Ensuring NAND Flash and Data Integrity of Dashcam Memory Cards (Part 2)

PublishTime： 2022-09-02 Article Source：ATP ELECTRONICS

As mentioned in Part 1 Endurance, Latency, and Workload Considerations for Choosing Dashcam Memory Cards, many user behaviours may cause NAND storage failure, such as long-term recording, environmental conditions, or power supply instability. We present the three most frequent causes of data corruption, their fixes, and an enhanced analysis approach based on NAND technology and user behaviours:

Issue 1: NAND Flash Voltage Shifts

Flash may wear out as recording time increases and other factors such as high/low temperatures causing the dynamic voltage distribution. DVRs have largely embraced Memory Cards using 3D Triple-level-cell NAND in the meantime. While benefiting from the NAND Technology innovation's higher density at an affordable price, the smaller read window's difficulty for bits per cell results in read errors. (Refer to Figure 1)

Figure 1: bits/cell challenge of smaller read window creates read inaccuracies

ATP Solutions: Read Retry + Auto Read Calibration (ARC)

In order to recover from bit errors and read the proper information, it is necessary to optimize the reference voltage inside the read window. As a result, the effectiveness of the Read Retry and Auto-Read-Calibration (ARC) mechanisms is demonstrated below.

Figure 2: voltage distribution is dynamic

Figure 3: 3D NAND requires more calibration levels than planar NAND

ATP SD cards automatically activate Read Retry when the voltage distribution shifts. Read Retry is a scale of voltage calibration method to find a reference voltage for data reading. If the read still fails for bit errors beyond the ECC threshold and is unable to be judged correctly by the read retry scale, a subtle and more precise voltage adjustment, Auto Read Calibration (ARC), will be applied.

This feature can be likened to listening to a radio channel. For example, you want to listen to the channel 93.6kHz without noise. Read Retry allows you to set the knob to 93kHz. With Read Retry plus ARC, you can make a precise adjustment to 93.6kHz.

Figure 4: Read Retry plus ARC can make a precise adjustment

Issue 2: Read Disturbances

In the previous section, we mentioned that there are more and more interferences between neighbouring cells with the NAND evolution, which may cause lower margins for error handling. After long-term and massive read operations, electric charges in the cell may have an impact on the voltage threshold, and lead to read disturbances.

ATP Solution: Read Disturb Protector – Monitor both error bits and read counts

Read Disturb Protector aims to prevent read disturbance by monitoring both error bits and read counts in each read operation. Once the error bits reach the pre-set threshold¹, the ATP firmware (FW) will take action by moving data from the high-risk block to a healthy block and marking the original block. Depending on the risk level, we will determine to re-use the original block or mark it as a bad block.

¹ECC threshold may vary depending on FW & BOM configuration.

Issue 3: Sudden Power Loss

ATP Solutions: Back-up Mechanism and SPOR (Sudden Power Off Recovery)

3.1 Back-up firmware mechanism

Any unplanned power outage could result in vital data being lost or corrupted. The worst-case scenario is memory card malfunction if a power outage happens while updating system tables. System tables, including the FW/ISP code, FTL info table, and boot table, are contained in the NAND flash SLC mode blocks.

Although the SLC mode blocks are sturdy, backup tables are kept in a different system block to prevent the crash of the main system tables. As a result, the data on the SD card can be accessed from either the primary system tables or the backup system tables.

3.2 ATP Sudden Power-Off Recovery (SPOR)

The basic unit of a memory chip is a cell, and the cells are arranged in a row called a word line (WL). The lower page, upper page, and extra page are paired pages in the TLC architecture that share the same word line. Data corruption and data integrity issues may result from incomplete programming in the same WL (an open word line).

To save as much data as possible, ATP Sudden Power-Off Recovery (SPOR) firmware will fill dummy patterns in the remaining cells of the same WL so as to complete the WL programming (close word line).

Taking Figure 3 below as an example, ATP SPOR firmware mechanism completes the programming operation on page 36 by filling in paired pages 66 and 69 in the same WL with a dummy pattern. This can guarantee that the whole operation is completed and the data in page 36 is saved.

Figure 5: SPOR firmware fills in the remaining cells with a dummy pattern.

Advanced Card Analysis for SiP (System-In-Package) Memory Cards

Memory cards are IP67/IP57-certified and manufactured using System-in-Package (SiP) wafer/die process that integrates components within a single package, making it resistant to water/dust/shock. However, SiP protection also makes memory cards difficult to perform component analysis. ATP's solution is the Analysis Methodology for SiP Memory Cards, which features a uniquely designed substrate and debug tool that make this mission "possible."

Figure 6: ATP Analysis Methodology for System-In-Package Memory Cards

Why Dashcam Manufacturers Should Consider Bundling ATP High-endurance memory cards

For over 30 years, ATP has been a leading manufacturer with world-class hardware/firmware (HW/FW) capabilities. It uses leading-edge technologies to ensure its products' maximum reliability and extended endurance and can adjust to a variety of usages to fulfil customers' specific application requirements and conditions.

Customization and Joint Validation

ATP is capable of adjusting to a variety of usages to fulfil customers' specific application requirements and conditions. Its own-developed firmware and hardware design, together with supporting mass production infrastructure, are fully customizable to meet customers' criteria.

• Software joint integration (e.g., SD Life Monitor)

• Compatibility tests

• Function/performance enhancement

• Signal measurement

• Additional test (industry standard, Power Cycling Test)

Manufacturer's Warranty Policy

The new ATP S650/S750 Series SD/microSD cards are specifically purpose built for write-intensive applications such as dashcams, DVRs, and surveillance cameras; as such, there is no need to worry that the warranty will become void due to intense video recording use.

• S650 Series memory cards in native TLC are covered by a 3-year warranty

• S750 cards configured as pSLC are covered by a 5-year warranty

Conclusion and Key Takeaways

The new ATP S650/S750 Series SD/microSD cards meet the high endurance, low latency, and built-to-last data storage requirements of dashcams and digital video recorders (DVRs), as well as surveillance systems, autonomous vehicles, and other write-intensive applications.

• High endurance ensures long time recording. ATP memory cards are built for non-stop video recording, offering high endurance with over 109K hours of continuous recording.

• Low latency for critical recording within 1 second. High-endurance memory cards built for dashcam recording ensure high levels of data integrity. They are ready to record within less than 1 second and can write 50% faster than consumer-rated memory cards.

• Data integrity protection with Read Retry, Auto Read Calibration, and Read Disturb Protector makes sure that stored data remain error-free even in the face of reference voltage shifts or read disturbances.

• Sudden power failure solution. ATP Sudden-Power-Off-Recovery (SPOR) mechanism helps keep data safe and accessible even when unexpected power supply loss happens.

• With ATP's manufacturing capabilities to customize firmware and hardware, as well as its solid warranty policy, dashcam/DVR/surveillance camera vendors as well as their customers can rest assured in ATP's high-endurance memory cards.

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