Abstract:
An integrated solid state memory device includes addressable memory locations. In use, an address port receives an address identifying at least one memory location and associated verification information (e.g., parity or error correcting information) for verifying the address. Decoding logic is responsive to a received address to decode the address and verification logic is responsive to a received address and a received verification portion to verify the received address. By providing address verification within a solid state memory device, it is possible to ensure a higher security of operation of a computer system incorporating such a memory device, as errors which might develop, for example, between a memory controller and individual memory devices can be detected. As well as being useful for normal operation, such a memory device facilitates checking of the operating limits of a system as bus speeds and memory access speeds increase. The verification logic can be configured, for example, to prevent access to or modification of the memory locations and/or in the case of a read operation, to prevent output from the device of the content of an addressed memory location where address verification is negative. An error signal could also be generated where address verification is negative. The error signal could be used simply to report a fault or to cause a retry of the addressing operation. Where the memory device includes separate memory banks, the address verification could be performed at one or more levels within the device, for example down to the memory bank level.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to memory address checking in computer systems. 
     Computer systems typically include mechanisms for ensuring the correctness of data, for example through the use of parity and error correction codes. Such mechanisms are often applied to the data paths between processing elements, I/O elements and main memory. Indeed, it is common for parity or error correction codes to be stored along with data in main memory. As a result of this the parity or error correction codes are available to check the validity of data when subsequently read from memory. Accordingly, it is possible for the validity and correctness of data to be verified at all stages along the data path from the processing elements to memory and back again. 
     It is also known to employ parity or error correction codes for ensuring the correctness of addresses on an address bus. However, the protection provided by the use of such codes for checking addresses effectively stops at the entry to the memory subsystem, such that address errors within the memory subsystem can go undetected. 
     Accordingly, an aim of the present invention is to improve the degree of security of memory operation in a computer system. 
     SUMMARY OF THE INVENTION 
     Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims. 
     In accordance with one aspect of the invention, there is provided a solid state memory device including a plurality of addressable memory locations. During operation of the memory device, an address port receives an address identifying at least one memory location and associated verification information for verifying the address. Decoding logic is connected (directly or indirectly) to the address port and is operable to respond to an address received at the address port to decode the address. Verification logic is connected (directly or indirectly) to the address port and is operable to respond to an address and associated verification information received at the address port to verify the received address. 
     By providing address verification within a solid state memory device, it is possible to extend the verification of addresses into the memory devices themselves. Previously, address verification was only possible externally to solid state memory devices. In this manner, the addresses can be checked from the point of encoding to the point of decoding within a computer system. 
     By providing a memory device in accordance with the invention it is possible to ensure a higher security of operation of a computer system incorporating such a memory device, as errors which might develop or be present due to incorrect assembly between a memory controller and individual memory devices can be detected. Also, an embodiment of the invention can be used to verify overall reliability of a system. For example, it would be possible to strobe a memory chip at higher and higher clock rates until a fault is detected, for example due to capacitive or other effects inside or between the memory system devices, thus establishing reliable operating parameters for a memory system and a computer system incorporating such memory devices. 
     The verification logic can be configured in different ways. For example, it can be configured to be operable to prevent access to the memory locations where address verification is negative. Alternatively, or in addition, in the case of a read operation the verification logic is operable to prevent output from the device of the content of an addressed memory location where address verification is negative. Alternatively, or in addition, in the case of write operation the verification logic is operable to prevent modification of the content of an addressed memory location where address verification is negative. It can also be configured to be operable to inhibit the output of the decoding logic where address verification is negative. Generally, however, the verification logic is operable to prevent modification of any memory location where address verification is negative. 
     Preferably, the verification logic is operable to indicate an error where address verification is negative. More preferably, the memory device comprises an error output for returning an error signal where address verification is negative. The error signal can be used simply to report a fault. Alternatively, it can be used to cause a memory controller to retry a memory addressing operation. 
     The verification information could comprise an error detecting code such as, for example, one or more parity bits. Alternatively, or in addition, the verification information could comprise an error correcting code. In this latter case, the verification logic could be configured to correct an invalid address based on the error correcting code, where possible. 
     Preferably, the address port comprises a plurality of device contacts for connection to a bus or to control lines to a memory controller. A data port can be provided for receiving write data associated with a received address and a data register can be provided for holding write data pending verification of the received address. Where the data is also associated with data verification information, the verification logic can be operable to verify that data and to prevent writing of data to the memory where verification is negative. 
     In a preferred implementation, the memory device is an integrated memory chip. The integrated memory device can comprise a plurality of memory banks. The verification and decoding logic can be provided at one or more levels within the device, for example down to the memory bank level. 
     In accordance with another aspect of the invention, there is provided a solid state memory device comprising a plurality of addressable memory locations, a data port for receiving data for storage in at least one memory location including associated data verification information for verifying the data, and verification logic responsive to received data and data verification information to verify the received data and to prevent storage of that data where verification is negative. Thus controlled storage can be made dependent upon the validity of received data. 
     In accordance with a further aspect of the invention, there is provided a computer system. The computer system includes a processing unit, a bus connected to the processing unit and including address lines and verification information lines for an address and associated verification information, a memory controller connected to the bus and at least one solid state memory device as described above and connected to the memory controller. The bus can include an error line for an error signal or provision for a negative acknowledgement indicative of a negative address verification at the memory device. 
     In accordance with a further aspect of the invention, there is provided a method of addressing a memory location within a solid state memory device comprising: receiving an address at the memory device with associated verification information for verifying the address; and verifying the received address within the memory device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the present invention will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which: 
     FIG. 1 is a schematic overview of a computer system; 
     FIG. 2 is a schematic overview of a memory subsystem; 
     FIG. 3 is a schematic overview of an example of a memory device according to the invention; 
     FIG. 4 is a schematic view of an alternative configuration of a memory device in accordance with the invention; 
     FIG. 5 is a schematic view of a further example of a memory device in accordance with the invention; 
     FIG. 6 is a schematic view of a further example of a memory device in accordance with the invention; 
     FIG. 7 is a schematic overview of a further example of a memory device in accordance with the invention; and 
     FIG. 8 is a perspective view of a memory device in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic overview of a computer system incorporating an embodiment to the present invention. FIG. 1 illustrates a processor  12  and a memory subsystem  14 . Connecting the processing  12  and the memory subsystem  14  is a bus structure comprising an address bus  15  and a data bus  19  with, in addition, an error line  18 . The address bus  15  and the data bus  19  are used for passing addresses and data between the processor and the memory subsystem and other components (not shown) connected thereto. The error line  18  is for reporting an address error as will be explained in more detail later. It should be noted that the error line  18  is optional. It will be appreciated that the computer system would typically include further components, not shown, including, for example, a keyboard, other input devices, a display, back-up storage and communication devices. 
     FIG. 2 is a schematic overview of an example of a memory subsystem  14  of an embodiment of the invention. As shown in FIG. 2, the memory subsystem  14  includes a memory controller  20  connected to a memory subsystem bus, including an address bus  25 , a data bus  29 , timing and control lines  24  and an error line  28 . The address bus  25  is for passing addresses from the memory controller to individual memory devices  22 . The data bus  29  is for passing data between the memory controller and the memory device in both directions. The timing and control lines  24  are for passing timing information and control information from the memory controller  20  to the individual memory devices  22 . The error line  28  is an optional line for passing an error signal from a memory device  22  to the memory controller  20 . 
     FIG. 3 is a schematic overview of an example of a memory device  22  in accordance with the present invention. As shown in FIG. 3, the address bus  25  includes an address portion  26  and a verification portion  27 . The address portion  26  includes the address for addressing a memory location within a memory array  33 . The verification portion  27  contains verification information for verifying the correctness of the address. The verification information could, for example, be in the form of error correcting codes (ECC) or error detecting codes (EDC). An example of an EDC is the use of one or more parity bits. However, the verification information is not limited to these examples and could take some other form. It will be appreciated that there are typically a plurality of address lines  26  (for example 7, 8, 9, 16, 32, etc. lines), and the verification information lines  27  may also comprise a plurality of bits (for example 1, 2, 3, etc. bits). It will also be appreciated that an address may comprise more than one part supplied on the address bus  25  at separate times under the control of timing information supplied on the clock lines  24 . Clock logic  34  is responsive to the clock signals supplied on the clock lines  24  for generating internal clock signals for controlling the various elements of the memory device as represented by the dotted clock lines  24 I. 
     When an address is supplied to the memory device  22 , it is initially buffered in an address buffer, or address register  35 . Similarly, with a write operation to memory, write data from the data bus  29  is buffered in a data buffer  39  pending addressing of the memory location within the memory  33 . 
     The address and verification information is supplied from the address buffer  35  to control and verification logic  30 . The control and verification logic  30  is arranged to perform conventional verification operations on the address using parity or other EDC, ECC, or other verification information. If verification is positive and the address checks out, the address information is passed to the row (Y) decoder  31  and column (X) decoder  32 . The Y decoder  31  and X decoder  32  decode the input address in order to address a specific location (or group of locations) within the memory array  33 . 
     In the case of a write operation, the control and verification logic also causes the data buffer to supply the data to the memory array  33  via sense and gating circuitry including sense amplifiers and gating logic  38  in accordance with the correct timing for writing data to the memory array. In the case of a read operation, the addressing of the memory array, along with appropriate sensing of the memory array, causes data to be output from the addressed location or locations to the data buffer  39  via the sense and gating circuitry  38 , from which it can then be output over the data bus  29 . 
     If the verification is negative (i.e. there is an error in the address or verification information), then the address information from the lines  26  is not passed to the Y decoder  31  and the X decoder  32 . Optionally an error signal can be supplied to the error line  28  for supply to the memory controller and/or to the processor  10 . The error signal could be used simply to indicate the presence of the data error, or could be used to cause the memory controller to retry addressing of the memory device  22 . 
     In the case where the verification information is ECC information, the control and verification logic could be arranged, in a conventional manner, to attempt correction of the address information. If this is possible, then addressing of the memory location or locations within the memory array  33  by means of the Y decoder  31  and X decoder  32  can proceed. If correction of the address information is not possible, then the addressing of the memory array  33  by the Y decoder  31  and X decoder  32  is inhibited, and optionally an error signal  28  is generated. 
     It should be noted that FIG. 3 is a schematic overview of a memory device  22 , and details typically found in a memory device have not been shown in FIG.  3 . For example, the control and verification logic receives a data signal from the line  29  indicating whether the data operation is a write or a read operation. Also details of the memory array including the appropriate sense and control structures is not shown in FIG.  3 . 
     FIG. 4 is a schematic representation of an alternative example of a memory device in accordance with the present invention. Similar references are used in FIG. 4 to those used in FIG.  3 . Thus, there is an address buffer  45  for a received address, including an address portion  46  for address information from the lines  26  and a verification portion  47  for verification information from the verification line(s)  27  of the address bus  25 . Control and verification logic  40  receives both the address and verification information from the address buffer  45 . 
     In FIG.  4 . the address information from the address portion  46  of the address buffer  45  is supplied directly to a Y decoder  41  and an X decoder  42 . In the example of FIG. 4, the control and verification logic is operable to control the operation of the Y and X decoders  41  and  42  via control lines  40 C. Accordingly, the control and verification operations performed by the verification logic  40  can be performed in parallel with the Y decoding and X decoding operations in the Y decoder  41  and X decoder  42 . Where the address verification is positive, the control and verification logic  40  can enables the decoded addresses from the Y and X decoders  41  and  42  to be applied to the memory array  43  for addressing a location or locations within the memory array  43 . 
     Signals can also be supplied to the data buffer  49  to enable writing of information from the data buffer  49  to the address location or locations  43  in the case of a write instruction, or reading of data from the address location or locations in the memory array  43 , in the case of a read operation. If, however, the address verification operation is negative, that is the address does not check out and there is an error in the address or the verification information, then the output of the decoded address signals from the Y and X decoders  41  and  42  is prevented. This can be achieved by selectively disabling gates at the outputs of the Y and X decoders  41  and  42 , thereby preventing addressing of the memory location in the memory array  43 . By providing simultaneous decoding and address verification any impact on overall performance due to the verification operations can be minimised. 
     As with the example of FIG. 3, an error signal can optionally be provided on the optional error line  28 . Also, as with the example of FIG. 3, the details of the memory array  43  can be conventional enabling writing and/or reading, with control thereof being provide in response to a write/read signal supplied to the control and verification logic  40  from the data bus  29 . Thus, appropriate sense and gating circuitry  48  can be provided in a conventional manner. In FIG. 4, for reasons of clarity, the internal clock signals lines CKI have not been shown. 
     However, what is shown is a connection between the control and verification logic and the data buffer  49 . Optionally, therefore, verification of the data supplied to the data buffer can be affected by the control and verification logic. The results of verification using parity, EDC or ECC can be performed in the same manner as for the received addresses. The storage of data in the case of an error being detected in the received data can therefore be prevented, if desired, by inhibiting the output from the data buffer  49 . It should be noted that the memory device of FIG. 3 could also be modified to include verification of the received data. 
     FIG. 5 is a schematic overview of a further example of a memory device according to an embodiment of the invention. In FIG. 5, similar reference numerals are used to those in the earlier embodiments. In FIG. 5, separate Y and X address buffers  55 X and  55 Y are provided. In this case the address buffers only receive the active address portion from the lines  26  and do not receive the address verification portion from the line(s)  27 . Both the active address portion from the lines  26  and the address verification portion from the line(s)  27  are supplied to the control and verification logic  50 . A Y decoder  51  and X decoder  52  are connected to receive the address information from the Y and X address buffers  55 Y and  55 X, respectively. A data buffer  59  is used for receiving write data from the data bus  29  and for buffering read data for supply to the data bus  29 . A data in/data out signal determining whether a write or a read operation is to be performed is applied from the data bus  29  to the verification logic  50 . The control and verification logic  50  also receives one or more clock signals on lines  24  for controlling the timing of the operation of the memory device  22 . 
     The embodiment of FIG. 5 also differs from that of FIG. 4 in that in FIG. 5, the control of the access to the memory is achieved by directly controlling the sense and gating circuitry  58 . Accordingly, in an embodiment to the invention as shown in FIG. 5, the speed of operation of the memory array may be further improved in that addressing of the memory array by the Y decoder  51  and the X decoder  52  can always be enabled, control of whether data is input to or output from the memory array  53  being instead achieved by the control and verification logic  50  controlling the operation of the sense and/or gating circuitry  58 . This can reduce delays in operation of the memory device. 
     Typically, today, a memory device does not comprise a single block of memory in a single memory array such as memory array  53  of FIG.  5 . Typically, the memory array is divided into a number of memory banks with each bank being represented by a memory array. Such a structure is represented schematically in FIG.  6 . The provision of an array of this type is to improve the speed of access to the individual locations within the memory array by avoiding excessively long lines within the memory array which would lead to unacceptable signal delays due to capacative and other effects. Similar reference signs are used in FIG. 6 to those used in the earlier figures. However, a more detailed schematic overview of the array is shown. 
     In FIG. 6,  66 X and  66 Y represent separate X and Y address buffers for receiving the address portion  26  (e.g. A 0 -A 7  from the address bus  25 ). The content of the X address buffer  66 X is supplied to X decoders  62 . 0  and  62 . 1 . The output of the Y address buffer  66 Y is supplied to Y address decoders  61 . 0  and  61 . 1 . The address portion  26  (e.g. A 0 -A 7 ) and the verification portion  27  (e.g. A 8 ) from the address bus  25  are supplied to the control and verification logic  60 . Outputs from the control and verification logic  60  are supplied to the sense and gating circuitry  68 . 00 ,  68 . 01 ,  68 . 10  and  68 . 11  for selectively enabling access to the memory banks  63 . 00 ,  63 . 01 ,  63 . 10  and  63 . 11 , respectively. A data buffer  69  connected to the data bus  29  is also connected to the sense and gating circuitry  68 . 00 ,  68 . 01 ,  68 . 10  and  68 . 11  for the input and output of data signals. An optional error line  28  is also provided from the output of the control and verification logic  60  for optionally indicating an error when the address verification is negative. In overall operation, the example of FIG. 6 is substantially the same as that of FIG. 5 with selective gating of the sense and gating circuitry  68 . 00 ,  68 . 01 .  68 . 10  and  68 . 11  to enable writing to an address memory location or locations or reading from an address memory location or locations where address verification is positive, and preventing writing to or reading from an address memory location where address verification is negative. As in FIG. 5, internal clock signal and other control lines are not shown for reasons of clarity. 
     FIG. 7 is a schematic overview of an alternative embodiment of the memory device of FIG. 6 where the address verification is provided at the memory bank level, rather than at the level of the device as a whole. It will be noted that similar reference signs are used in FIG. 7 to those used in FIG.  6 . Thus,  75 X represents an X address buffer and  75 Y represents a Y address buffer. In FIG. 7, it will be noted that separate address portions  76 X.  76 Y and verification portions  77 X,  77 Y are provided in the X and Y address buffers  75 X and  75 Y. Also, it will be noted that the control and decode logic is distributed at the memory array level in separate control blocks  70 Y. 0 ,  70 Y. 1 ,  70 X. 0  and  70 X. 1 . Signals from both the address portion  76 X and the verification portion  77 X of the address buffer  75 X are supplied to the control and verification logic  70 X. 0  and  70 X. 1 . However, only the address portion  76 .X of the X address buffer  75 X is supplied to the X decoders  72 . 0  and  72 . 1 . Similarly, signals from the address portion  76 Y and verification portion  77 Y of the Y address buffer  75 Y are supplied to the control and verification logic  70 Y. 0  and  70 Y. 1 . However, only signals from the address portion  76 Y of the Y address buffer  75 Y are supplied to Y decoders  71 . 0  and  71 . 1 . In FIG. 7, the Y decoders  71 . 0  and  71 . 1  are controlled by the Y control and verification logic  70 Y. 0  and  70 Y. 1 , respectively, for enabling the controlled output of decoded address signals to the memory banks  73 . 00 / 73 . 01  and  73 . 10 / 73 . 11 , respectively. Similarly, the X decoders  72 . 0  and  72 . 1  are controlled by control and verification logic  70 X. 0  and  70 X. 1 , respectively, for enabling the controlled output of decoded address signals to the sense and gating circuitry  78 . 00 / 78 . 10  and  78 . 01 / 78 . 11 , respectively for controlled access to the memory banks  73 . 00 / 73 . 10  and  73 . 01 / 73 . 11 , respectively. 
     A D in/D out signal is supplied from the data buffer  79  to the control and verification logic  70 Y. 0 ,  70 X. 0 ,  70 Y. 1 .  70 X. 1 . An error signal can be optionally provided on the error line  28  from the control and verification logic  70 Y. 0 ,  70 X. 0 ,  70 Y. 1  and/or  70 X. 1  where address verification is negative. 
     Accordingly, in the present example, as in the previous examples, the control and verification logic enables selective access to a memory location or locations for writing data to the location or locations, or reading data from the location or locations, where address verification is positive, and for preventing access and/or input or output of data to or from the memory locations where address verification is negative. 
     It will be appreciated that any appropriate number of memory banks for a particular memory configuration can be provided. Also, control and verification of the addresses can be provided at various levels within the memory device. Thus, for example, a combination of elements from FIGS. 6 and 7 may be provided. It should further be noted that the examples shown in FIGS. 6 and 7 are merely illustrative, and the arrangement of the control and verification logic can be provided in different ways in accordance with the desired implementation to provide address verification at an appropriate level within the memory device. 
     Indeed, it should be noted that any reasonable combinations of features from the various embodiments is possible within the scope of the present invention, these embodiments being merely presented as examples of various options within the scope of the invention. 
     Thus, merely by way of example, the direct control of the sense and gating circuitry could be provided by the distributed control and verification logic of FIG. 7, in the manner shown in FIG.  6 . 
     Also, by way of example, in any of the examples, if the data supplied to the memory device is word based, it would also be possible to include verification logic within the memory device for checking the accuracy of the data to be stored as has been described with reference to FIG.  4 . Accordingly, suitable control and verification logic could be connected to the data buffer shown in the various diagrams to verify the validity of the data on the basis of verification information (e.g. parity or ECC information) supplied with the data. 
     FIG. 8 is a schematic overview of an encapsulated memory device in accordance with the present invention. As shown in FIG. 8, the memory device  22  is encapsulated in a package  80  with a plurality of contact pins  81 , of which one pin may be for the error signal line  28 . This could be provided as a separate pin  82 , or the function of the error line could be provided with other functions on a specific pin. It should be noted that although the term pin has been used here, the device contacts could be in any suitable form, typically in a form for surface mounting, and may have any configuration appropriate to the packaging technology used. 
     An embodiment of the present invention can provide verification of addresses within memory devices and can therefore enhance the security of operation of the memory devices. As well as providing a way of checking the normal operation of a memory device, address verification in an embodiment to the present invention can also be used for verifying the performance limits of a device by, for example, increasing the speed of access to the device until errors start to occur. Also, it could enable the provision of memory devices with dynamic memory access speed, wherein, a computer system incorporating such memory devices could be configured to set the speed of operation of the memory (by adjusting the clocks to the memory) to a point just below that at which errors start to occur. 
     Although particular examples of memory devices in accordance with the present invention have been described, it will be appreciated that the present invention is not limited thereto. Many additions and/or modifications to the embodiments described are possible, including combining features from individual embodiments, as has been mentioned above. Thus, although particular embodiments of the invention have been described, many modifications/additions and/or substitutions may be made within the spirit and scope of the present invention as defined in the appended claims.