US 20040243887 A1 Abstract A method and an apparatus verifies the correctness of the error correcting code algorithm and the correctness of the error correcting code implementation. An error injection module is used to inject random errors into an ECC circuit between an encoder and a decoder. The encoder encodes data bits with check bits to produce an encoded signal. A decoder decodes the encoded signal, after modification by the error injection module. The output of the decoder may be a zero error signal, a signal error signal, a multiple error signal, and an error location signal. The output signal is compared to expected values to determine if an error exists in the ECC or the ECC circuit.
Claims(7) 1-11. (cancelled). 12. A method for verifying an error correcting code (ECC) operating on an ECC circuit, comprising:
providing a data input signal to a data encoder; generating an ECC encoded data signal comprising data bits and check bits; on a random basis, injecting one of a single error signal and a multiple error signal into the ECC encoded data signal, and passing the ECC encoded data signal to indicate a no error condition, thereby producing; and an output signal; and decoding the output signal to produce one or more decoded output signals indicative of one of the no error condition, a single error condition and a multiple error condition. 13-15. (cancelled). 16. The method of comparing the one or more decoded output signals with corresponding expected signals; and if the one or more decoded output signals and the corresponding expected signals do not match, declaring an error in the ECC or the ECC circuit. 17. The method of 18. The method of 19. The method of Description [0001] The technical field is error correcting code for storage or communications systems. [0002] Communication and storage systems are subject to errors that may affect operation of connected systems. A typical error may result when a particular memory location is exposed to one or more a particles. Such radiation may cause a data bit stored in the memory location to flip from a “1” to a “0.” [0003] Error correcting codes (ECC) are used to enhance reliability and state integrity of communications and storage systems. Error correcting codes are known that will correct a single error, and will detect, but not correct, a double error. Other ECCs will detect and correct multiple errors. For ECC applications, memory array chips may be organized so that errors generated in a chip can be corrected by the ECC. [0004] Correction of single bit errors and detection of double bit errors may be accomplished by use of check bits. A typical ECC implementation appends a number of check bits to each data word. The appended check bits are used by ECC logic circuits to detect errors within the data word. The simplest and most common form of error control is implemented through the use of parity bits. A single parity bit is appended to a data word and assigned to be a 0 or a 1, so as to make the number of 1's in the data word even in the case of even parity codes, or odd in the case of odd parity codes. [0005] Prior to transmission of the data word in a computer system, the value of the parity bit is computed at the source point of the data word and is appended to the data word. On receipt of the transmitted data word, logic at the destination point recalculates the parity bit and compares it to the received, previously appended parity bit. If the recalculated and received parity bits are not equal, a bit error has been detected. Use of parity codes has the disadvantage, however, of not being able to correct bit errors and not being able to detect even numbers of bit errors. For example, if a data bit changes from a 0 to a 1 and another data bit changes from a 1 to a 0 (a double bit error), the parity of the data word will not change and the error will be undetected. [0006] By appending additional parity bits to the data word, each corresponding to a subset of data bits within the data word, the parity bit concept may be extended to provide detection of multiple bit errors, or to determine the location of single or multiple bit errors. Once a data bit error has been detected, logic circuits may be used to correct the erroneous bit, providing single error correction. [0007] A well known error correction code is the Hamming code, which may be a SEC-DED code, for example. The ECC appends a series of check bits to the data word as it is stored in memory. Upon a read operation, the retrieved check bits are compared to recalculated check bits to detect and to locate (i.e., correct) a single bit error. By adding more check bits and appropriately overlapping the subsets of data bits represented by the check bits, other error correcting codes may provide for multiple error correction and detection. [0008] Verifying the correctness of the error correcting code includes two steps: verifying the underlying algorithm of the error correcting code and verifying the implementation of the error correcting code on a hardware device or on a simulation of the hardware device. Current methods for verifying the error correcting code do not link these two steps, and hence do not provide a complete verification. An example of this problem may be shown with respect to linear codes. Linear codes are constructed using properties based on Galios field arithmetic. The proof of the properties in concept may be made within the mathematical framework of Galois fields. Based on this concept, a generator matrix (known as a G matrix), a parity matrix (known as an H matrix), and different syndrome vectors corresponding to various error scenarios are generated, either by hand or by a computer program. A single-error correcting, double-error detecting (SEC-DED) code would have an H matrix in which no two columns are identical and in which the Galois field addition of any two columns is not equal to any column in the H matrix. The mathematical proof of the concept does not detect any error introduced during the generation of the G and H matrices and the syndrome vectors. The G and H matrices and the syndrome vectors are then used in a high-level language to generate the error correcting code circuitry, which may be implemented as a hardware device or a simulation of the hardware device. Verification of the implementation is completed by checking whether the implementation provides expected outputs based on the G and H matrices and the syndrome vectors. [0009] One problem with this conventional approach comes from errors that may occur during generation of the G and H matrices and the syndrome vectors. Such errors may go undetected because no automated tool exists to directly produce the error correcting code circuitry from the mathematical properties. [0010] A method and an apparatus verifies the correctness of the error correcting code algorithm and the correctness of the error correcting code implementation. An error injection module is used to inject random errors into an ECC circuit between an encoder and a decoder. The encoder encodes data bits with check bits to produce an encoded signal. A decoder decodes the encoded signal, after modification by the error injection module. The error injection module may inject zero errors. Alternatively, the error injection circuit may inject a single error or multiple errors. The output of the decoder may be a zero error signal, a single error signal, a multiple error signal, and an error location signal. Other signals are also possible. The output of the decoder is compared to expected values for each signal using a monitoring module. Any differences between the output signals and the expected values may indicate an error in the ECC or in the circuit used to implement the ECC. [0011] The ECC may be verified by implementing the verification apparatus in an actual hardware device. In this embodiment, the error injection module and the monitoring module may be located on a same chip as the decoder and the encoder. Alternatively, the error injection module and the monitoring module may be located on chips separate from the decoder and the encoder. The ECC verification apparatus may also be implemented as a simulation of the actual hardware device or in a formal verification model of the actual hardware. [0012] The detailed description will reference the following figures, in which like numerals refer to like items, and in which: [0013]FIGS. 1A and 1B are a block diagrams of an error correcting circuit; [0014]FIG. 2 is a block diagram of an apparatus for verifying an error correcting code and circuit; and [0015]FIGS. 3A and 3B are flow charts showing processes executed on the apparatus of FIG. 2. [0016] Error correcting code (ECC) circuits are widely used in semiconductor memory designs to correct single-bit errors and to detect double-bit errors. One common ECC code is the SEC-DED (single error correction—double error detection) code. Other ECC codes are capable of detecting more than two errors and correcting more than single errors. [0017] The ECC circuits perform their error checking functions by generating a number of check bits for a specific number of data bits, and then writing the check bits to memory with the data bits. The check bits are then used during subsequent read-write cycles or other memory accesses to verify the correct values for the data bits. The number of check bits required to implement the ECC depends on the number of data bits being read. As shown in Table 1, as a number of data bits being read increases, the number of required ECC bits also increases.
[0018] Hardware to implement ECC check bits using current systems is illustrated in FIG. 1 [0019]FIG. 1B is a block diagram of a portion of the ECC block [0020] In FIG. 1B, a circuit [0021] Current approaches for generating the ECC and associated circuitry (hardware or hardware simulation) do not account for possible errors in the underlying algorithm. Thus, application of the ECC in an implementation may not ensure all errors are correctly corrected or detected. This may be particularly true when the ECC is a combination of linear codes and arithmetic codes, or some other custom codes that do not follow standard procedures. [0022] To overcome this problem, an apparatus and a method subject the implementation of the ECC circuit to the various errors the ECC circuit is expected to correct/detect. The apparatus and the method verifies the ECC concept, the algorithm, and the implementation simultaneously. [0023]FIG. 2 is a block diagram illustrating the apparatus and the method for verifying ECC. In FIG. 2, an apparatus [0024] The method and the apparatus [0025] The decoder [0026] The error injection circuit [0027] The apparatus [0028] The apparatus [0029] To verify proper operation of the ECC, including the underlying algorithm and the ECC circuit, the apparatus [0030] The apparatus [0031] In the embodiment shown in FIG. 2, the data bus coupling the transmitter [0032]FIGS. 3A and 3B illustrate processes that may be executed using the apparatus [0033] In block [0034]FIG. 3B illustrates a process [0035] The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention as defined in the following claims, and their equivalents, in which all terms are to be understood in their broadest possible sense unless otherwise indicated. Referenced by
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