Patent Publication Number: US-11023388-B2

Title: Data path protection parity determination for data patterns in storage devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 62/734,654, filed Sep. 21, 2018, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the present disclosure relate to devices and methods for calculating data path protection (DPP) parity for defined data. 
     2. Description of the Related Art 
     The computer environment paradigm has shifted to ubiquitous computing systems that can be used anytime and anywhere. As a result, the use of portable electronic devices such as mobile phones, digital cameras, and notebook computers has rapidly increased. These portable electronic devices generally use a memory system having memory device(s), that is, data storage device(s). The data storage device is used as a main memory device or an auxiliary memory device of the portable electronic devices. 
     Data storage devices using memory devices provide excellent stability, durability, high information access speed, and low power consumption, since they have no moving parts. Examples of data storage devices having such advantages include universal serial bus (USB) memory devices, memory cards having various interfaces, and solid state drives (SSD). 
     The SSD may include flash memory components and a controller, which includes electronics that bridge the flash memory components to the SSD input/output (I/O) interfaces. The SSD controller may include an embedded microprocessor that executes functional components such as firmware. The SSD functional components are typically device specific, and in most cases, can be updated. 
     The two main types of flash memories are named after the NAND and NOR logic gates. The individual flash memory cells exhibit is internal characteristics similar to those of their corresponding gates. The NAND-type flash memory may be written to and read from in blocks (or pages) which are generally much smaller than the entire memory space. The NOR-type flash memory allows a single machine word (byte) to be written to an erased location or read independently. The NAND-type flash memory operates primarily in memory cards, USB flash drives, SSDs, and similar products, for general storage and transfer of data. 
     A flash-based storage device typically includes one or more flash chips, a microprocessor, volatile random access memory (RAM), which may be embedded or provided externally, and firmware that runs on the microprocessor. One function of a flash-based storage device is to provide a standard block interface for the flash chip(s) in the device to communicate with a host. The firmware uses RAM resources not only as storage for its internal data but also as a temporary storage for data received from a host during processing of a host read/write operation. DPP mechanisms are employed to protect host data from corruption in RAM. 
     In this context, embodiments of the present invention arise. 
     SUMMARY 
     Embodiments of the present invention are directed to faster more efficient techniques for calculating data path protection (DPP) parity. 
     Accordingly, an aspect of present invention includes a method for operating a memory controller to calculate data path protection (DPP) parity. Such method generally comprises receiving a first segment of host data; calculating a first parity of the first segment and an associated first logical block address (LBA); receiving a second segment of host data; and performing a logical operation on the first parity and a basic parity array to calculate a second parity of the second segment and its associated second LBA, the basic parity array being known to the memory controller based in part on the first and second segments. 
     Another aspect of the present invention is directed to a memory controller that comprises a processor configured to run firmware; a DPP engine in communication with the firmware; and a host interface configured to receive host data of a defined type, the host data comprised of multiple segments including a first segment and second segment. The DPP engine calculates a first parity of the first segment and an associated first LBA, whereas the firmware calculates a second parity of the second segment and an associated second LBA based on properties of the defined type of host data, which properties are known to the firmware after the first parity is calculated. 
     In another aspect of the present invention, a method for operating a memory controller to calculate DPP parity. The method comprises processing specific host data; determining whether DPP parity has been calculated for all LBAs of the specific host data; obtaining a next LBA for which DPP parity has not been calculated; calling a DPP engine of the memory controller to calculate the DPP parity for the next LBA and its associated piece of the specific host data, when the next LBA is the first LBA; executing firmware running on a processor of the memory controller to calculate the DPP parity for the next LBA and its associated piece of the specific host data, when the next LBA is not the first LBA. To calculate the DPP parity for the next LBA and its associated piece of specific host data, the firmware calculates the exclusive OR (XOR) difference between the next LBA and the immediately previously processed LBA. 
     Additional aspects of the present invention will become apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a memory system in accordance with an embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating a memory system in accordance with an embodiment of the present invention. 
         FIG. 3  is a circuit diagram illustrating a memory block of a memory device of a memory system in accordance with an embodiment of the present invention. 
         FIG. 4  is a logical diagram illustrating a flash-based storage device in accordance with an embodiment of the present invention. 
         FIG. 5  is a flow chart illustrating DPP parity calculation during is processing of a write the same command (WSC) in accordance with an embodiment of the present invention. 
         FIG. 6  is a flow chart illustrating processes of calculating DPP parity in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments are described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and thus should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough and complete and fully conveys the scope of the present invention to those skilled in the art. Moreover, reference herein to “an embodiment,” “another embodiment,” or the like is not necessarily to only one embodiment, and different references to any such phrase are not necessarily to the same embodiment(s). Throughout the disclosure, like reference numerals refer to like parts in the figures and embodiments of the present invention. 
     The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor suitable for executing instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being suitable for performing a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ or the like refers to one or more devices, circuits, and/or processing cores suitable for processing data, such as computer program instructions. 
     A detailed description of embodiments of the invention is provided below along with accompanying figures that illustrate aspects of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims. The invention encompasses numerous alternatives, modifications and equivalents within the scope of the claims. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example; the invention may be practiced according to the claims without some or all of these specific details. For clarity, technical material that is known in technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured. 
       FIG. 1  is a block diagram schematically illustrating a memory system in accordance with an embodiment of the present invention. 
     Referring  FIG. 1 , the memory system  10  may include a memory controller  100  and a semiconductor memory device  200 , which may represent more than one such device. The semiconductor memory device(s)  200  are preferably flash memory device(s), particularly of the NAND-type. 
     The memory controller  100  may control overall operations of the semiconductor memory device  200 . For simplicity, the memory controller  100  and semiconductor memory device  200  may sometimes be referred to below simply as controller  100  and memory device  200 , respectively. 
     The semiconductor memory device  200  may perform one or more erase, program, and read operations under the control of the memory controller  100 . The semiconductor memory device  200  may receive a command CMD, an address ADDR and data DATA through input/output (I/O) lines. The semiconductor memory device  200  may receive power PWR through a powerline and a control signal CTRL through a control line. The control signal CTRL may include a command latch enable (CLE) signal, an address latch enable (ALE) signal, a chip enable (CE) signal, a write enable (WE) signal, a read enable (RE) signal, and the like. 
     The memory controller  100  and the semiconductor memory device  200  may be integrated in a single semiconductor device such as a solid state drive (SSD). The SSD may include a storage device for storing data therein. When the semiconductor memory system  10  is used in an SSD, operation speed of a host (not shown) coupled to the memory system  10  may remarkably improve. 
     The memory controller  100  and the semiconductor memory device  200  may be integrated in a single semiconductor device such as a memory card. For example, the memory controller  100  and the semiconductor memory device  200  may be so integrated to configure a PC card of personal computer memory card international association (PCMCIA), a compact flash (CF) card, a smart media (SM) card, a memory stick, a multimedia card (MMC), a reduced-size multimedia card (RS-MMC), a micro-size version of MMC (MMCmicro), a secure digital (SD) card, a mini secure digital (miniSD) card, a micro secure digital (microSD) card, a secure digital high capacity (SDHC), and/or a universal flash storage (UFS). 
     In another embodiment, the memory system  10  may be provided as one of various components in an electronic device such as a computer, an ultra-mobile PC (UMPC), a workstation, a net-book computer, a personal digital assistant (PDA), a portable computer, a web tablet PC, a wireless phone, a mobile phone, a smart phone, an e-book reader, a portable multimedia player (PMP), a portable game device, a navigation device, a black box, a digital camera, a digital multimedia broadcasting (DMB) player, a 3-dimensional television, a smart television, a digital audio recorder, a digital audio player, a digital picture recorder, a digital picture player, a digital video recorder, a digital video player, a storage device of a data center, a device capable of receiving and transmitting information in a wireless environment, a radio-frequency identification (RFID) device, as well as one of various electronic devices of a home network, one of various electronic devices of a computer network, one of electronic devices of a telematics network, or one of various components of a computing system. 
       FIG. 2  is a detailed block diagram illustrating a memory system in accordance with an embodiment of the present invention. For example, the memory system of  FIG. 2  may depict the memory system  10  shown in  FIG. 1 . 
     Referring to  FIG. 2 , the memory system  10  may include a memory controller  100  and a semiconductor memory device  200 . The memory system  10  may operate in response to a request from a host device, and in particular, store data to be accessed by the host device. 
     The host device may be implemented with any of various kinds of electronic devices. In some embodiments, the host device may include an electronic device such as a desktop computer, a workstation, a three-dimensional (3D) television, a smart television, a digital audio recorder, a digital audio player, a digital picture recorder, a digital picture player, and/or a digital video recorder and a digital video player. In some embodiments, the host device may include a portable electronic device such as a mobile phone, a smart phone, an e-book, an MP3 player, a portable multimedia player (PMP), and/or a portable game player. 
     The memory device  200  may store data to be accessed by the host device. 
     The memory device  200  may be implemented with a volatile memory device such as a dynamic random access memory (DRAM) and/or a static random access memory (SRAM) or a non-volatile memory device such as a read only memory (ROM), a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a ferroelectric random access memory (FRAM), a phase change RAM (PRAM), a magnetoresistive RAM (MRAM), and/or a resistive RAM (RRAM). 
     The controller  100  may control storage of data in the memory device  200 . For example, the controller  100  may control the memory device  200  in response to a request from the host device. The controller  100  may provide data read from the memory device  200  to the host device, and may store data provided from the host device into the memory device  200 . 
     The controller  100  may include a storage  110 , a control component  120 , which may be implemented as a processor such as a central processing unit (CPU), an error correction code (ECC) component  130 , a host interface (I/F)  140  and a memory interface (I/F)  150 , which are coupled through a bus  160 . 
     The storage  110  may serve as a working memory of the memory system  10  and the controller  100 , and store data for driving the memory system  10  and the controller  100 . When the controller  100  controls operations of the memory device  200 , the storage  110  may store data used by the controller  100  and the memory device  200  for such operations as read, write, program and erase operations. 
     The storage  110  may be implemented with a volatile memory such as a static random access memory (SRAM) or a dynamic random access memory (DRAM). As described above, the storage  110  may store data used by the host device in the memory device  200  for the read and write operations. To store the data, the storage  110  may include a program memory, a data memory, a write buffer, a read buffer, a map buffer, and the like. 
     The control component  120  may control general operations of the memory system  10 , and a write operation or a read operation for the memory device  200 , in response to a write request or a read request from the host device. The control component  120  may drive firmware, referred to as a flash translation layer (FTL)  125 , to control general operations of the memory system  10 . For example, the FTL  125  may perform operations such as logical-to-physical (L2P) mapping, wear leveling, garbage collection (GC), and/or bad block handling. The FTL  125  may be imlemented, as firmware, in the controller  100 , and more specifically, in the control component  120 . The L2P mapping is known as logical block addressing. 
     The ECC component  130  may detect and correct errors in the data read from the memory device  200  during the read operation. The ECC component  130  may not correct error bits when the number of the error bits is greater than or equal to a threshold number of correctable error bits, and instead may output an error correction fail signal indicating failure in correcting the error bits. 
     The ECC component  130  may perform an error correction operation based on a coded modulation, such as a low-density parity-check (LDPC) code, a Bose-Chaudhuri-Hocquenghem (BCH) code, a turbo code, a turbo product code (TPC), a Reed-Solomon (RS) code, a convolution code, a recursive systematic code (RSC), a trellis-coded modulation (TCM), or a block coded modulation (BCM). The ECC component  130  may include any and all circuits, systems or devices for suitable error correction operation. 
     The host interface  140  may communicate with the host device through one or more of various interface protocols, such as a universal serial bus (USB), a multi-media card (MMC), peripheral component interconnect express (PCI-e or PCIe), a small computer system interface (SCSI), a serial-attached SCSI (SAS), a serial advanced technology attachment (SATA), a parallel advanced technology attachment (PATA), non-volatile memory express (NVMe), an enhanced small disk interface (ESDI), and integrated drive electronics (IDE). 
     The memory interface  150  may provide an interface between the controller  100  and the memory device  200  to allow the controller  100  to control the memory device  200  in response to a request from the host device. The memory interface  150  may generate control signals for the memory device  200  and process data under the control of the control component (or CPU)  120 . When the memory device  200  is a flash memory such as a NAND flash memory, the memory interface  150  may generate control signals for the memory and process data under the control of the CPU  120 . 
     The memory device  200  may include a memory cell array  210 , a control circuit  220 , a voltage generation circuit  230 , a row decoder  240 , a page buffer (array)  250 , which may be in the form of an array of page buffers, a column decoder  260 , and an input/output circuit  270 . The memory cell array  210  may include a plurality of memory blocks  211  which may store data. Subsets of the memory blocks may be grouped into respective super blocks for certain operations. 
     The voltage generation circuit  230 , the row decoder  240 , the page buffer (array)  250 , the column decoder  260  and the input/output is circuit  270  may form a peripheral circuit for the memory cell array  210 . The peripheral circuit may perform a program, read, or erase operation of the memory cell array  210 . The control circuit  220  may control the peripheral circuit. 
     The voltage generation circuit  230  may generate operation voltages of various levels. For example, in an erase operation, the voltage generation circuit  230  may generate operation voltages of various levels such as an erase voltage and a pass voltage. 
     The row decoder  240  may be in electrical communication with the voltage generation circuit  230 , and the plurality of memory blocks  211 . The row decoder  240  may select at least one memory block among the plurality of memory blocks  211  in response to a row address RADD generated by the control circuit  220 , and transmit operation voltages supplied from the voltage generation circuit  230  to the selected memory blocks. 
     The page buffer (array)  250  may be in electrical communication with the memory cell array  210  through bit lines BL (shown in  FIG. 3 ). The page buffer (array)  250  may pre-charge the bit lines BL with a positive voltage, transmit data to, and receive data from, a selected memory block in program and read operations, or temporarily store transmitted data, in response to page buffer control signal(s) generated by the control circuit  220 . 
     The column decoder  260  may transmit data to, and receive data from, the page buffer (array)  250 , and may also exchange data with the input/output circuit  270 . 
     The input/output circuit  270  may transmit to the control circuit  220  a command and an address, received from an external device (e.g., the memory controller  100 ), transmit data from the external device to the column decoder  260 , or output data from the column decoder  260  to the external device, through the input/output circuit  270 . 
     The control circuit  220  may control the peripheral circuit in response to the command and the address. 
       FIG. 3  is a circuit diagram illustrating a memory block of a semiconductor memory device in accordance with an embodiment of the present invention. For example, the memory block of  FIG. 3  may be any of the memory blocks  211  of the memory cell array  200  shown in  FIG. 2 . 
     Referring to  FIG. 3 , the exemplary memory block  211  may include a plurality of word lines WL 0  to WLn- 1 , a drain select line DSL and a source select line SSL coupled to the row decoder  240 . These lines may be arranged in parallel with the plurality of word lines between the DSL and SSL. 
     The exemplary memory block  211  may further include a plurality of cell strings  221  respectively coupled to bit lines BL 0  to BLm- 1 . The cell string of each column may include one or more drain selection transistors DST and one or more source selection transistors SST. In the illustrated embodiment, each cell string has one DST and one SST. In a cell string, a plurality of memory cells or memory cell transistors MC 0  to MCn- 1  may be serially coupled between the selection transistors DST and SST. Each of the memory cells may be formed as a multi-level cell (MLC) storing data information of multiple bits. 
     The source of the SST in each cell string may be coupled to a common source line CSL, and the drain of each DST may be coupled to the corresponding bit line. Gates of the SSTs in the cell strings may be coupled to the SSL, and gates of the DSTs in the cell strings may be coupled to the DSL. Gates of the memory cells across the cell strings may be coupled to respective word lines. That is, the gates of memory cells MC 0  are coupled to corresponding word line WL 0 , the gates of memory cells MC 1  are coupled to corresponding word line WL 1 , etc. The group of memory cells coupled to a particular word line may be referred to as a physical page. Therefore, the number of physical pages in the memory block  211  may correspond to the number of word lines. 
     As previously noted, the page buffer (array)  250  may be in the form of a page buffer array including a plurality of page buffers  251  that are coupled to the bit lines BL 0  to BLm- 1 . The page buffers  251  may operate in response to page buffer control signals. For example, the page buffers  251  my temporarily store data received through the bit lines BL 0  to BLm- 1  or sense voltages or currents of the bit lines during a read or verify operation. 
     In some embodiments, the memory blocks  211  may include a NAND-type flash memory cell. However, the memory blocks  211  are not limited to such cell type, but may include NOR-type flash memory cell(s). Memory cell array  210  may be implemented as a hybrid flash memory in which two or more types of memory cells are combined, or one-NAND flash memory in which a controller is embedded inside a memory chip. 
     As previously noted, the memory controller  100  and the semiconductor memory device  200  may be integrated into a single device such as an SSD or other flash-based storage device. Referring to  FIG. 4 , an exemplary flash-based storage device  40  is illustrated. Flash-based device  40 , which may be another embodiment of memory system  10 , is shown here with a somewhat different layout to highlight features and aspects of the present invention. The flash-based device  40  may include a controller  41  (Control HW) and a storage  42 , which generally correspond to the memory controller  100  and memory device  200 , respectively, of  FIG. 2 . The storage  42  may include multiple flash chips collectively identified by  42   a.    
     The controller  41  may include a system-on-chip (SoC)  43 , on or in which are embedded various components described below. The controller  41  may further include a random access memory (RAM)  44 , such as that included in storage  110 . 
     The SoC  43  includes a processor, which may be an embedded microprocessor (pP)  45  and a DPP engine  46  in communication with the microprocessor  45 . Firmware  45   a  runs on the microprocessor  45 , which is in communication with the RAM  44 . The SoC  43  further includes host interface logic  47  in communication with the microprocessor  45  and also in communication with a host  50 . Flash interface logic  48  on the SoC  43  provides communication between the SoC  43  and the storage  42 . 
     As previously noted, in flash-based storage devices, data path protection (DPP) mechanisms are employed to protect host data from corruption in RAM. Such mechanisms involve calculating a check value from raw host data for further error detection and correction. Usually, a linear code, e.g., cyclic redundancy check (CRC), is used for DPP parity calculation. For better performance, a hardware (HW) engine is used for DPP parity check and calculation. 
     Embodiments of the present invention provide techniques for more efficiently calculating DPP parity for certain defined host data. The inventive techniques use properties of linear codes that allow calculating DPP parity faster than a HW engine. 
     A linear code, defined as G, has the following property:
 
 G ( a⊕b )= G ( a )⊕ G ( b )
 
     Assume that the FW  45   a  receives a piece of raw host data a and calls the DPP engine  46  to calculate DPP parity G(a). Then, the FW  45   a  receives another piece of raw host data b. At that time, though, certain information is available to the FW  45   a . That is, the FW  45   a  knows certain information denoted as Δ from the following relationship: b=a⊕Δ, and also knows G(Δ). In this case, the FW  45   a  can easily calculate DPP parity for b, without calling the DPP engine  46 , using the following property of the above linear code:
 
 G ( b )= G ( a )⊕ G (Δ)
 
     DPP parity is calculated from an LBA value and the host data which relates to the LBA. However, there are several cases when the host data is the same for some range of LBAs, e.g., Write Zeros Command (WZC), Write the Same Command (WSC), etc. Without any optimization, the FW  45   a  has to call the DPP engine  46  to calculate DPP parity for each LBA and related host data. This significantly reduces performance especially when the range of LBAs is large. Also, during processing of such commands, the DPP engine  46  is not available for other tasks, such as parity verification of data loaded from NAND. 
     To show how to avoid performance degradation during processing of WSC for some range of LBAs, it is assumed that the FW  45   a  receives a WSC for LBA  0  and LBA  1  (where the size of an LBA is 4 Bytes). The following array of pre-calculated DPP parties should be available for the FW  45   a , denoted as BasicParities, and defined as follows: (1) the array has 32 elements; and (2) an i th  element of the array is G(x i ), where all bits of x i  equal zero, except the i th  bit. 
     With this in mind, define LBA  0  and host data as a, and LBA  1  and host data as b. For LBA  0  and the host data, the FW  45   a  calls the DPP engine  46  to calculate parity, defined as G(a). Taking into account that the host data is the same for both LBAs and that LBA  0  and LBA  1  are different only in one bit at position  0 , DPP parity can be calculated by the FW  45   a  itself from G(a):
 
 G ( b )= G ( a )⊕BasicParities[0]
 
       FIG. 5  is a flow chart  500  illustrating DPP parity calculation during processing of a WSC by the FW  45   a , in accordance with an embodiment of the present invention. 
     In step  501  DPP parity calculation is started during the processing of a WSC. At step  502 , it is determined whether or not DPP parity has been calculated for all LBAs of the WSC host data. This step is somewhat trivial at the start of the processing, but becomes more significant as the processing iterations increase. 
     When there is at least one LBA for which DPP parity has not been calculated (No at step  502 ), it is then determined at step  503  whether the current LBA (in a sequence of LBAs) is the first LBA, which is treated differently than the second and subsequent LBAs. If the next LBA is the first LBA (Yes at step  503 ), processing moves to step  504 , where the DPP engine  46  is called to calculate the DPP parity for the first LBA and associated host data. Following that calculation, that DPP parity is stored, e.g., in RAM  44 , at step  505 . 
     After storing the DPP parity for the first LBA, the process returns to step  502 . If there is a second (or another) LBA for which a DPP parity is to be calculated, flow passes through the “No” branches of steps  502  and  503  to step  506 . 
     At step  506 , the firmware  45   a  is used to make calculations. More specifically, at step  506 , the firmware  45   a  calculates the XOR difference between the current LBA and the immediately previous LBA that has already been processed. In step  507 , processing variable, i, is set to 0. 
     At step  508 , it is determined whether or not the number of bits in the current LBA is equal to i. Essentially, this step acts as counter for processing bits in the current LBA. Initially, the determination at step  508  is “No” and at each pass it continues to be “No”, the flow moves to step  509 , where it is determined whether or not the i th  bit of the XOR difference is 1. If not, i is incremented at step  510 , after which the determination at step  508  is made again. This loop of steps  508 ,  509  and  510  continues until, at step  509 , it is determined that the i th  bit of the XOR difference is 1. 
     When this happens (Yes at step  509 ), a further calculation is performed at step  511 . An XOR operation is performed on previously calculated DPP parity and the i th  element of the BasicParities. After that, i is incremented and the process returns to step  508 . Processing continues within the loops defined by steps  508 - 511 , until is finally determined that i is equal to the number of bits in the current LBA. When that happens (Yes at step  508 ), the DPP parity calculations made at step  511  are stored at step  505 . Such calculations may be stored in RAM  44 . 
     After each DPP parity storage occurrence (step  505 ), the process returns to step  502 , where it is once again considered whether DPP parities have been calculated for all LBAs. If not, the processing continues as previously described. If so (Yes at step  502 ), the DPP parity calculation process ends (step  512 ). 
       FIG. 6  is a flow chart  600  describing steps in processes of DPP parity calculation, in accordance with embodiments of the present invention. The steps shown in flow chart  600  are exemplary. Those skilled in the art will understand that additional and/or alternative steps may be performed, or that the order of steps may be changed, to effectuate aspects of the present invention without departing from the is inventive concepts disclosed herein. 
     At step  601 , a first segment of host data is received by the memory system, e.g., flash-based device  40 . At step  602 , a first DPP parity of the first segment and its associated first LBA is calculated. For certain host data, e.g., WSC, the DPP engine  46  is called to calculate the first DPP parity. After being calculated, the first DPP parity is stored in memory, e.g., RAM  44 , at step  603 . 
     At step  604 , a second segment of host data is received by flash-based device  40 . For this segment and all subsequent segments, at step  605 , the firmware  45   a  is executed to calculate a second DPP parity by performing a logical operation, e.g., XOR operation, on the immediately the first DPP parity and a basic parity array. More generally, the firmware  45   a  calculates the DPP parity for each of the second and subsequent segments of host data by performing a logical operation, e.g., XOR operation, on the immediately previously calculated DPP parity and the basic parity array. 
     At step  606 , the second parity is stored in memory. More generally, each of the second and subsequent parities is stored in memory after being calculated. 
     As the foregoing demonstrates, embodiments of the present invention provide techniques to more efficiently calculate DPP parity. Firmware is advantageously used for such calculation with limited or no calls to the DPP engine, depending on the type of host data. 
     Although the foregoing embodiments have been illustrated and described in some detail for purposes of clarity and understanding, the present invention is not limited to the details provided. There are many alternative ways of implementing the invention, as one skilled in the art will appreciate in light of the foregoing disclosure. The disclosed embodiments are thus illustrative, not restrictive.