Technical Note. Refresh Features for Micron e.mmc Automotive 5.0 Devices. Introduction. TN-FC-54: Refresh Features for e.mmc Automotive 5.

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1 Technical te TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Introduction Refresh Features for Micron e.mmc Automotive 5.0 Devices Introduction This technical note describes additional data refresh features available in Micron e.mmc automotive 5.0 devices built with Micron firmware. These features enable further management of the REFRESH operation and are based on the JEDEC applicationspecific command CMD56, available in JESD84-B50. In addition, possible algorithms of manual scan and refresh are reported. 1 Products and specifications discussed herein are subject to change by Micron without notice.

2 REFRESH Operation Table 1: Manual BKOPS Data retention is the length of time that the NAND storage media inside an e.mmc device retains data, with biased or unbiased conditions. Limited data retention makes memory device scanning and refresh essential. An inverse relationship exists between data retention and the PROGRAM/ERASE (P/E) cycles and temperature that affect a device over time. When either or both P/E cycles and temperature increase, data retention decreases, making a REFRESH operation necessary. A REFRESH operation is executed when a device scan shows that the number of flip bits are greater than the ECC threshold for the given NAND technology. ECC is able to correct the errors; the corrected data is then copied into a new destination block. A RE- FRESH operation writes data into a new memory location. The e.mmc device firmware manages REFRESH on virtual blocks, which are a software grouping of physical blocks across the NAND die to take advantage of parallel WRITE operations. Virtual block size varies by device size, and the firmware is able to build a queue of the virtual blocks to be refreshed. Manual refresh is recommended when the e.mmc device provides information as shown in the table below. Manual refresh is managed through CMD6. Function MANUAL BKOPS Information Stimulate refresh via manual BKOPS TN-FC-54: Refresh Features for e.mmc Automotive 5.0 REFRESH Operation EXCEPTION_EVENTS_STATUS[54], UR- GENT_BKOPS bit = 1 BKOPS_STATUS [246] = 3 Host is informed about the refresh condition; see JEDEC specification. 2

3 Additional e.mmc Automotive 5.0 Refresh Features The additional e.mmc automotive 5.0 refresh features fully control refresh management, even of data that is seldom read or not involved in the REFRESH operation described in the previous section. These features act on virtual blocks in an e.mmc device and require the adoption of the POWER OFF NOTIFICATION operation, as described in the JEDEC specification JESD84-B50. The additional e.mmc automotive 5.0 refresh features are based on the JEDEC application-specific command CMD56. Table 2: Additional e.mmc Automotive 5.0 Refresh Features TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features Refresh Feature User initiated refresh standard mode User initiated refresh blind mode Automatic initiated refresh Refreshes a range of logical block addresses (LBAs) when the number of bit failures reaches a set threshold. Refreshes the entire e.mmc device, even without meeting a bit failure threshold. Automatically refreshes a range of LBAs when a bit failure reaches a set threshold; requires preset algorithm. User Initiated Refresh Standard Mode User initiated refresh (UIR) standard mode refreshes virtual blocks belonging to an indicated range of LBAs if they show bit failures over a defined threshold. This feature is useful after the reflow of pre-programmed devices. The CMD56 command contains these UIR standard mode parameters: Table 3: CMD56 UIR Standard Mode Parameters Parameter LBA start LBA stop Refresh threshold Starts the REFRESH operation from this logical address Stops the REFRESH operation at this logical address The bit error threshold for the REFRESH operation Table 4: UIR Standard Mode Argument Bit Argument The e.mmc firmware reads the LBAs between start and stop, and if the number of bit errors is greater than or equal to the refresh threshold, the firmware refreshes the virtual blocks where the LBAs are placed. UIR standard mode is configured by CMD56 into the write mode similar to a SINGLE- BLOCK WRITE command with this argument: [0] 0 (Write Mode) [7:1] (Index = 0x52) [15:8] "Don t Care" (Argument #1) [16:23] "Don t Care" (Argument #2) 3

4 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features Table 4: UIR Standard Mode Argument (Continued) Bit Argument [31:24] All 0 (Reserved) After CMD56, the read scan information must be written to the device in form of one sector: Table 5: UIR Standard Mode Sector Byte [0 3] [4 7] Action Refresh Start Logical Address (Byte[3] is low byte) (LBA_start) Refresh End Logical Address (Byte[7] is low byte) (LBA_stop) [8] Refresh ECC threshold (Refresh threshold) The allowed values are 10, 20, 30 otherwise an error is reported (bit 19 is set in card status) Issue CMD13 (SEND_STATUS) to obtain the result of the function. After CMD56, the device goes busy for the time necessary for the refresh. This time is variable and depends on the status of the device. The refresh can be interrupted by high priority interrupt (HPI). A further UIR command on the same LBA range does not resume the previous interrupt operation. To ensure the entire selected LBA range is refreshed, the host must re-issue the CMD56 in the same range. The virtual blocks, for which HPI interrupts the refresh, is concluded as per standard REFRESH DEFRAG operation during next WRITE/READ operations. 4

5 Figure 1: User Initiated Refresh Standard Mode TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features Start CMD56: GEN_CMD [0] = 0 (Write), [7:1] = (Index) Send 1 sector data to the card 1 CMD13: SEND_STATUS Error? <ERROR > 2 Function passed End tes: 1. Byte[3:0]: Refresh Start Address Byte[7:4]: Refresh End Address Byte8: Refresh ECC Threshold. 2. LBA out of addressable range: Bit19 is set value for refresh threshold is not allowed: Bit19 is set. 5

6 User Initiated Refresh Blind Mode User initiated refresh (UIR) blind mode refreshes the entire e.mmc device, regardless of bit failures. By using this feature, the host takes advantage of idle time to clean the e.mmc device. The refresh of the entire memory is performed during the busy state of CMD56 and can be interrupted by HPI. If interrupted, the next blind refresh command resumes the procedure from the last checkpoint. Progress can be monitored by reading EXT_CSD: Counter = EXT_CSD [69-70] incremented at the end of an entire memory refresh. Byte [70] is HIGH and [69] is LOW. Refresh status, percentage = {EXT_CSD[81]<<8 EXT_CSD[80]} For example: Table 6: UIR Blind Mode Argument Bit Argument EXT_CSD[80] = 0x29 and EXT_CSD[81] = 0x09 Obtain the percentage by combining the registers (EXT_CSD[81]<<8 EXT_CSD[80]) = 0x0929 and converting from hexadecimal to decimal = It correspond to 23.54%. UIR blind mode is applied to all user partitions on the e.mmc device, including boot and RPMB blocks and buffer area. The system area is refreshed as consequence of the user area refresh. The firmware refreshes all the virtual blocks with valid data inside, skipping the invalid. During the refresh, garbage collection is also executed. The interrupted REFRESH operation is resumed during the next write/read access until the virtual block refresh completes (atomic operation of blind mode is based on one virtual block). If a next blind mode refresh is started before the completion of the atomic operation, the blind mode refresh resumes from the beginning of the interrupted virtual block. HPI during blind mode refresh shows the maximum latency as per EXT_CSD [198] OUT_OF_INTERRUPT_TIME. UIR blind mode is configured by CMD56 into the write mode similar to a SINGLE- BLOCK WRITE command with this argument: [0] 0 (Write Mode) [7:1] (Index = 0x52) [15:8] "Don t Care" (Argument #1) [16:23] "Don t Care" (Argument #2) [31:24] All 0 (Reserved) TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features The argument must be followed by one sector of all 0x00. Issue CMD13 (SEND_STATUS) to obtain the result of the function. 6

7 Figure 2: User Initiated Refresh Blind Mode TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features Start CMD56: GEN_CMD [0] = 0 (Write), [7:1] = (Index) Send 1 sector data to the card 1 CMD13: SEND_STATUS Error? <ERROR Management> Function passed End te: 1. Byte[11:5] = 0x00. 7

8 Automatic Initiated Refresh Table 7: AIR Parameters TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features Automatic initiated refresh (AIR) mode automatically scans and reads the entire user area, divided in sector ranges. Each virtual block (belonging to the range) where bit failures are present is booked for refresh. The presence of bit failures is notified by EXT_CSD [246] _BKOPS_STATUS = 0x3 and device status URGENT BKOPS = 1 until the refresh completes. The read scan of each range starts periodically based on the number of host READ commands. Contiguous ranges of virtual blocks are scanned sequentially. After the firmware has checked the entire area, it starts again from the beginning. The REFRESH operation is performed in the background during normal usage (busy) times. Enable AIR mode using the CMD56 command, which can also be used to set or change the parameters. Parameter X Y Number of READ commands after which the firmware starts the check for refresh. The value is stored in EXT_CSD [72-75] (72 is LOW). Quantity of LBAs to be checked each time. The value is stored in EXT_CSD [76-79] (76 is LOW). The enable/disable flag is stored in EXT_CSD[71]. AIR mode is configured by CMD56 into the write mode similar to a SINGLE-BLOCK WRITE command with this argument: Table 8: AIR Argument Bit Argument [0] 0 (Write Mode) [7:1] (Index = 0x54) [15:8] "Don t Care" (Argument #1) [16:23] "Don t Care" (Argument #2) [31:24] All 0 (Reserved) After CMD56, one sector (read scan information) must be written to the device: Table 9: AIR Sector Byte Action [0] Read scan enable (set 0x01) [1-4] Number of READ commands after which the firmware should start check for refresh ; (Byte[4] is LOW) [5-8] Number of LBA sectors (range size) to be checked each time (Byte[8] is LOW) Issue CMD13 (SEND_STATUS) to obtain the result of function. 8

9 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Additional e.mmc Automotive 5.0 Refresh Features Figure 3: Automatic Initiated Refresh Start CMD56: GEN_CMD [0] = 0 (Write), [7:1] = (Index) Send 1 sector data to the card 1 CMD13: SEND_STATUS (mandatory) Error? General error bit (Bit19) Function failed Function passed End te: 1. Byte0: Read Scan Enable Byte[4:1]: Number of read CMD after which the firmware starts check for refresh ; Byte4 is LOW Byte[8:5]: Range of LBAs to be checked each time; Byte8 is LOW. 9

10 Implementation Manual Scan and Refresh TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Implementation During production, e.mmc automotive devices that are pre-programmed and then soldered can be refreshed to restore eventual bit failures due to thermal stress using one of the User Initiated Refresh modes: UIR Standard Mode: Refreshes a range of LBAs when a bit failure reaches a set threshold. te: this mode takes a longer amount of time when a large range of LBAs and a low threshold are set. UIR Blind Mode: Refreshes the entire e.mmc device, even without meeting a bit failure threshold. During the application lifetime, it is safe to refresh data that is not often read using one of these options: UIR Blind Mode: Can be started periodically, and interrupted and resumed Automatic Initiated Refresh: Refreshes data if the number of bit failures is over the set threshold. In this case, the host must set the algorithm described in Automatic Initiated Refresh. t adopting the additional e.mmc refresh feature, the refresh can be directly managed by the host. This section describes different possible implementation of the manual scan and refresh algorithm to be tailored on the application-specific requirements. This algorithm includes common e.mmc operations: READ to the e.mmc user area (to scan blocks) Check of the card status and/or EXT_CSD (to verify that refresh is required) WRITE operations from the normal use (dummy on the user area) to trigger the refresh if needed The designed algorithm is executed periodically (cron script), considering as the refresh period the timeframe for the host to complete the user area scanning (for example, one year). The scanning is divided into several steps during this timeframe. Each step targets a range of LBAs and, consequently, affects all virtual blocks correlated to that LBA range. Consecutive steps target contiguous ranges of LBAs. The host has the burden to save and update addresses. The size of the scan range influences the evolution of the algorithm. The larger the LBA range, the larger the number of virtual blocks involved in the scan that eventually will require the refresh. Considering that the queue of blocks booked for refresh is limited, if refreshes are triggered, it is recommended to repeat the scan on the same range to assure that all eventual weak virtual blocks are refreshed. Table 10: Manual Scan and Refresh Variables Defined in the Host Software Variable Last_Addr Represents the last LBA checked by the host. Last_addr is initialized = 0 and varies up to SEC_COUNT (ECSD [215:212]). 10

11 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Implementation Table 10: Manual Scan and Refresh Variables Defined in the Host Software (Continued) Variable Refresh_Period Scan_range Timeframe for user area to complete scanning. This value must be based on customer requirements. The complete scan is divided into several scans during refresh_period. Range of LBA to be read in each scan step. This range must be submultiples of sec_count. Regular version of the algorithm works with a single range (Scan_range). In this example, the algorithm is executed periodically (cron script) and WRITE operations of the normal usage trigger the refresh until the BKOPS condition is cleared. A possible value of Scan_range is 128KB. 11

12 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Implementation Figure 4: Manual Scan and Refresh (Example 1) Read Last_Addr from file File exist? Create file Write to file Last_Addr = 0 CMD18 (addr = Last_Addr, chunk = Scan_range) READ_MULTIPLE_BLOCK CMD13 SEND_STATUS Device status EXCEPTION_EVENT (Bit6) set? CMD8 SEND_EXT_CSD Bkops status = 3? Write to File Last_Addr = Last_Addr + Scan_range Exit Last_Addr > SECT_COUNT? Write to File Last_Addr = 0 Exit 12

13 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Implementation An implementation of this algorithm is done with a bash script that is inside the emmcparm package. The script is in the directory "/usr/refresh" named "./read_scan_refre.sh" and accepts as input option the following: 1. Device file to be refreshed ex. /dev/mmcblk0 2. Refresh_Period in hours 3. Debug option "1" print read data to terminal Is also possible to run the script in background as daemon using setsid: sudo setsid./read_scan_refre.sh /dev/mmcblk1 1 >./log.log 2>&1 < /dev/null & In this case a log file named log.log is produced if no log file is needed change "./ log.log" with "/dev/null" In the example below, the scan proceeds with large ranges (2MB or larger). In case a refresh is triggered, the verification on the same range is split into smaller ranges (for example, 64KB). Dummy writes are used to perform the refresh until the URGENT BKOPS info is cleared. Table 11: Manual Scan and Refresh Variables Defined in the Host Software (Additional) Variable Last_Addr_Step Scan_big_range Scan_small_range Write_chunk, write_address Represents the last LBA checked by the host in case of verification of the last scanned area. Range of LBA to be read in each scan step. This range must be submultiples of sec_count. Range of LBA to be read in each small step in case of reverification of the last checked area. This range must be a submultiple of scan_big_range. Refresh is done by the e.mmc internal firmware in the background during a host WRITE operation. These variables are "Don't Care." 13

14 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Implementation Figure 5: Manual Scan and Refresh (Example 2) Start Refresh period elapsed Last_Addr = 0 CMD18 (Last_Addr, Last_Addr + Scan_big_range) CMD13 Check card status CMD25 (Write_address, Write_chunk) CMD13 Check card status Last_Addr_Step = Last_Addr CMD18 (Last_Addr_Step + Scan_small_range) Bit6 = 1 Bit6 = 1 Bit6 = 1 CMD8 Send_Ext_CSD CMD8 Send_Ext_CSD CMD8 Send_Ext_CSD Last_Addr > Sec_Count Bkops_ Status = 3 Bkops_ Status = 3 Bkops_ Status = 3 Last_Addr = Last_Addr + Scan_big_range Last_Addr_Step > Last_Addr + Scan_big_range CMD25 (Write_address, Write_chunk) Last_Addr_Step = Last_Addr_Step + Scan_small_range A simplified version of the algorithm works with a single range (scan_range). 14

15 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Implementation Figure 6: Manual Scan and Refresh (Example 3) Start Refresh period elapsed Last_Addr = 0 Last_Addr > Sec_Count CMD18 (Last_Addr, Last_Addr + Scan_big_range) CMD25 (Write_address, Write_chunk) CMD13 Check card status CMD13 Check card status Last_Addr = Last_Addr + Scan_big_range Bit6 = 1 Bit6 = 1 CMD8 Send_Ext_CSD CMD8 Send_Ext_CSD Bkops_ Status = 3 Bkops_ Status = 3 15

16 TN-FC-54: Refresh Features for e.mmc Automotive 5.0 Revision History Revision History Rev. C 03/18 Rev. B 03/17 Rev. A 08/16 Improved verbiage on the introduction, refresh operation and implementation paragraphs Added Scan_range row in table 11 Added figure 4 Updated value in Table 8, bit[7:1], from to Included Scan_range in the description of Table 10 Added paragraph to describe the implementation of Manual Scan and Refresh Implementation in emmcparm Initial release 8000 S. Federal Way, P.O. Box 6, Boise, ID , Tel: Sales inquiries: Micron and the Micron logo are trademarks of Micron Technology, Inc. All other trademarks are the property of their respective owners. This data sheet contains minimum and maximum limits specified over the power supply and temperature range set forth herein. Although considered final, these specifications are subject to change, as further product development and data characterization sometimes occur. 16