Abstract:
In an embodiment, a data scramble/descramble circuit for a memory may employ multiple scramble circuits that may provide randomization of data across both rows and columns of a memory array. The first circuit may receive at least a portion of the address of the row, and may produce an output value by logically operating on the portion of the address. The second circuit may receive the output of the first circuit (or a portion thereof) as a seed, and may scramble the data to be written to memory. In one embodiment, a least significant portion of the address may be operated upon by the first circuit (e.g. the least significant byte), which may be most likely to change from row to row as compared to other portions of the address.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention is related to memories in digital systems and, more particularly, to data randomization/scrambling mechanisms for memories. 
         [0003]    2. Description of the Related Art 
         [0004]    Certain memories used in digital systems can experience data loss if too many physically-proximate data bits in the memory have the same bit value and surround a bit of the opposite value. That is, if too many bits in physical proximity are zeros, data loss can occur for a one near the zeros. Similarly, if too many bits in physical proximity are ones, data loss can occur for a zero near the ones. More particularly, certain nonvolatile memories such as flash memories are subject to time decay in the electrical charge that represents each bit. As the charge decays, the data bit eventually cannot be reliably read (e.g. the probability of reading the same bit value that was previously written decreases). The rate of decay can increase in the memories if many nearby bits have the opposite value of the bit. To retain the data for a specified period of time, the rate of decay needs to be controlled. Accordingly, such memories specify a maximum number of nearby bits that can have the same value, as well as a lifetime for the data assuming that the maximum number is not exceeded. 
         [0005]    On the other hand, the data to be stored in the memory may actually have significant clustering of the same bit value. For example, some data may tend to have many more zero bits than one bits, or vice versa. In order to meet the required mix of zeros and ones, controllers for the memory typically implement data randomization, or data scrambling. The data randomization/scrambling mechanisms use reproducible pseudo-random modifications to change the data written to memory, and to change the data back to the original data when read from the memory. By changing the data, the mix of ones and zeros is changed in an attempt to meet the specifications. 
         [0006]    Data scrambling is applied to each row of data, seeding the pseudo-random circuitry with the address of the row. Such mechanisms result in reasonable randomization of the data in a given row. However, nearby rows are seeded with addresses that are nearly the same, and thus often receive similar randomization. Accordingly, the data along a column is not randomized very well, and thus data loss can be accelerated due to too many consecutive data bits in a column having the same value. 
       SUMMARY 
       [0007]    In an embodiment, a data scramble circuit for a memory may employ multiple scramble circuits that may provide randomization of data across both rows and columns of a memory array. The first circuit may receive at least a portion of the address of the row, and may produce an output value by logically operating on the portion of the address. The second circuit may receive the output of the first circuit (or a portion thereof) as a seed, and may scramble the data to be written to memory. In one embodiment, a least significant portion of the address may be operated upon by the first circuit (e.g. the least significant byte), which may be most likely to change from row to row as compared to other portions of the address. The multiple levels of scrambling may improve the amount of randomness in the column direction in the memory array, while the amount of randomness in the row direction may be maintained or even improved. 
         [0008]    In one embodiment, the first circuit may include circuitry to perform a logic operation on the address to produce the output. For example, the first circuit may be a cyclical redundancy check (CRC) generator. The CRC generator may receive the address (or the least significant portion, for example) and perform a CRC generation on the address. In an embodiment, the CRC generated is wider than the seed, and a portion may be used as the seed. The second circuit may be a pseudo-random number generator configured to generate a series of pseudo-random numbers based on the seed. For example, a linear feedback shift register (LFSR) may be used. The pseudo-random number may be logically combined with the data (e.g. exclusive-ORed (XORed)), and the pseudo-random number generator may be advanced to the next value after being used. Thus, the randomization of a given row (also referred to as a page) may be reproducible since the same seed would be generated for the page each time the page is opened. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following detailed description makes reference to the accompanying drawings, which are now briefly described. 
           [0010]      FIG. 1  is a block diagram of one embodiment of a system. 
           [0011]      FIG. 2  is a block diagram of one embodiment of a flash memory interface unit shown in  FIG. 1 . 
           [0012]      FIG. 3  is a block diagram of one embodiment of a data scramble unit shown in  FIG. 2 . 
           [0013]      FIG. 4  is a block diagram illustrating one embodiment of a flash memory. 
           [0014]      FIG. 5  is a flowchart illustrating operation of one embodiment of a flash memory interface unit to open a page. 
           [0015]      FIG. 6  is a flowchart illustrating operation of one embodiment of a flash memory interface unit to transfer data. 
           [0016]      FIG. 7  is a block diagram of one embodiment of a system. 
       
    
    
       [0017]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to. 
         [0018]    Various units, circuits, or other components may be described as “configured to” perform a task or tasks. In such contexts, “configured to” is a broad recitation of structure generally meaning “having circuitry that” performs the task or tasks during operation. As such, the unit/circuit/component can be configured to perform the task even when the unit/circuit/component is not currently on. In general, the circuitry that forms the structure corresponding to “configured to” may include hardware circuits. Similarly, various units/circuits/components may be described as performing a task or tasks, for convenience in the description. Such descriptions should be interpreted as including the phrase “configured to.” Reciting a unit/circuit/component that is configured to perform one or more tasks is expressly intended not to invoke 35 U.S.C. §112, paragraph six interpretation for that unit/circuit/component. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0019]    Turning now to  FIG. 1 , a block diagram of one embodiment of a system  5  is shown. In the embodiment of  FIG. 1 , the system  5  includes an integrated circuit (IC)  10  coupled to external memories  12 A- 12 B and one or more external flash memory devices  48 . In the illustrated embodiment, the integrated circuit  10  includes a central processor unit (CPU) block  14  which includes one or more processors  16  and a level 2 (L2) cache  18 . Other embodiments may not include L2 cache  18  and/or may include additional levels of cache. Additionally, embodiments that include more than two processors  16  and that include only one processor  16  are contemplated. The integrated circuit  10  further includes a set of one or more non-real time (NRT) peripherals  20  and a set of one or more real time (RT) peripherals  22 . In the illustrated embodiment, the CPU block  14  is coupled to a bridge/direct memory access (DMA) controller  30 , which may be coupled to one or more peripheral devices  32  and/or one or more peripheral interface controllers  34 . The number of peripheral devices  32  and peripheral interface controllers  34  may vary from zero to any desired number in various embodiments. One example of a peripheral device/interface controller is the flash memory interface unit  46 , coupled to the bridge/DMA unit  30  and the flash memory devices  48 . The system  5  illustrated in  FIG. 1  further includes a graphics unit  36  comprising one or more graphics controllers such as G 0   38 A and G 1   38 B. The number of graphics controllers per graphics unit and the number of graphics units may vary in other embodiments. As illustrated in  FIG. 1 , the system  5  includes a memory controller  40  coupled to one or more memory physical interface circuits (PHYs)  42 A- 42 B. The memory PHYs  42 A- 42 B are configured to communicate on pins of the integrated circuit  10  to the memories  12 A- 12 B. The memory controller  40  also includes a set of ports  44 A- 44 E. The ports  44 A- 44 B are coupled to the graphics controllers  38 A- 38 B, respectively. The CPU block  14  is coupled to the port  44 C. The NRT peripherals  20  and the RT peripherals  22  are coupled to the ports  44 D- 44 E, respectively. The number of ports included in a memory controller  40  may be varied in other embodiments, as may the number of memory controllers. The number of memory PHYs  42 A- 42 B and corresponding memories  12 A- 12 B may be one or more than two in other embodiments. 
         [0020]    The flash memory interface unit  46  may include circuitry configured to receive read and write memory operations for the flash memory devices  48 , and configured to interface to the flash memory devices  48  to complete the read/write operations. In one embodiment, the read/write requests may be sourced from the bridge/DMA controller  30 . The flash memory interface unit  46  may be programmable via one or more control registers (see  FIG. 2  described below) to perform memory transfers to/from the flash memory devices  48 . For example, the control registers may be programmable via programmed input/output (PIO) operations from the processors  16  or other processors in the system  5 . The PIO operations may pass through the bridge/DMA controller  30  to the flash memory interface unit  46 . Flash memory devices  40  may be flash memory, a type of non-volatile memory that is known in the art. In other embodiments, other forms of non-volatile memory may be used. For example, various types of programmable ROMs such as electrically-erasable programmable ROMs (EEPROMs), etc. may be used. 
         [0021]    The flash memory interface unit  46  may implement the data scramble unit mentioned previously. That is, the flash memory interface unit  46  may include a data scramble unit that includes a first circuit and a second circuit. The first circuit may be configured to operate on at least a portion of the address of the memory operation, producing an output value that may be used as a seed to the second circuit. The second circuit may be configured to generate pseudo-random numbers that may be used to scramble the data to be written to memory, or descramble the data that is read from memory. 
         [0022]    In one embodiment, the first circuit may be a cyclical redundancy check (CRC) generator. The CRC generator may receive the address (or the least significant portion, for example) and perform a CRC generation. The second circuit may be a pseudo-random number generator configured to generate a series of pseudo-random numbers based on the seed. For example, a linear feedback shift register (LFSR) may be used. The pseudo-random number may be logically combined with the data (e.g. exclusive-ORed (XORed)), and the pseudo-random number generator may be advanced to the next value after being used. 
         [0023]    The flash memory interface unit  46  may be programmed via PIO operations to perform memory transfers to/from the flash memory devices  48 . For write operations, the bridge/DMA controller  30  may DMA the write data to the flash memory interface unit  46 . For read operations, the bridge/DMA controller  30  may DMA the read data from the flash memory interface unit  46 . In an embodiment, the flash memory devices  46  may support a page of data transfer to/from the devices. The size of the page is device-dependent, and may not be the same as the page size used for virtual-to-physical address translation for the memory  12 . For example, page sizes of 512 bytes, 2048 bytes, and 4096 bytes are often used. 
         [0024]    Returning to the memory controller  40 , generally a port may be a communication point on the memory controller  40  to communicate with one or more sources. In some cases, the port may be dedicated to a source (e.g. the ports  44 A- 44 B may be dedicated to the graphics controllers  38 A- 38 B, respectively). In other cases, the port may be shared among multiple sources (e.g. the processors  16  may share the CPU port  44 C, the NRT peripherals  20  may share the NRT port  44 D, and the RT peripherals  22  such as the display pipes  26  and the image processor  24  may share the RT port  44 E. Each port  44 A- 44 E is coupled to an interface to communicate with its respective agent. The interface may be any type of communication medium (e.g. a bus, a point-to-point interconnect, etc.) and may implement any protocol. In some embodiments, the ports  44 A- 44 E may all implement the same interface and protocol. In other embodiments, different ports may implement different interfaces and/or protocols. In still other embodiments, the memory controller  40  may be single ported. 
         [0025]    In an embodiment, each source may assign a quality of service (QoS) parameter to each memory operation transmitted by that source. The QoS parameter may identify a requested level of service for the memory operation. Memory operations with QoS parameter values requesting higher levels of service may be given preference over memory operations requesting lower levels of service. The memory controller  40  may be configured to process the QoS parameters received on each port  44 A- 44 E and may use the relative QoS parameter values to schedule memory operations received on the ports with respect to other memory operations from that port and with respect to other memory operations received on other ports. In some embodiments, the memory controller  40  may be configured to upgrade QoS levels for pending memory operations. Various upgrade mechanism may be supported. For example, the memory controller  40  may be configured to upgrade the QoS level for pending memory operations of a flow responsive to receiving another memory operation from the same flow that has a QoS parameter specifying a higher QoS level. This form of QoS upgrade may be referred to as in-band upgrade, since the QoS parameters transmitted using the normal memory operation transmission method also serve as an implicit upgrade request for memory operations in the same flow. The memory controller  40  may be configured to push pending memory operations from the same port or source, but not the same flow, as a newly received memory operation specifying a higher QoS level. As another example, the memory controller  40  may be configured to couple to a sideband interface from one or more agents, and may upgrade QoS levels responsive to receiving an upgrade request on the sideband interface. In another example, the memory controller  40  may be configured to track the relative age of the pending memory operations. The memory controller  40  may be configured to upgrade the QoS level of aged memory operations at certain ages. The ages at which upgrade occurs may depend on the current QoS parameter of the aged memory operation. 
         [0026]    The memory controller  40  may be configured to determine the memory channel addressed by each memory operation received on the ports, and may be configured to transmit the memory operations to the memory  12 A- 12 B on the corresponding channel. The number of channels and the mapping of addresses to channels may vary in various embodiments and may be programmable in the memory controller. The memory controller may use the QoS parameters of the memory operations mapped to the same channel to determine an order of memory operations transmitted into the channel. 
         [0027]    The processors  16  may implement any instruction set architecture, and may be configured to execute instructions defined in that instruction set architecture. The processors  16  may employ any microarchitecture, including scalar, superscalar, pipelined, superpipelined, out of order, in order, speculative, non-speculative, etc., or combinations thereof. The processors  16  may include circuitry, and optionally may implement microcoding techniques. The processors  16  may include one or more level 1 caches, and thus the cache  18  is an L2 cache. Other embodiments may include multiple levels of caches in the processors  16 , and the cache  18  may be the next level down in the hierarchy. The cache  18  may employ any size and any configuration (set associative, direct mapped, etc.). 
         [0028]    The graphics controllers  38 A- 38 B may be any graphics processing circuitry. Generally, the graphics controllers  38 A- 38 B may be configured to render objects to be displayed into a frame buffer. The graphics controllers  38 A- 38 B may include graphics processors that may execute graphics software to perform a part or all of the graphics operation, and/or hardware acceleration of certain graphics operations. The amount of hardware acceleration and software implementation may vary from embodiment to embodiment. 
         [0029]    The NRT peripherals  20  may include any non-real time peripherals that, for performance and/or bandwidth reasons, are provided independent access to the memory  12 A- 12 B. That is, access by the NRT peripherals  20  is independent of the CPU block  14 , and may proceed in parallel with CPU block memory operations. Other peripherals such as the peripheral  32  and/or peripherals coupled to a peripheral interface controlled by the peripheral interface controller  34  may also be non-real time peripherals, but may not require independent access to memory. Various embodiments of the NRT peripherals  20  may include video encoders and decoders, scaler/rotator circuitry, image compression/decompression circuitry, etc. 
         [0030]    The RT peripherals  22  may include various peripherals that exhibit real-time characteristics. For example, the RT peripherals may include one or more image processors and one or more display pipes. The display pipes  26  may include circuitry to fetch one or more image frames and to blend the frames to create a display image. The display pipes may further include one or more video pipelines, and video frames may be blended with (relatively) static image frames to create frames for display at the video frame rate. The result of the display pipes may be a stream of pixels to be displayed on the display screen. The pixel values may be transmitted to a display controller for display on the display screen. The image processor may receive camera data and process the data to an image to be stored in memory. 
         [0031]    The bridge/DMA controller  30  may comprise circuitry to bridge the peripheral(s)  32  and the peripheral interface controller(s)  34  to the memory space. In the illustrated embodiment, the bridge/DMA controller  30  may bridge the memory operations from the peripherals/peripheral interface controllers through the CPU block  14  to the memory controller  40 . The CPU block  14  may also maintain coherence between the bridged memory operations and memory operations from the processors  16 /L2 Cache  18 . The L2 cache  18  may also arbitrate the bridged memory operations with memory operations from the processors  16  to be transmitted on the CPU interface to the CPU port  44 C. The bridge/DMA controller  30  may also provide DMA operation on behalf of the peripherals  32  and the peripheral interface controllers  34  to transfer blocks of data to and from memory. More particularly, the DMA controller may be configured to perform transfers to and from the memory  12 A- 12 B through the memory controller  40  on behalf of the peripherals  32  and the peripheral interface controllers  34 . The DMA controller may be programmable by the processors  16  to perform the DMA operations. For example, the DMA controller may be programmable via descriptors. The descriptors may be data structures stored in the memory  12 A- 12 B that describe DMA transfers (e.g. source and destination addresses, size, etc.). Alternatively, the DMA controller may be programmable via registers in the DMA controller (not shown). 
         [0032]    The peripherals  32  may include any desired input/output devices or other hardware devices that are included on the integrated circuit  10 . For example, the peripherals  32  may include networking peripherals such as one or more networking media access controllers (MAC) such as an Ethernet MAC or a wireless fidelity (WiFi) controller. An audio unit including various audio processing devices may be included in the peripherals  32 . One or more digital signal processors may be included in the peripherals  32 . The peripherals  32  may include any other desired functional such as timers, an on-chip secrets memory, an encryption engine, etc., or any combination thereof. 
         [0033]    The peripheral interface controllers  34  may include any controllers for any type of peripheral interface. For example, the peripheral interface controllers may include various interface controllers such as a universal serial bus (USB) controller, a peripheral component interconnect express (PCIe) controller, general purpose input/output (I/O) pins, etc. 
         [0034]    The memories  12 A- 12 B may be any type of memory, such as dynamic random access memory (DRAM), synchronous DRAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.) SDRAM (including mobile versions of the SDRAMs such as mDDR3, etc., and/or low power versions of the SDRAMs such as LPDDR2, etc.), RAMBUS DRAM (RDRAM), static RAM (SRAM), etc. One or more memory devices may be coupled onto a circuit board to form memory modules such as single inline memory modules (SIMMs), dual inline memory modules (DIMMs), etc. Alternatively, the devices may be mounted with the integrated circuit  10  in a chip-on-chip configuration, a package-on-package configuration, or a multi-chip module configuration. 
         [0035]    The memory PHYs  42 A- 42 B may handle the low-level physical interface to the memory  12 A- 12 B. For example, the memory PHYs  42 A- 42 B may be responsible for the timing of the signals, for proper clocking to synchronous DRAM memory, etc. In one embodiment, the memory PHYs  42 A- 42 B may be configured to lock to a clock supplied within the integrated circuit  10  and may be configured to generate a clock used by the memory  12 . 
         [0036]    It is noted that other embodiments may include other combinations of components, including subsets or supersets of the components shown in  FIG. 1  and/or other components. While one instance of a given component may be shown in  FIG. 1 , other embodiments may include one or more instances of the given component. Similarly, throughout this detailed description, one or more instances of a given component may be included even if only one is shown, and/or embodiments that include only one instance may be used even if multiple instances are shown. 
         [0037]    Turning now to  FIG. 2 , a block diagram of one embodiment of the flash memory interface unit  46  is shown. In the illustrated embodiment, the flash memory interface unit  46  includes a command FIFO  50 , a flash memory interface (FMI) control circuit  52 , a macro memory  54 , an operand FIFO  56 , a flash memory controller (FMC)  58 , a set of FMC control registers  60 , data buffers  62 A- 62 B, an error checking/correction (ECC) unit  64 , and a data scramble unit  66 . The command FIFO  50 , FMI control circuit  52 , macro memory  54 , operand FIFO  56 , and buffers  62 A- 62 B are all coupled to an internal interface to the bridge/DMA controller  30 . The FMI control circuit  52  is further coupled to the command FIFO  50 , the macro memory  54 , the operand FIFO  56 , and the FMC control registers  60 . The FMC control registers  60  are further coupled to the FMC  58  and the data scramble unit  66 . The FMC  58  is coupled to an external interface to the flash memory devices  48 . The FMC  58  is further coupled to the data scramble unit  66 , which is further coupled to the buffers  62 A- 62 B. The ECC unit  64  is also coupled to the buffers  62 A- 62 B. 
         [0038]    The FMC control registers  60  may be programmed with commands to open a page of one of the flash memory devices  48 , and to transfer data into or out of the page. The commands include the address of the page, at least a portion of which may be received by the data scramble unit  66 . In the illustrated embodiment, the commands may be written to the command FIFO  50  and performed by the FMI control circuit  52 . In other embodiments, the commands may be written directly to the registers  60  or the commands may be received by the FMC  58  directly. In still other embodiments, a combination of direct commands and commands in the registers  60  may be used. 
         [0039]    The data scramble unit  66  may be configured to operate on the received address and to seed the pseudo-random number generator, which may be configured to generate a series of pseudo-random numbers beginning with the seed. The data scramble unit  66  may be configured to logically combine the pseudo-random numbers with the data to scramble the data on a write operation (e.g. by XORing the data and the pseudo-random number). On a read operation, the data scramble has the effect of descrambling, since the data read from the flash memory  48  was scrambled prior to writing the data. 
         [0040]    Generally, data scrambling may refer to any deterministic, reversible modification of the data. The data scrambling may be designed to increase the variation in the data, reducing the number of consecutive zeros or consecutive ones in the data, on average. Data scrambling may also be referred to as data randomization. In this context, randomization may be pseudo-random, because the randomization/scrambling is reproducible so that the original data can be recovered. A series of pseudo-random numbers, for example, may appear to be random (there may be large and varied distances between consecutive numbers, the repeat rate in the numbers may be low, etc.). However, the series is deterministic and, given the same seed, the same series pseudo-random numbers are generated in the same order. 
         [0041]    The FMI control circuit  52  may be configured to receive PIO operations from the bridge/DMA controller  30 . Some PIO operations may be directed to the command FIFO  50 , the macro memory  54 , or the operand FIFO  56 . For example, PIO writes may be used to write commands into the command FIFO  50 , to download macros into the macro memory  54 , or to write operands into the operand FIFO  56 . Addresses may be assigned to each of the FIFO  50 , the macro memory  54 , and the operand FIFO  56 , which may be used in the PIO operands to address the desired resource. For example, the FIFOs  50  and  56  may have a single assigned address since they may operate in a first-in, first-out manner. A PIO write to the address may cause the FMI control circuit  52  to store the data provided with the write in the next open entry in the FIFO  50  or  56 . That is, the data may be appended to the tail of the FIFO  50  or  56 , where commands or operands are removed from the head of the FIFO  50  or  56 . The macro memory  54  may have a range of addresses assigned to it, e.g. an address per word of the macro memory  54 . PIO writes to the addresses may store the provided data word into the addressed word of the macro memory  54 . 
         [0042]    The FMI control circuit  52  may process the commands in the command FIFO  50  to program various FMC control registers  60  to cause the FMC  58  to perform a particular memory transfer to/from the flash memory devices  48 . In one embodiment, the FMC  58  is configured to receive relatively low-level control via the FMC control registers  60 , including address, chip enables, transfer commands, etc. Commands in the command FIFO  50  may be interpreted by the FMI control circuit  52  and the corresponding FMC control registers  60  may be written by the FMI control circuit  52 . Similarly, commands to wait for an event may be interpreted by the FMI control circuit  52  to read one or more FMC control registers  60  to detect the event. There may also be direct control signals between the FMI control circuit  52  to the FMC  58 , in some embodiments (not shown in  FIG. 2 ) which may be driven by the FMI control circuit  52  responsive to commands and/or monitored by the FMI control circuit  52  responsive to commands. 
         [0043]    A macro command may be in the command FIFO  50 , and the FMI control circuit  52  may perform commands from the macro memory  54  in response to the macro command. In other embodiments, the macro command may be transmitted as a PIO operation to the FMI control circuit  52 . In still other embodiments, macro commands may be encountered in the command FIFO  50  or in PIO operations. The macro command may include a starting address in the macro memory and a word count indicating the number of words to read from the macro memory  54 . The FMI control circuit  52  may perform the commands in the macro prior to reading the next command in the command FIFO  50 . The words in the macro may include operands in addition to commands, in one embodiment. Other embodiments may use a command count rather than a word count. The macro command may also include a loop count and the macro may be iterated the number of times indicated by the loop count. Reading words from the command FIFO  40  and the operand FIFO  56  may include the FMI control circuit  52  deleting those words from the FIFO. Reading words from the macro memory  54 , on the other hand, may not involve deleting the words so that macros may be repeatedly performed. 
         [0044]    The FMC  58  may perform memory transfers in response to the contents of the FMC control registers  60 , transmitting data read from the flash memory devices  48  to the data scramble unit  66 , which may descramble the data and write the descrambled data to the buffers  62 A- 62 B. Furthermore, the FMC may write data provided by the data scramble unit  66  (corresponding to data read from the buffers  62 A- 62 B) to the flash memory devices  48 . The buffers  62 A- 62 B may be used in a ping-pong fashion, in which one of the buffers  62 A- 62 B is being filled with data while the other is being drained. For example, reads from the flash memory devices  48  may include the filling one of the buffers  62 A- 62 B while the other buffer  62 A- 62 B is being drained by the bridge/DMA controller  30  performing DMA operations to memory  12 . Writes to the flash memory devices  48  may include the bridge/DMA controller  30  filling one of the buffers  62 A- 62 B with data while the FMC  58  drains the other buffer  62 A- 62 B. The ECC unit  64  may generate ECC data for writes to the flash memory devices  48 , and may check the ECC data for reads from the flash memory devices  48 . 
         [0045]    Commands in the command queue and/or commands in the macro memory may use operands to control their operation. In some cases, the operands may be stored in the command FIFO  50 . In other cases, the operands may be stored in the operand FIFO  56 . Commands in the command FIFO  50  or in the macro memory  54  may specify that the flash memory interface unit  46  load operands from the operand FIFO  56  and operate on the operands. The operand FIFO  56  may be used with a macro to supply instance-specific data for the generic macro (e.g. flash memory addresses, chip enables, etc.). 
         [0046]    It is noted that, while the data scramble unit  66  is described in this embodiment for use in a flash memory interface unit, other memory interface units/memory controllers configured to interface to other memories may implement the data scramble unit  66 . 
         [0047]    Turning now to  FIG. 3 , a block diagram of one embodiment of the data scramble unit  66  is shown. In the illustrated embodiment, the data scramble unit  66  includes a CRC generator  70 , a CRC register  72 , an LFSR control circuit  74 , an LFSR register  76 , and a circuit  78 . Together, the LFSR control circuit  74  and the LFSR register  76  may form an LFSR. The CRC generator  70  may be coupled to receive a portion of the page address from the FMC control registers  60  (e.g. the least significant byte, FMA[7:0] in  FIG. 3 ) and may be coupled to the CRC register  72  and the LFSR control circuit  74 . The LFSR control circuit  74  may be further coupled to the LFSR register  76  and the CRC register  72 . The LFSR register  76  may further be coupled to the circuit  78 . The circuit  78  may comprise bitwise XOR circuitry, represented by the XOR gate  80  for write data and the XOR gate  82  for read data. 
         [0048]    The CRC generator  70  may be configured to generate a CRC responsive to the received address, may be configured to store the generated CRC in the CRC register  72 . In other embodiments, the CRC register  72  may not be used and the CRC generator  70  may output the generated CRC directly to the LFSR control circuit  74 . In the illustrated embodiment, the CRC generator  70  may be configured to generate a 64 bit CRC, 32 bits of which are used as a seed for the LFSR. More generally, the generated CRC may be larger than the page address (which may be 32 bits in this embodiment) and/or larger than the width of the data transferred on the interface to the flash memory devices  48  (which may also be 32 bits in this embodiment). Other embodiments may employ different address/data widths and different CRC widths. Generally, the CRC width may be selected to be larger than the address/data width. 
         [0049]    Employing a larger CRC width than the address, and using the least significant bits of the address, may provide more variation in the LFSR seed between consecutive addresses within the flash memory devices. Greater variation in the LFSR seed may create greater variation in the numbers generated by the LFSR, which may result in greater variation in the data that is written to consecutive rows with the flash memory. Data from consecutive rows may be physically near each other, and providing greater variation may improve the life of data in the consecutive rows in some embodiments. 
         [0050]    The CRC generator  70  may be configured to form a larger input value to the CRC generation itself using the received address bits. For example, in an embodiment, multiple copies of the received address bits may be concatenated to form the input value. One or more of the copies may be inverted and concatenated. For example, an embodiment may use four copies of the input address byte to form a 32-bit CRC input value. Thus, the input value to the CRC generation may have a width that is an integer multiple of the width of the portion of the input address. In one particular embodiment, the second least significant byte of the CRC input may be an inverted copy of the input address byte, and other copies may not be inverted. That is, the input CRC value may be:
       Input CRC[31:0]={FMA[7:0], FMA[7:0], ˜FMA[7:0], FMA[7:0]}
 
Other embodiments may use other combinations of inverted and non-inverted copies, as desired. While the least significant byte of the page address is used in the present embodiment, other embodiments may use other portions of the address (e.g. the least significant two or three bytes, or non-byte-sized bit fields from the address). An inverted copy of a value may also be referred to as a complement of the value.
       
 
         [0052]    In one embodiment, the CRC generator  70  may implement CRC-64-ECMA-182. This CRC may be designed for large data sets, and may provide a low repeat rate. Other embodiments may implement any desired CRC. The polynomial for CRC-64-ECMA-182 is x 64 +x 62 +x 57 +x 55 +x 54 +x 53 +x 52 +x 47 +x 46 +x 45 +x 40 +x 39 +x 38 +x 37 +x 35 +x 33 +x 32 +x 31 +x 29 +x 27 +x 24 +x 23 +x 22 +x 21 +x 19 +x 17 +x 13 +x 12 +x 10 +x 9 +x 7 +x 4 +x+1. The CRC may be initialized as all one&#39;s, and then the CRC may be generated over the CRC input value. 
         [0053]    The least significant bits of the generated CRC (e.g. the least significant 32 bits of the CRC, in this embodiment) may be used as the seed to the LFSR. The CRC generator  70  may generate the CRC, and may assert the load seed signal to the LFSR control circuit  74 . The LFSR control circuit  74  may initialize the LFSR register  72  to the seed. Responsive to the seed, the LFSR may generate a series of pseudo-random numbers. More particularly, the seed may be used as the first pseudo-random number. As each pseudo-random number is consumed by the circuit  78 , randomizing data to/from the page, the LFSR may generate the next number in the series. 
         [0054]    Generally, the current value of the LFSR may be used to generate a bit that is shifted into the LFSR to create the next value. For example, the LFSR may be configured to right shift by one bit, shifting the newly generated bit into the least significant bit of the next value. The LFSR may, for example, be configured to generate the new bit as the XOR of the selected bits. Any mechanism may be used in various embodiments. For example, an embodiment may implement the following polynomial: x 32 +x 24 +x 21 +x 6 +x 2 +x 1 +1. Other embodiments may implement other polynomials. Generating the bit and shifting the register may generally be referred to as advancing the LFSR to the next value. 
         [0055]    The circuit  78  may receive the LFSR value, and may be configured to bitwise XOR the LFSR value with the read or write data. In an embodiment, the LFSR value may be the same width as the width of one data transfer (or beat) to/from the flash memory devices (e.g. 32 bits in this embodiment). In other embodiments, the data interface may be wider than the LFSR value and the LFSR value may be concatenated with itself to create a wide enough value to be bitwise-combined with the data. Generally, any width of data transfer/beat may be used in various embodiments. Each data transfer/beat may be one cycle (e.g. one clock cycle, for single data rate memory, one half clock cycle, for double data rate, etc.) of data transfer. Thus, a page may be transferred as multiple data transfers/beats in this embodiment. 
         [0056]    Since the same seed is generated for both a read and a write to the page, the same set of pseudo-random numbers may be generated as the page is read and as the page is written. Thus, the bitwise XOR of the read data with the pseudo-random numbers may unscramble the data that was scrambled to write the data to the flash memory devices, recovering the original data that was provided for storage in the flash memory device. 
         [0057]    Turning now to  FIG. 4 , a block diagram of one embodiment of a flash memory array  90  is shown. The array  90  may include multiple rows, one for each page of the flash memory array. Each row may include N bits (bits  0  to N−1). The bits of adjacent rows in the array  90  may be located physically near other bits. Thus, for example, bit  1  of page 1 may be physically near bits  0  and  2  of page 1, and bits  0  to  2  of pages 0 and 2 as well. Using the mechanisms described above for data scrambling, good variation in bits of a column of the memory (e.g. bits in adjacent rows having the same bit number) may be achieved. 
         [0058]      FIG. 5  is a flowchart illustrating operation of one embodiment of the FMI unit  46 , and more particularly the data scramble unit  66 , is shown for an open page command. While the blocks are shown in a particular order in  FIG. 5  for ease of understanding, other orders may be used. Blocks may be performed in parallel by combinatorial logic circuitry in the FMI unit  46 /data scramble unit  66 . Blocks, combinations of blocks, and/or the flowchart as a whole may be pipelined over multiple clock cycles. The FMI unit  46 /data scramble unit  66  may be configured to implement the operation shown in  FIG. 5 . The open page command may be specified as a command in the control registers  60 . 
         [0059]    The data scramble unit  66  may receive the page address (or the portion thereof, such as the least significant byte in the embodiment of  FIG. 3 ) (block  92 ). Responsive to the received address, the data scramble unit  66  may generate the CRC (block  94 ). The data scramble unit  66  may load the generated CRC (or the least significant portion, in the embodiment of  FIG. 3 ) into the LFSR as the seed (block  96 ). 
         [0060]      FIG. 6  is a flowchart illustrating operation of one embodiment of the FMI unit  46 , and more particularly the data scramble unit  66 , is shown for a data transfer to/from the flash memory devices. The transfer may be either a read or write, for data that is part of a page read or a page write operation. While the blocks are shown in a particular order in  FIG. 6  for ease of understanding, other orders may be used. Blocks may be performed in parallel by combinatorial logic circuitry in the FMI unit  46 /data scramble unit  66 . Blocks, combinations of blocks, and/or the flowchart as a whole may be pipelined over multiple clock cycles. The FMI unit  46 /data scramble unit  66  may be configured to implement the operation shown in  FIG. 6 . The data transfer command may be specified as a command in the control registers  60 . 
         [0061]    The data scramble unit  66  may XOR the LFSR data with the transferred data (block  100 ) and may transmit the resulting modified (scrambled) data to the receiver (block  102 ). The receiver may be a buffer  62 A- 62 B for a read, or the FMC  58  (and ultimately the flash memory devices) for a write. The data scramble unit  66  may advance the LFSR to the next value (block  104 ). 
         [0062]    Turning next to  FIG. 7 , a block diagram of one embodiment of a system  350  is shown. In the illustrated embodiment, the system  350  includes at least one instance of the integrated circuit  10  coupled to external memory  12  (e.g. the memory  12 A- 12 B in  FIG. 1 ). The integrated circuit  10  is coupled to one or more peripherals  354  and the external memory  12 . A power supply  356  is also provided which supplies the supply voltages to the integrated circuit  10  as well as one or more supply voltages to the memory  12  and/or the peripherals  354 . In some embodiments, more than one instance of the integrated circuit  10  may be included (and more than one external memory  12  may be included as well). The flash memory devices  48  are also shown in the system  350 , coupled to the IC  10 . 
         [0063]    The peripherals  354  may include any desired circuitry, depending on the type of system  350 . For example, in one embodiment, the system  350  may be a mobile device (e.g. personal digital assistant (PDA), smart phone, etc.) and the peripherals  354  may include devices for various types of wireless communication, such as wifi, Bluetooth, cellular, global positioning system, etc. The peripherals  354  may also include additional storage, including RAM storage, solid state storage, or disk storage. The peripherals  354  may include user interface devices such as a display screen, including touch display screens or multitouch display screens, keyboard or other input devices, microphones, speakers, etc. In other embodiments, the system  350  may be any type of computing system (e.g. desktop personal computer, laptop, workstation, net top etc.). 
         [0064]    Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.