Proceedings of International Conference on Advances in Engineering and Technology
ISBN : 978 - 1505606395
Efficient Majority Logic Fault Detection With Difference-Set Codes for Memory Applications N.Muralikrishna yadav1, PG Student, Department of ECE, ASCET, Gudur, Andhra Pradesh, India. Email: muralikrishnayadav.nethi@gmail.com K. Dhanunjaya2, Head of the Department, Department of ECE, ASCET, Gudur, Andhra Pradesh, India. Email: hod.ece@audisankara.com ď€ Abstract:
Electronic space provided by silicon chips (semiconductor memory chips) or magnetic/optical media as temporary or permanent storage for data and/or instructions to control a computer or execute one or more programs. Two main types of computer memory are: (1) Read only memory (ROM), smaller part of a computer's silicon (solid state) memory that is fixed in size and permanently stores manufacturer's instructions to run the computer when it is switched on. (2) Random access memory (RAM), larger part of a computer's memory comprising of hard disk, CD, DVD, floppies etc., (together called secondary storage) and employed in running programs and in archiving of data. Memory chips provide access to stored data or instructions that is hundreds of times faster than that provided by secondary storage. Index Terms: Error correction codes, Euclidean geometry low-density parity check (EG-LDPC) codes, majority logic decoding, memory
being decoded contains errors. If there are no errors, then decoding can be stopped without completing the remaining iterations, therefore greatly reducing the decoding time. For a code with block length N, majority logic decoding (when implemented serially) requires N iterations, so that as the code size grows, so does the decoding time. In the proposed approach, only the first three iterations are used to detect errors, thereby achieving a large speed increase when N is large. It was shown that for DS-LDPC codes, all error combinations of up to five errors can be detected in the first three iterations. Also, errors affecting more than five bits were detected with a probability very close to one. The probability of undetected errors was also found to decrease as the code block length increased. For a billion error patterns only a few errors (or sometimes none) were undetected. This may be sufficient for some applications. TABLE I ONE STEP MLD EG-LDPC CODES
I. INTRODUCTION Error correction codes are commonly used to protect memories from so-called soft errors, which change the logical value of memory cells without damaging the circuit. As technology scales, memory devices become larger and more powerful error correction codes are needed. To this end, the use of more advanced codes has been recently proposed. These codes can correct a larger number of errors, but generally require complex decoders. To avoid a high decoding complexity, the use of one step majority logic decodable codes was first proposed in for memory applications. Further work on this topic was then presented in. One step majority logic decoding can be implemented serially with very simple circuitry, but requires long decoding times. In a memory, this would increase the access time which is an important system parameter. Only a few classes of codes can be decoded using one step majority logic decoding. Among those is some Euclidean geometry low density parity check (EG-LDPC) codes which were used in, and difference set low density parity check (DSLDPC) codes. A method was recently proposed to accelerate a serial implementation of majority logic decoding of DS-LDPC codes. The idea behind the method is to use the first iterations of majority logic decoding to detect if the word
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Another advantage of the proposed method is that it requires very little additional circuitry as the decoding circuitry is also used for error detection. For example, it was shown that the additional area required to implement the scheme was only around 1% for large word sizes. The proposed method that relies on the properties of DS-LDPC codes and therefore it is not directly applicable to other code classes. In the following, a similar approach for EG-LDPC codes is presented. The rest of this brief is divided into the following sections. Section II provides Existing System. Section III presents the Proposed System (Enhanced MLDD). Section IV Presents the Results and Analysis and Finally Section V gives the conclusion and Future work of this paper. II. EXISTING SYSTEM This section deals with the existing decoding methodologies used for error detection. In error detection and correction, majority logic decoding is a method to
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Proceedings of International Conference on Advances in Engineering and Technology
decode repetition codes, based on the assumption that the largest number of occurrences of a symbol was the transmitted symbol. Majority logic decoder is based on a number of parity check equations which are orthogonal to each other. So the majority result of these parity check equations decide the correctness of the current bit under decoding.
ISBN : 978 - 1505606395
general, the decoding algorithm is still the same as the majority logic decoder. The difference is that instead of decoding all codeword bits, the MLDD method stops intermediately in the third cycle, which can able to detect up to five bit flips in three decoding cycles. So the number of decoding cycles can be reduced to get improved performance. The schematic of majority logic decoder/detector is illustrated in Fig.2.
A. One Step Majority Logic Decoder As described in earlier, Majority-logic decoder is a simple and effective decoder capable of correcting multiple bit flips depending on the number of parity checksum equations. It consists of four parts: 1) a cyclic shift register; 2) an XOR matrix; 3) a majority gate; 4) an EXOR gate for error correction, as illustrated in Fig.1.
Fig.2. Schematic of Majority Logic Decoder/Detector (MLDD)
Fig.1. One step Majority Logic Decoder for (15, 7) EGLDPC Codes In one step majority logic decoding, initially the code word is loaded into the cyclic shift register. Then the check equations are computed. The resulting sums are then forwarded to the majority gate for evaluating its correctness. If the number of 1’s received in is greater than the number of 0’s which means that the current bit under decoding is wrong, and a signal to correct it would be triggered. Otherwise the bit under decoding is correct and no extra operations would be needed on it. In next, the content of the registers are rotated and the above procedure is repeated until codeword bits have been processed. Finally, the parity check sums should be zero if the codeword has been correctly decoded. In this process, each bit may be corrected only once. As a result, the decoding circuitry is simple, but it requires a long decoding time if the code word is large. Thus, by one-step majority-logic decoding, the code is capable of correcting any error pattern with two or fewer errors. For example, for a code word of 15-bits, the decoding would take 15 cycles, which would be excessive for most applications.
Initially the code word is stored into the cyclic shift register and it shifted through all the taps. The intermediate values in each tap are given to the XOR matrix to perform the checksum equations. The resulting sums are then forwarded to the majority gate for evaluating its correctness. If the number of 1’s received is greater than the number of 0’s which would mean that the current bit under decoding is wrong, so it move on the decoding process. Otherwise, the bit under decoding would be correct and no extra operations would be needed on it. Decoding process involving the operation of the content of the registers is rotated and the above procedure is repeated and it stops intermediately in the third cycle. If in the first three cycles of the decoding process, the evaluation of the XOR matrix for all is “0,” the code word is determined to be error-free and forwarded directly to the output. If the error contains in any of the three cycles at least a “1,” it would continue the whole decoding process in order to eliminate the errors. Finally, the parity check sums should be zero if the code word has been correctly decoded. In conclusion the MLDD method is used to detect the five bit errors and correct four bit errors effectively. If the code word contain more than five bit error, it produces the output but it did not show the errors presented in the input. This type of error is called the silent data error. Drawback of this method is did not detecting the silent data error and it consuming the area of the majority gate. The schematic for this memory system is shown in Fig.3. It is very similar to the one shown in fig.1; additionally the control unit was added in the MLDD module to manage the decoding process (to detect the error).
B. Majority Logic Decoder/Detector (MLDD) In order to overcome the drawback of MLD method, majority logic decoder/detector was proposed, in which the majority logic decoder itself act as a fault detector. In
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Proceedings of International Conference on Advances in Engineering and Technology
Fig.3. Schematic of memory system with MLDD Overall operation of the MLDD is illustrated in Fig.4.
ISBN : 978 - 1505606395
The data words are initially encoded and then the codeword is stored in the memory. When the memory is read, the codeword is then fed through the enhanced MLDD before sent to the output for further processing. The code word contains message bits and parity or redundant bits. The code efficiency is defined as the ratio of message bits to the number of transmitted bits per block. The silent data error detection using enhanced MLDD algorithm performs the decoding as in the MLDD with some modifications. When the MLDD having more than 5 errors will be detected and corrected by the enhanced MLDD method. The MLDD is used the control unit for detecting the error. If it has any error in this iteration it will be perform with the modified algorithm is illustrated in Fig.6. It is used to avoid silent data corruption of the MLDD output. This would increase the error detection capabilities at the expense of the errorcorrection capabilities. In this algorithm up to four errors will be done as in the MLDD algorithm. If it has more than four errors will detected by after third iteration. Then correction will be done by after nth iteration.
Fig.4. MLDD Algorithm III PROPOSED SYSTEM (ENHANCED MLDD) This section presents an enhanced version of the ML decoder/detector that improves the designs presented before, by detecting the silent data error. Memory schematic of an enhanced MLDD is illustrated in Fig.5.
Fig.6. Enhanced MLDD algorithm A. Sorting network
Fig.5. Memory schematic of an Enhanced MLDD
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A sorting network is an abstract mathematical model of a network of wires and comparator modules that is used to sort a sequence of numbers. Each comparator connects two wires and sorts the values by outputting the smaller value to one wire, and the larger to the other. The main difference between sorting networks and comparison sorting algorithms is that with a sorting network the sequence of comparisons is set in advance, regardless of the outcome of previous comparisons. This independence of comparison sequences is useful for parallel execution of the algorithms.
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Proceedings of International Conference on Advances in Engineering and Technology
Fig.7 (a): Comparator circuit A sorting network consists of wires and comparators that will correctly sort all possible inputs into ascending order. . So it used to reducing the gates and their interconnections of the majority gate. Each wire carries with it a value, and each comparator takes two wires as input and output. When two values enter a comparator, the comparator emits the lower value from the top wire, and the higher value from the bottom wire. Using sorting network number of gates reduced in the majority gate. Initially it compares the inputs using comparator circuit. Comparator consist of AND gate and then OR gate for selecting maximum and minimum value shown in Fig.7 (a). OR gate producing maximum value will be placed in top of the wire and the AND gate producing minimum value will be placed in bottom of the wire in the comparator circuit.
Fig.7 (b): 2-bit sorter
ISBN : 978 - 1505606395
Fig.8.Behavioral simulation waveform for the fault secure encoder
Fig.9.Post route simulation waveform for the fault secure encoder The behavioral simulation and post route simulation waveforms for the fault secure memory system is shown in Fig.10 and Fig.11. In Fig.10 inputs are I (information vector), clk, wen(write enable), ren(read enable), and e (error vector) to introduce an error. In this the encoded word is given to the memory for this if ‘wen’ is ‘1’(high) data is write into memory in a perticular address, here address line is the information vector. If ‘ren’ is high data is read and given as an output of memory. The memory output is combination of coded vector and error vector. This memory output is given as an input to the corrector which corrects the coded word. This corrected coded word is given to the detector to check whether coded word is correct or not.At the corrector side detector sinal is ‘md’.
Each of the vertical lines represents one comparator which compares two bits and assigns the larger one to the top output and the smaller one to the bottom. Those value given to the AND gate for getting the minimum value and given to the OR gate for selecting the maximum value shown in Fig.7 (b). IV.RESULTS AND ANALYSIS 4.1 Simulation Results: The behavioral simulation and post rout simulations waveforms for the fault secure encoder is shown in Fig.8 and Fig.9. In the Fig.8,the input is information vector and output is the detector output d which detects the errors in the encoder. First information vector is given to encoder it gives encoded vector as an output which is n-bit length. This encoded vector is given as input to the detector. Any error is present in encoded vector the detector output is ‘1’. If it is ‘0’ encoded codeword is correct.
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Fig.10.Behavioral simulation waveform for the fault secure memory system
75 International Association of Engineering and Technology for Skill Development
Proceedings of International Conference on Advances in Engineering and Technology
ISBN : 978 - 1505606395
After the HDL synthesis phase of the synthesis process, use the RTL Viewer to view a schematic representation of the pre-optimized design in terms of generic symbols that are independent of the targeted Xilinx device, for example, in terms of adders, multipliers, counters, AND gates, and OR gates. The RTL schematic for the Fault secure encoder generated by the Xilinx Synthesis tool is shown in Fig.12 below.
Fig.11.Post route simulation waveform for the fault secure memory system
Fig.12.RTL Schematic for Fault secure encoder Table II Design Implementation summary for fault secure memory system
The RTL schematic for the memory generated by the Xilinx Synthesis tool is shown in Fig.13 below.
Fig.13.RTL Schematic for memory The RTL schematic for the Fault secure memory system generated by the Xilinx Synthesis tool is shown in Fig.14 below.
Timing summary Minimum period: 3.516ns (Maximum Frequency: 284.414MHz) Minimum input arrival time before clock: 4.711ns Maximum output required time after clock: 55.255ns Maximum combinational path delay: 55.733ns 4.2 RTL Schematic
Fig.14.RTL Schematic for Fault secure memory system 4.3 Technology schematic: The technology schematic for the Fault secure memory system generated by the Xilinx Synthesis tool is shown in Fig.15 below.
In integrated circuit design, register transfer level (RTL) description is a way of describing the operation of a synchronous digital circuit. In RTL design, a circuit's behavior is defined in terms of the flow of signals (or transfer of data) between hardware registers, and the logical operations performed on those signals.
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Proceedings of International Conference on Advances in Engineering and Technology
ISBN : 978 - 1505606395
(corrector), and detector circuitries). The main advantage of the proposed architecture is using this detect-and-repeat technique we can correct potential transient errors in the encoder or corrector output and provide fault-tolerant memory system with fault-tolerant supporting circuitry. And also takes less area compared to other ecc techniques and in this architecture there is no need of decoder because we use systematic generated matrix. 5.2. Future work:
4.4 Floor plan of an fault secure encoder and decoder for memory:
Fault secure encoder and decoder for memory applications is to protect the memory and supporting logic from soft errors. The proposed architecture tolerates transient faults both in the storage unit and in the supporting logic. Scope for further work is instead of memory we use nano memory which provides smaller, faster, and lower energy devices which allow more powerful and compact circuitry.
The floor plan for the Fault secure memory system generated by the Xilinx Synthesis tool is shown in Fig.16 below.
VI. REFERENCES
Fig.15.Technology schematic for fault secure encoder and decoder for memory
[1] Pedro Reviriego, Juan A. Maestro, and Mark F. Flanagan, “Error Detection in Majority Logic Decoding of Euclidean Geometry Low Density Parity Check (EG-LDPC) Codes”, IEEE Transactions on Very Large Scale Integration (VLSI) Systems, Vol. 21, No. 1, January 2013. [2] R. C. Baumann, “Radiation-induced soft errors in advanced semiconductor technologies,” IEEE Trans. Device Mater. Reliab, vol. 5, no. 3, pp. 301–316, Sep. 2005. [3] M. A. Bajura, Y. Boulghassoul, R. Naseer, S. DasGupta, A. F.Witulski, J. Sondeen, S. D. Stansberry, J. Draper, L. W. Massengill, and J. N. Damoulakis, “Models and algorithmic limits for an ECC-based approach to hardening sub-100-nm SRAMs,” IEEE Trans. Nucl. Sci., vol. 54, no. 4, pp. 935–945, Aug. 2007. [4] R. Naseer and J. Draper, “DEC ECC design to improve memory reliability in sub-100 nm technologies,” Proc. IEEE ICECS, pp. 586–589, 2008. [5] S. Ghosh and P. D. Lincoln, “Dynamic low-density parity check codes for fault-tolerant nano-scale memory,” presented at the Foundations Nanosci. (FNANO), Snowbird, Utah, 2007.
V.CONCLUSION AND FUTURE SCOPE 5.1. Conclusion: In this project FPGA implementations of fault secure encoder and decoder for memory applications. Using this architecture tolerates transient faults both in the storage unit and in the supporting logic (i.e., encoder, decoder
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[6] S. Ghosh and P. D. Lincoln, “Low-density parity check codes for error correction in nano-scale memory,” SRI Computer Science Lab., Menlo Park, CA, Tech. Rep. CSL0703, 2007. [7] H. Naeimi and A. DeHon, “Fault secure encoder and decoder for memory applications,” in Proc. IEEE Int. Symp. Defect Fault Toler. VLSI Syst., 2007, pp. 409–417.
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Proceedings of International Conference on Advances in Engineering and Technology
ISBN : 978 - 1505606395
[8] B. Vasic and S. K. Chilappagari, “An information theoretical framework for analysis and design of nano-scale fault-tolerant memories based on low-density parity-check codes,” IEEE Trans. Circuits Syst. I, Reg. Papers, vol. 54, no. 11, pp. 2438–2446, Nov. 2007. [9] H. Naeimi and A. DeHon, “Fault secure encoder and decoder for Nano-memory applications,” IEEE Trans. Very Large Scale Integr. (VLSI) Syst., vol. 17, no. 4, pp. 473– 486, Apr. 2009. [10] S. Lin and D. J. Costello, Error Control Coding, 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, 2004. [11] S. Liu, P. Reviriego, and J. Maestro, “Efficient majority logic fault detection with difference-set codes for memory applications,” IEEE Trans. Very Large Scale Integr. (VLSI) Syst., vol. 20, no. 1, pp. 148–156, Jan. 2012. [12] H. Tang, J. Xu, S. Lin, and K. A. S. Abdel-Ghaffar, “Codes on finite geometries,” IEEE Trans. Inf. Theory, vol. 51, no. 2, pp. 572–596, Feb. 2005.
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