System on a chip having a non-volatile imperfect memory

A system-on-a-chip is described herein. The system-on-a-chip includes a microprocessor, a non-volatile imperfect semiconductor memory device and a memory controller. The memory controller is configured to transfer device data between the microprocessor and the non-volatile semiconductor imperfect memory device.

BACKGROUND OF THE INVENTION

Mobile electronic devices, such as digital cameras, personal digital assistants (PDA's), and cell phones continue to increase in popularity. Such portable devices are commonly manufactured using application specific integrated circuit (ASIC) designs. Conventional ASIC design involves development of medium complexity integrated circuits (ICs) essentially comprising core logic and some hard macros, such as on-chip static random access memories (SRAMs). However, as semiconductor processing technology continues to advance, more complicated IC designs have evolved, such as system-on-chip (SoC) designs.

A continuing trend is to manufacture mobile electronic devices utilizing SoC designs. However, while often referred to as SoC devices, conventional SoC-based mobile electronic devices continue to utilize memory devices that are not part of the SoC. These “off-chip” memory devices can be broadly categorized as either removable or non-removable devices.

Non-removable memory devices typically comprise volatile memory devices, such as SRAM or dynamic random access memory (DRAM) devices, which are located on a printed circuit board (PCB) along with the associated SoC. Such memory have a high degree of reliability, with each bit basically being guaranteed as “good” by manufacturers, which has led to these devices sometimes being referred to as “perfect” memory devices. These so-called perfect memory devices do not require error correction means, and thus greatly simplify the design and reduce the cost of any memory control/interface circuitry internal to the SoC. However, the memory devices themselves can be expensive and can potentially consume large amounts of limited battery capacity.

Removable memory devices are generally some type non-volatile flash memory device used for data storage and typically comprise some type of removable form factor card, such as a CompactFlash (CF) or Smart Media card. Memory cards provide flexibility as to the memory requirements of an individual user and remove the cost of the memory device from the initial cost of the mobile electronic device, thus making them more attractive to consumers. However, while the cost of the memory device itself is eliminated, removable memory devices require costly interface circuitry. In addition to expensive physical interface connections between the device and the memory card, such as the male/female pin configuration of a CF card, some SoC-based mobile electronic devices continue to utilize a separate memory controller chip to support the addressing/error correction required to support communication between the SoC and the memory card. Additionally, the memory controller and physical interface are essentially duplicated as part of the removable memory card, further raising the ultimate cost of the device to a consumer. Also, while continually being increased, the storage capacities of these devices is still relatively limited as driven by cost and/or space concerns.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a system-on-a-chip having, a microprocessor, a non-volatile imperfect semiconductor memory device and a memory controller. The memory controller is configured to transfer device data between the microprocessor and the non-volatile semiconductor imperfect memory device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a block diagram illustrating a mobile computing device30utilizing one exemplary embodiment of a system-on-a-chip (SoC)32according to the present invention. A mobile computing device is defined as a portable microprocessor-based electronic device. Examples of a mobile computing device include a notebook computer, a laptop computer, a tablet PC, a personal digital assistant or wireless phone.

SoC32comprises a processor34, a memory controller36, and a non-volatile semiconductor-based imperfect (NSVBI) memory device40incorporated onto a same silicon stack. Memory controller36is coupled to Soc processor34via a first control path38and to non-volatile semiconductor-based imperfect memory device40via a second control path42. An imperfect memory device is herein defined as a high-density semiconductor-based memory device that, in addition to having permanent errors, will periodically have a random memory bit that is temporarily in error, and thus require some type of error correction and/or memory mapping in order to provide reliable data storage. Examples of such an imperfect memory devices are ARS (Atomic Resolution Storage) and MRAM (magnetic random access memory) devices.

In one embodiment, non-volatile semiconductor-based imperfect memory device40is external to SoC32and connectable to memory controller36via second control path42. In one embodiment, SoC32and the external non-volatile semiconductor-based imperfect memory device40are part of a single printed circuit board39.

Memory controller36is configured to receive from and send to SoC processor34via first control path38at least one data block having an associated logical block address. Memory controller36is further configured to translate the associated logical block address to a corresponding physical block address, and to provide for the at least one data block an error correction code (ECC) that is a function of the at least one data block. Memory controller36is further configured to send to and to receive from non-volatile semiconductor-based imperfect memory device40via data path42the at least one data block and corresponding ECC using the corresponding physical block address. Memory controller36also provides error detection/correction for the at least one data block based on the at least one data block and ECC received from non-volatile semiconductor-based imperfect (NVSBI) memory device40to thereby provide processor34with substantially reliable read/write access to NVSBI memory device40.

In one embodiment, imperfect memory controller36is configured to support the transfer of data between SoC processor34and imperfect memory device40, wherein imperfect memory device40is an ultra-high density ARS device. ARS is an emerging technology based on using a field emitter to generate a beam of electrons to change a state of a storage area in a storage medium, wherein the state of the storage area is representative of the stored information. One such memory device is described in Gibson et al. U.S. Pat. No. 5,557,596, incorporated herein by reference.

Gibson describes a storage device having a plurality of field emitters in close proximity to a storage medium, and a micromover. The storage medium has a plurality of storage areas, and the field emitters are spaced apart so that one field emitter is responsible for a sub-plurality of storage areas on the storage medium. Each storage area can be in one of a few different states, but binary information is stored with one state representing a high bit and another state representing a low bit. When a field emitter bombards a storage area with an electron beam, a signal current is generated. The magnitude of the signal current depends on the state of the storage area. Thus, the information contained in the storage area can be read by measuring the signal current. The magnitude of each electron beam can be increased to a pre-selected level to change the state of the storage area on which it impinges. Thus, information can be written on the storage areas by using the electron beams to change the state a storage area.

Both the field emitters and the micromover are made using semiconductor microfabrication techniques. The micromover scans the storage medium with respect to the emitters or vice versa. In this way, each emitter can access information from a plurality of storage areas on the medium. By using hundreds or thousands of field emitters reading and/or writing in parallel, ARS storage devices, in addition to providing ultra-high storage densities, can potentially provide very fast access times and data rates.

In one embodiment, imperfect memory controller36is configured to support the transfer of data between SoC processor34and imperfect memory device40, wherein imperfect memory device40is magnetic random access memory device (MRAM). MRAM is an emerging memory technology that utilizes magnetic domains rather than electrical charges, as used by DRAM, SRAM, and flash memory, for storage of data. MRAM devices have many potential advantages such as being faster and using less battery power than currently utilized forms of electronic memory while providing equal, and potentially greater, storage density. One suitable MRAM device is described in “Lower Power MRAM Memory Array”, U.S. Pat. No. 6,466,471, incorporated herein by reference.

A typical MRAM device comprises a plurality of conductive traces referred to as word lines and bit lines routed across an array of memory cells. Word lines extend along rows of the memory cell array and bit lines extend along columns of the memory cell array. Memory cells are located at a cross point of each work line and bit line. Memory cells may be of different types, such as a magnetic tunnel junction (MJT) memory cell or a giant magnetoresistive (GMR) memory cell. Generally, the magnetic memory cell includes a first layer of magnetic film in which the orientation of magnetization if alterable and a second layer of magnetic film in which the orientation of magnetization may be fixed or “pinned” in a particular direction. The magnetic film having alterable magnetization is referred to as a sense layer or data storage layer and the magnetic film layer that is fixed is referred to as a reference layer or a pinned layer.

Each memory cell stores a bit of information as an orientation of magnetization in the sense layer. The magnetization orientation of a selected memory cell is switched by supply currents provided to the word line and bit line that cross at the selected memory cell. The currents create magnetic fields that, when combined, switch the magnetization orientation of the sense layer from parallel to anti-parallel with respect to the orientation of magnetization of the reference layer, or vice versa. These two stable orientations, parallel and anti-parallel, respectively represent the binary logic values of “1” and “0.”

The resistance through the memory cell differs according to whether the orientation of magnetization of the sense layer and the reference layer is parallel or anti-parallel. This resistance is highest when the orientation is anti-parallel (logic state “0”) and lowest when the orientation is parallel (logic state “1”). Thus, the state of the memory cell can be determined by sensing the resistance of the memory cell.

By integrating memory controller36and non-volatile semiconductor-based imperfect memory device40onto SoC32, SoC processor34is able to read/write data directly to NVSBI memory device40without the need for costly physical electrical interconnections (i.e., male-female pin connectors), a separate memory device (i.e., CompactFlash memory card), and/or a separate memory controller chip.

FIG. 2is a block diagram illustrating one exemplary embodiment of on-chip memory controller36according to the present invention. Memory controller36includes a buffer manager50, a processor translator52, a buffer memory54, a memory translator56, and a memory interface58. Buffer manager50further includes a plurality of “set-up” registers60.

Buffer manager50comprises hardware-implemented logic configured to manage data transfer between SoC processor34and imperfect memory device40by coordinating access to buffer memory52. Buffer manager50enables SoC processor34to write/read data to/from one location within buffer memory52while data is concurrently being written to/from imperfect memory device40from/to another location within buffer memory52.

Buffer50is coupled to SoC processor34via a control data path64. In one embodiment, control path64is utilized by SoC processor34to communicate input commands and set-up information to buffer manager50to enable the transfer of data from Soc processor34to imperfect memory device40. Data is commonly transferred between devices in the form of blocks, wherein one block data block comprises multiple bytes of data. Thus, the set-up information includes information such as clocking information, the number of blocks to be transferred and their associated logical block addresses, and any necessary DMA (direct memory access) signaling if processor34is DMA capable. The input commands and set-up information are stored in the plurality of set-up registers60and accessed by the hardware-implemented logic of buffer manager50. Set-up registers60also include information regarding buffer memory52such as available space within buffer memory56and where to begin the transfer of data. In one embodiment, buffer manager50further utilizes control path64to communicate interrupts to SoC processor34to notify SoC processor34of things such as the completion of a data transfer or whether a data error has been detected.

In one embodiment, buffer manager50includes a memory mapping block86to translate the logical block addresses utilized by SoC processor34to physical block addresses utilized by imperfect memory device40. Generally, imperfect memory devices, such as imperfect memory device40, include manufacturer provided memory mapping data indicating the imperfect memory locations or other memory locations that should not be over-written. In one embodiment, this memory mapping data is uploaded at system boot-up from a plurality of reserved storage areas on imperfect memory device40and stored in set-up registers60. The memory mapping data is then utilized by memory mapping block86to translate logical block addresses to physical block addresses, and vice-versa. In one embodiment, the memory mapping data is uploaded at boot-up from imperfect memory device40and stored in a memory within SoC processor34rather than in set-up registers60of buffer manager50. SoC processor34then utilizes the memory mapping data to translate between logical and physical block addresses in lieu of memory mapping block86.

Buffer memory52is a data buffer having a plurality of bit positions. Many devices, such as CompactFlash memory cards and hard disc drives, transfer data in the form of blocks wherein each block comprises 512 bytes of data. Thus, in one embodiment, the number of bit positions in buffer memory52comprises a multiple of 512 bytes thereby allowing buffer memory52to concurrently store multiple data blocks. In one embodiment, buffer memory52is configured to function as a circular buffer wherein a first block of data can be transferred into buffer memory52while a second block of data is simultaneously being transferred out of buffer memory52. As an illustrative example, if buffer memory52has five data block positions (2,560 bytes), a first data block can be transferred out of block position1while a second data block can be transferred into, for instance, block position5. In one embodiment, buffer memory52comprises a plurality of data block positions.

Processor translator54is coupled to SoC processor34via SoC processor data bus66and to buffer memory52via a first buffer data bus68, and comprises hardware implemented translation logic configured to synchronize the operation of processor data bus66and first buffer data bus68. Processor translator54compensates for those scenarios where the processor data bus operates at a different rate, usually higher, than buffer memory52and/or where processor data bus66has a different bus width than first buffer data bus68. As an illustrative example, SoC processor may be an ARM (Advanced RISC Machines, Ltd) core having an AHB (Advanced High-Performance) bus operating at 50 MHz and having width of 32-bits while first buffer data bus68may operate at 100 MHz and have a bus width of 16-bits. In one embodiment, processor translator54includes a buffer, or buffers, in the translation logic to temporarily store data received via a higher speed and/or greater width processor data bus for later transfer buffer memory52, thereby freeing processor data bus66for subsequent operations. Processor translator54also includes translation logic to coordinate the transfer data blocks to the appropriate data block position within buffer memory52.

Memory translator54is coupled to buffer memory56via a second buffer data bus70and to memory interface58via a first memory bus72and functions in a fashion similar to that of processor translator54, except that memory translator56comprises hardware implemented translation logic configured to synchronize the operation of second buffer data bus70and first memory bus72. Memory translator56compensates for those scenarios where buffer data bus70and first memory bus72operate at different rates and/or have different bit widths.

Memory interface58is coupled to memory translator56via first memory bus72and to imperfect memory device40via a second memory bus74, and is coupled to buffer manager50via a control path80. Memory interface comprises a hardware implemented addressing logic block82and a hardware implemented error correction code (ECC) logic block84. When receiving a data block to be written to imperfect memory device40via first memory bus72, ECC logic84generates an ECC comprising a plurality of bits for the data block that is a function of the data block. The ECC is then appended to the data block prior to writing the data block to imperfect memory device40.

When reading a data block read from imperfect memory device40, ECC logic84generates an expected ECC from the data block read from imperfect memory device40and compares the expected ECC to the ECC read from imperfect memory device40to determine whether the data block is in error. ECC logic84is configured to correct certain types of data errors and configured to provide an error indication to one of the plurality of set-up registers in buffer manager50via control path80if the data block contains an error of a type that is not correctable by ECC logic84.

Addressing logic82receives the physical block addresses associated with data blocks to be read from or written to imperfect memory device from buffer manager50via control path80and generates the necessary control and address signals to read the data block from or write the data block to imperfect memory device40. Both the address/control signals and data block are transmitted to imperfect memory device40via second memory bus74.

In conclusion, by integrating memory controller36onto SoC32, SoC processor34is able to read/write data directly to imperfect memory device40located within mobile electronic device30without the need for a separate memory controller chip or costly physical electrical interconnections (i.e., male-female pin connectors).