=Paper=
{{Paper
|id=Vol-1844/10000654
|storemode=property
|title=Improving of a Circuit Checkability and Trustworthiness of Data
Processing Results in LUT-based FPGA Components of Safety-Related Systems
|pdfUrl=https://ceur-ws.org/Vol-1844/10000654.pdf
|volume=Vol-1844
|authors=Oleksandr Drozd,Miroslav Drozd,Oleksandr Martynyuk,Mykola Kuznietsov
|dblpUrl=https://dblp.org/rec/conf/icteri/DrozdDMK17
}}
==Improving of a Circuit Checkability and Trustworthiness of Data
Processing Results in LUT-based FPGA Components of Safety-Related Systems==
https://ceur-ws.org/Vol-1844/10000654.pdf
Improving of a Circuit Checkability and
Trustworthiness of Data Processing Results in LUT-
based FPGA Components of Safety-Related Systems
Oleksandr Drozd, Miroslav Drozd, Oleksandr Martynyuk, Mykola Kuznietsov
Institute of Computer Systems, Odessa National Polytechnic University,
ave Shevchenko 1, 65044 Odessa, Ukraine
drozd@ukr.net, miroslav_dr@mail.ru, anmartynyuk@ukr.net,
koliaodessa@mail.ru
Abstract. The possibility of improving on attributes of a solution which are tra-
ditionally opposed each other is proved. For digital components of safety-
related systems, the method of improving on attributes of a checkability of the
circuit and trustworthiness of the results calculated on FPGA with the LUT-
oriented architecture is offered. The method is directed to improving of the
ready project by a choice of the version of a program code without change of
the hardware decision. Versions of LUT memory programming and a set of
faults on which these versions exert impact are generated. Faults of shorts be-
tween adjacent address inputs of LUT are considered. Operation of the circuit is
simulated on all versions and on all set of faults. The method selects the ver-
sions providing increase in a checkability of the circuit in a normal mode and
trustworthiness of results in emergency mode of the safety-related systems.
Keywords: safety-related system, digital component, FPGA, LUT-oriented ar-
chitecture, checkability of the circuit, trustworthiness of the results
Key terms: HighPerformanceComputing, ConcurrentComputation, Model,
Method, Simulation
1 Introduction
Objects of the increased risk in power engineering, on transport and other areas became
natural surroundings of the human. Power stations and the high-speed railroad, aircraft
permanently increase complexity and capacities. It requires the appropriate enhance-
ment of the safety-related systems ensuring the functional safety of these objects [1, 2].
We offer a method for improving the digital components of safety-related systems
in two attributes important for the functional safety: checkability of the circuit and
trustworthiness of results. The insufficient checkability of the circuit restricts possibili-
ties of on-line testing to detect faults in the course of computation. This creates a prob-
lem of the hidden faults in safety-related systems [3, 4]. Trustworthiness of results plays
a crucial role for accident prevention and lowering of their consequences. Both attrib-
utes are traditionally opposed each other, i.e. improving of one attribute will be
reached due to deterioration in another. The high ckeckability of the digital circuit
reduces trustworthiness of result as promotes frequent manifestation of faults in the
form of errors. The low checkability of the circuit increases trustworthiness of results
as it masks faults better. High trustworthiness of results is provided by development
of fault-tolerant circuits [5], structural redundancy of which reduces a checkability.
Such opposition of these and other attributes is perceived as a norm, however it
has no objective character, and it is only result of limitation of our models, i.e. our ideas
concerning the nature of objects of a research. A certain step in development of models
can be taken, using resource-based approach [6, 7]. According to this approach, the
human develops models, methods and means, component resources, from simple to
real, by passing in the consciousness the levels of resources development: replication,
diversification and autonomy. Simple forms of resources are exact and sequential
according to initial representations and opportunities of the human. Real resources
reflect the natural world in which information technologies most show two features:
parallelism and fuzziness. All history of development of the computers is the evidence
of increase in level of parallelism and fuzziness of decisions, i.e. it is an example of
structuring under features of the natural world [8, 9]. Use of exact models and meth-
ods is restricted by need of solving problems in the conditions of uncertainty [10, 11].
One of fuzziness forms is redundancy shown in a set of versions of a solution. Such di-
versity is supported by design of digital circuits on a programmable logic which removes a
contradiction between universality and specialization of an circuit element basis: the uni-
versalization is provided with stamping of chips, and specialization – programming of
their functions [12, 13]. These and other advantages of programmable chips became a
basis for use of FPGA in case of digital component design for safety-related systems [14,
15]. Creation of versions is provided in FPGA projects with use of hardware reconfigura-
tion technologies [16, 17]. However versions of FPGA projects can also be created only
by change of a program code in case of full save of the project hardware [18]. We offer a
method which uses version redundancy of FPGA projects with the LUT-oriented architec-
ture [18] for a choice of the most effective versions of a code of programming in digital
components of safety-related systems. The choice is executed by criterion of the best at-
tributes of a checkability of the circuit and trustworthiness of the results calculated on this
circuit. The method analyzes faults of shorts between adjacent address inputs of LUT.
Faults of shorts concerns to the most typical for CMOS of integrated circuits [19].
Basic ideas of a method are described in section 2. The possibility of elimination of
a traditional contradiction between a checkability of the circuit and trustworthiness of
the results calculated by this circuit is considered. Influence of versions on faults of
shorts between adjacent address inputs of LUT is analyzed. An opportunity and feasi-
bility of the maximum distinguishing of attributes of a circuit checkability and trust-
worthiness of the results is shown. Program implementation of a method is provided
in section 3. Basic data and steps of the program execution including simulation of
operation of the circuit are defined. The results of simulation allowing to select the
version of the circuit programming are shown in the form of the table.
2 Basic Ideas of a Method
The main position of the offered method is the possibility of elimination of a tradi-
tional contradiction between a checkability of the circuit and trustworthiness of the
results calculated by this circuit. In other words, the method is based on a possibility
of development of the methods with multiple effect [20]. These methods are aimed at
simultaneous improving of attributes which are traditionally opposed each other.
What such tradition is based on? Why a norm is the method of the “Robbing Peter to
pay Paul” where one attributes improve due to deterioration in others? Whether the
multiple effect, i.e. improving of several attributes without loss in others is possible?
Responses to these questions should be looked for in consciousness of the human.
His limited models restrict our opportunities. The human thinks by exact data, i.e. inte-
gers by the nature. These are numbered data. In the consciousness the human creates a
set of any objects and numbers its elements with abstracting from the features distin-
guishing real objects. It promotes perception of the natural world at the level of replica-
tion where the method of the “Robbing Peter to pay Paul” dominates. The modern com-
puter world, generally is at this bottom level of development – replication. Array struc-
tures in computer systems and their hardware components are stamped using identical
operational elements. Software modules are also stamped for the purpose of their con-
nection to different applications [21, 22]. Additionally stamped elements allow to in-
crease throughput instead of deterioration in an index of complexity.
At the same time, the natural world doesn't create anything identical, and even
stamping generates versions, i.e. higher level of diversification in resources develop-
ment is implemented. In particular, the increase in trustworthiness based on the dou-
ble account or use of majority systems is reached not due to stamping of the duplicat-
ing elements, and thanks to their not identity, i.e. version redundancy. Systems of
critical application are development of computer systems with diversification of an
operating mode by its division on normal and emergency.
Substitution in our consciousness of actual level of diversification on the level of
replication distorts perception of methods of resources development: methods with
the multiple effect are perceived one-sidedly as methods of the “Robbing Peter to pay
Paul”, tabooing overcoming traditional contradictions between attributes of the prob-
lem solution. Being in the real natural world, the human can't but develop methods of
the multiple effect, but does it unconsciously and uses their results partially or blindly,
without guessing this use. The way to use of methods with the multiple effect lies
through diversification, i.e. distinguishing of versions.
Diversification of an operating mode of safety-related systems by its division into
normal and emergency allows to diversify requirements to a checkability of the circuit
and trustworthiness of results in relation to the normal and emergency mode. The
checkability of the circuit shall be maximum and minimum respectively in normal and
emergency modes. In a normal mode it provides the best conditions for fault detection
with methods of on-line testing, and in emergency mode it restricts action of faults.
Trustworthiness of results shall be minimum and maximum respectively in normal and
emergency modes. Low trustworthiness of results in a normal mode accompanies on-
line testing in detection of faults which are found by identification of non-authentic
results. High trustworthiness of results is an important condition of successful actions in
an emergency mode of safety-related system. Thus, opposition of a checkability of the
circuit and trustworthiness of results changes at the level of diversification on their co-
herence in the direction of support in the functional safety of safety-related systems.
The following position of a method is aimed at the maximum distinction of attrib-
utes of a checkability of the circuit and trustworthiness of results in order to direct of
them to opposite extremal values. This position is based on use of versions in a pro-
gram code for the LUT-oriented architecture of FPGA projects and versions in mani-
festation of faults like shorts. Creation of versions in a program code for the LUT-
oriented architecture of FPGA projects was considered in [19] for each pair of LUT 1
and LUT 2 if the output of LUT 1 is connected to an address input of LUT 2. The
signal from an output of LUT 1 can be transmitted to an address input of LUT 2 by
direct or inverse value based on two versions in programming of pair of LUT 1 and
LUT 2. The second version differs from the first one in inverting of all bits of
memory of LUT 1 for inverting of its output and in replacement of bits in memory of
LUT 2 for compensating of inverse on its address input. Each pair of LUT 1 and LUT
2 generates 2 versions irrespective of other such pairs. Versions of manifestation of
faults like shorts of two adjacent address inputs of LUT are shown in Fig. 1.
LUT 1 LUT 2
BA BA D C
11 10 01 00 X D 11 10 01 00 0 0
11 1 1 0 0 11 0 0 0 1 Z 0 1
D 10 1 1 0 0 C D 10 0 0 0 1 P R
1 0
C 01 0 0 0 0 C 01 0 0 0 1 1 1
00 0 0 0 0 00 1 1 1 0
Y a)
LUT 1 LUT 2
BA BA ¬D C
11 10 01 00 ¬X D 11 10 01 00 1 0
11 0 0 1 1 11 0 0 0 1 Z 1 1
R P
D 10 0 0 1 1 C D 10 1 1 1 0 0 0
C 01 1 1 1 1 C 01 0 0 0 1 0 1
00 1 1 1 1 00 0 0 0 1
Y
b)
Fig. 1. Areas E of fault manifestation in two versions of LUT units programming:
a – area P for a direct value of X; b – area P for an inverse value of X
In the left of Fig. 1, two versions in programming of pair of LUT 1 and LUT 2 in
the conditions of shorts of address inputs D and C of LUT 2 are shown.
In the first version, the LUT 1 and LUT 2 generate functions X = D B and
Z = (A B) (C D), respectively. These functions are represented in tables which
rows and columns are determined by values of 2-b codes DC and BA, respectively. The
direct value of X is calculated at an output of LUT 1 and arrives at a direct address input
D of the LUT 2. The signal Y arrives at an input C of the LUT 2 which forms signal Z at
an output. The second version calculates the same result Z at the output of LUT 2 by
using of functions ¬X and Z* = (A B) (C ¬D), where ¬D = ¬X. Inverse value of X
is calculated at an output of LUT 1 and arrives at an inverse address input D of the LUT
2. Inverse of an address input of D is provided with replacement of bits in memory of
LUT 2: two top rows of memory bits are interchanged with two bottom rows.
Fault like shorts of adjacent address inputs generates an error in the area designated
as P of different values of signals at these inputs and doesn't show an error otherwise,
i.e. in the area R where these values match. In the right parts of Fig. 1, a and Fig. 1, b,
two versions of the P and R areas are shown. In case of change of the version in pro-
gramming of LUT pair, the P and R areas are interchanged the position. It is important
as in these areas opposite results in relation to support of a checkability of the circuit
and trustworthiness will be achieved. In the P area, a checkability of the circuit raises,
and trustworthiness of results will be reduced. In the area R, on the contrary, the check-
ability of the circuit decreases, and trustworthiness of results will be increased. Thus, an
opportunity to interchange the position for sets of the P and R areas allows to inscribe
better them in sets of input data of the normal and emergency modes, i.e. to raise the
circuit checkability in a normal mode and trustworthiness of results in emergency one.
3 Program Implementation of the Offered Method
The offered method generates a set of versions in programming of LUT and provides
a choice of the version which improves a digital component of safety-related system
on two attributes: checkability of the circuit and trustworthiness of results.
Program implementation of this method defines all versions of a code of program-
ming for the given hardware implementation of the LUT-oriented architecture of the
FPGA project and all faults like shorts on which versions exert impact.
Further in the course of simulation of the circuit operation, the following actions
are performed. For each version, the summary amount of the erroneous results re-
ceived owing to action of each fault is defined. Simulation is executed for each input
word. Different areas of the normal and emergency modes are researched: the amount
of erratic results is calculated. Versions which as much as possible show errors in the
used areas of a normal mode and exclude errors in emergency one are selected.
The demonstration option of program implementation of a method is developed us-
ing Delphi 10 Seattle demo-version [23]. Program implementation of the method is
shown on the example of function evaluation in the LUT-oriented architecture support-
ed by the CAD Altera Quartus II. Basic data for the program are the description of the
circuit (amount H of inputs of the circuit, amount G of LUT and the table of connec-
tions). Inputs of the circuit and outputs of the LUT are enumerated by values 1, …, H
and H + 1, …, H + G, respectively. Address inputs A, B, C, D of each LUT are connect-
ed to inputs 1, …, H of the circuit or to outputs of prior LUT units. Their numbers are
written in the table of connections on intersection of number LUT and designation of its
address input. In the considered example H = 6, G = 4, address inputs A, B, C, D of the
LUT units 7, 8, 9 and 10 are connected to numbers 1, 2, 3, 4; 2, 3, 4, 5; 1, 2, 4, 5 and 7,
8, 9, 0, respectively. Value 0 means absence of connection. The input 6 in this part of
the circuit isn't used. The panel of step by step execution of the method is shown in Fig.
2 after execution of all steps. After start of the program, its main panel shows the table
of the circuit connections and the table "LUT Codes" in a hexadecimal number system.
Fig. 2. Program implementation of the offered method
On a step 1 the table "Versions" in which all possible versions in programming of
the circuit on FRGA are described is built. For each version 1, …, 8, the LUT, invert-
ing the output are marked by units. Besides, the table "LUT Codes Versions" in which
for LUT 2 of pairs are specified the mask codes allowing to replace value of memory
bits according to need of compensating the inverse values at address inputs is built.
On a step 2 the table "Faults" showing the list of faults depended on versions of pro-
gramming is built. The rows of this table contain two elements: number of LUT and
type of faults: A-B, B-C or C-D, i.e. shorts between address inputs of A and B, B and
C or C and D, respectively. On following step “Start”, simulation of the circuit opera-
tion at all input values of an operating mode for all versions of programming and all
set of faults is executed. After simulation the threshold separating the normal and
emergency mode is set and the table "Results" which shows quantity N and E of er-
rors appearing respectively in normal and emergency operation and also their amount
N + E and a difference N – E is created. Results of simulation show that version 1
contains identical quantity of errors (14) in both modes. Version 2 provides the best
value of checkability (19 errors) in a normal mode. Version 6 provides the best trust-
worthiness (0 errors) in emergency mode with an average value of checkability (12
errors).Version 6 is preferable in case of use in normal and emergency mode of the
same version of the circuit programming. Functioning of the circuit can be ensured with
use of different versions in normal and emergency mode [24]. In this case it is expedient
to apply versions 2 and 6 in normal and emergency mode, respectively.
4 Conclusions
The method for improving of a checkability of the circuit and trustworthiness of
results in digital components of safety-related systems is offered. The digital
components developed on FPGA with the LUT-oriented architecture are considered.
The method allows to detect better faults of digital circuits in a normal mode and to
reduce activity of faults in emergency mode of system operation. Thus, the method
increases the functional safety of safety-related systems and the objects of the
increased risk controlled by them. At the same time, not only the method, but also
questions of its development are important. How this method was received? What
objective conditions shall develop for development of this method?
The method improves two attributes which are traditionally opposed each other.
The high checkability of the circuit allows to detect timely permanent faults, but
promotes hyperactivity of the transient faults reducing trustworthiness of results.
Overcoming negative effect of such opposition of attributes became possible in safety-
related systems as a result of diversification of an operating mode by its division on
normal and emergency. It led to diversification of the input data and requirements
imposed to a checkability of the circuit and trustworthiness of results. Opposition of two
attributes became the useful to support of the functional safety of safety-related systems.
However, this opposition shall be opposite for the normal and emergency modes
where checkability and trustworthiness shall dominate respectively. Faults diversify input
data by their division into two sets defining the correct and erroneous result. However
this diversification doesn't correlate with diversification of input data for the normal and
emergency modes. Coordination of these diversifications became possible with
development of integrated circuits with a programmable logic. Version redundancy of
the program code in FPGA projects has completed the formation of objective conditions
for development of the offered method providing a choice of versions for domination of
a checkability in a normal mode, and trustworthiness – in emergency mode.
Thus, development of offered method became possible as a result of development
of resources – models, methods and means – at the level of diversification.
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