecks.
The measured performance in the SME is expressed
through a set of four parameters, which characterize the digital
module: Latency, Rate, Max. Unit Delay, and Effective Rate.
Two simple teaching examples:
1.) Implementation of an FPGA-accelerated HASH function using C: In
this exercise exampled below, the programmer's, task was to implement a hash function in
C.
The algorithm could not be implemented in a naive way (by copying
and pasting it inside the hardware main function body), but it had to
be re-coded and optimized as hardware.
The first step was to run a
given hash function on a GPP to produce a reference output for the
given input.
The reference code in ANSI-C is shown below.
Every student-programmer
had this same input vector, but different functions, preventing
plagiarism. Such solutions have the additional advantage of verifying
if the whole solution is correct.
To do so, a programmer must only check the
correctness of one output number.
Noted that the interface between the CPU and FPGA is 32 bits wide, and
equates to four-bytes of data is transferred at once to the
hardware module to minimize bottleneck via system
throughput.
The programmers results differed in quality, but the best ones
used pipelined operations, which resulted in a high throughput with
slightly higher latency than for non-pipelined cases programming solutions.
A few student-programmers
unrolled an internal for loop using the pragma "CO UNROLL" directive.
By using pipelined operations, they reduced the hashing function execution time N times and increased output N times.
The disadvantage of such an approach was the high usage of available
logic resources for high over-all data-flow.
#2 A Prime Number Generator using C:
Another
tutorial began by asking student-programmers to find algorithms in literature
used as Prime Number Generators (PNGs).
This knowledge was used during
the following hands-on exercises.
The students also had to write their
own module(s) in VHDL, which were used in the PNG.
The module could be a
trivial one but – if so – the number had to be greater than one (e.g.,
the operation of square and incrementation by constant factor).
The
modules had to be 100% compatible with the C external module standards
and verified as accurate in a test-bench.
The students got their
guidelines about the communication interface connecting the CPU and FPGA
(using a 32-bit bus) and software design was a user
interface that collects information regarding the lower and upper bounds
between which the prime numbers had to be found.
This information had
to be sent to the hardware module using a stream, after which the
hardware process started to run. The algorithms selected by student-programmers
generated proper primes and sent them to the software application, whose
role was to present these results on-screen and write them into a text
file.
PNG was used as an example for two reasons:
It is hard to write such a function in pure VHDL, which makes the advantages of C more visible
Every algorithm that can be used to generate primes is composed of
many operations. Therefore it is easier to pick one and implement it in
VHDL, avoiding duplication across students within the same group.
Some students decided to implement PNG in naive way
using algorithms called trial division; that is, by checking if a
number can be divided, without a remainder, only by itself. As a
"reward," they had to implement some "nasty" operation in VHDL, like a
modulus or a square root. Many students decided to use the Sieve of
Eratosthenes; a few students decided to use the "Fermat's 4k+1" and
"Euler's 6k+1" algorithms to check if a number is a prime. The best
method was one proposed by student Grzegorz Glowka BSc due to its
adaptation of all three previously mentioned algorithms. Student Glowka
observed that -- in some intervals -- some methods are more efficient
than others, and he implemented his PNG in such a manner as to leverage
this fact.
The lessons from the exercise were as follows:
Implement everything in C and perform software simulations, then
run working applications and tests that measure their performance in
the hardware
Find weaknesses of C-to-HDL translation and eliminate them by
replacing them with regards to HDL blocks. Regenerate the whole design,
implement it in hardware, and then run tests and measure their
performance.
Consider rewriting key elements in HDL to tune performance.
Rewrite the whole hardware part into HDL, or only those parts that
are responsible for data processing, leaving C to interface and
transmit data, etc.
Results:
Since we are teachers, our students
are our "results."
We are happy to report that both their grades were
up (from prior years of similar coursework) and that students felt a
little more prepared for corporate life with more hands-on method of approach.
The class continues to
develop as the institution frame-work provides.
Acknowledgments:
The authors would like to acknowledge the assistance given by Brian Durwood of Impulse Accelerated Technologies in the preparation of this article.
About the authorsGrzegorz Gancarczyk
was born in Nowy Sacz, Poland, in 1984. He received an MSc degree in
the field of electronics from the AGH University of Science and
Technology (AGH-UST), Krakow, Poland, in 2009.
Since
2009, he is with the Academic Computer Centre (ACC) CYFRONET AGH,
Krakow, Poland and now also with the Department of Electronics,
AGH-UST, Krakow, Poland. His research interests include engineering
education, statistics, stochastic processes, phenomenon of noise,
digital signal processing and hardware acceleration of numerical
methods. You can contact Grzegorz at gegula@agh.edu.pl
Maciej Wielgosz
was born in Krakow, Poland, in 1979. He received his MSc and PhD
degrees in the field of electronics from the AGH-UST, Krakow, Poland, in
2005 and 2010, respectively.
Since 2005, he is with
the ACC CYFRONET AGH, Krakow, Poland and since 2009 also with the Dept.
of Electr., AGH-UST, Krakow, Poland. He has published over 40 papers
in journals and conferences and also one book: "FPGA implementation of
the selected floating point operations" (Warszawa: Akademicka Oficyna
Wydawnicza EXIT, 2010). His research interests include educational
issues in electronics, data compression, neural networks and hardware
acceleration of computations. You can contact Maciej at wielgosz@agh.edu.pl
Kazimierz Wiatr
was born in Tarnow, Poland, in 1955. He received MSc and PhD degrees in
the field of electrical engineering from the AGH-UST, Krakow, Poland,
in 1980 and 1987, respectively, D. Hab. (habilitation) degree in
electronics from the University of Technology of Lodz, Lodz, Poland, in
1999. Professor degree in 2002.
Since 1980, he works
at the Dept. of Electr., AGH-UST, Krakow, Poland. Head of
Reconfigurable Computing Systems Group. Since 2004 director of the ACC
CYFRONET AGH. Since 2006 chairman of the board of PIONIER - Polish
Optical Internet - Consortium. Between 1998 and 2002 adviser to the
Prime Minister of Poland on "educational and upbringing of the young
generation".
Managed 9 Polish Scientific Research Committee research
grants. His works resulted in over 200 publications, 19 books, 5
patents and 35 industrial implementations.
Achieved Polish Science and
Higher Education Minister's Award. Has been involved with youth
education for more than 30 years. One of the founders of the Polish
independent scouting movement. His research interests include
educational issues, processes automation, image systems, multiprocessor
and many core systems, reconfigurable devices and hardware methods of
calculations accelerating.
Prof. Wiatr was appointed
in 2007 to a chairman of Tarnow Scientific Society. Member of the
Polish Information Processing Society, European Organization for
Information and Microelectronics (EUROMICRO). In the Sixth and Seventh
Term Senate was a chairman of the Science, Educational and Sport
Committee.
Reviewer in the IEEE Expert Magazine, IEE Computer and
Digital Techniques, IEE Electronic Letters, IEEE Transactions on Neural
Networks, Eurasip Journal on Applied Signal Processing, Journal
Machine Graphics and Vision. Prof. Wiatr can be contacted at wiatr@agh.edu.pl
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A hard fork (or hardfork) is a permanent divergence in the blockchain, which occurs when non-upgraded nodes can’t validate blocks created by, (already), upgraded nodes that follow newer consensus rules.
The Cryptocurrencies after hard fork share a transaction history up to a certain time and date.
The first intentional hard fork splitting bitcoin happened on 1 August 2017, resulting in the creation of Bitcoin Cash.
Other coin split created altcoins such as Bitcoin Gold
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owner wants to claim his, it has to be implemented in the wallet.
Trezor Wallet implemented is a tools for Bitcoin Cash as well as for Bitcoin Gold(BCH,BTG) whereby to claim these coins for users who owned Bitcoin funds on addresses when these hard forks happened.
In November 2018, a hard-fork chain split of Bitcoin Cash
occurred.
This hard-fork resulted in the creation of Bitcoin ABC and
Bitcoin SV.
See also :
The number of users of non-deterministic wallets is currently
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The legacy of Non-Deterministic wallet and HD wallet combined resolves into flexibility for end-user with interoperability and enhanced privacy with one-time backup.
HD wallets solve problems of legacy cryptocurrency wallets which
randomly generate private keys on the fly and require repeated backups; insanity!
HD wallets bring the possibility of deriving all the addresses (public
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The advantages of
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Easy backups - if you control the recovery seed, you can generate the entire tree of children keys (public/private key pairs).
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