Feature: Medical electronics
(2) IntelligentScan and DataRefresh IntelligentScan and DataRefresh are self-testing and self- monitoring methods. Te execution of write and read commands on a NAND cell is a process of electrical discharging and charging. Let us assume that a new NAND cell stores 100 electrons when
written to. Over time, repeated write and erase events will volatilise the cell, reducing its capacitance. Tis reduces the number of electrons stored by a write command from, say, 100 to 80, then to 70, 60, and so on. When the stored charge erodes so much that it falls below a critical threshold, the controller can no longer read the data correctly, resulting in data corruption and loss. Te IntelligentScan function is responsible for checking whether
the stored charge has declined below its threshold value. If it has, it reads out the data bit and rewrites it via the ECC engine; DataRefresh then recharges the cell to restore the NAND cell’s voltage to the correct level.
(3) E2E (End-to-End) Data Path Protection Te function of the E2E Data Path Protection is to verify that the data is correct and to avoid providing incorrect data to the host. When data is written to the SSD, it normally passes through
DRAM and SRAM before being stored in NAND Flash. When the data is read, it returns via the same path. Data can get corrupted at any stage, either by the component
itself or by environmental factors such as high temperature, interference and radiation. Regardless of the cause, any error in the data will be detected immediately by the E2E Data Path Protection. Tis is because a set of parity bits will be generated when the data is written: before the data is read out, the FerriSSD will calculate the parity bits again. If the two sets of parity bits don’t match, the SSD will immediately start a restoration process. If restoration does not work, it will then immediately notify the host that the data can’t be trusted and is unusable. Tis instruction, called “Command Abort”, prevents the host from using corrupt data and thus stops it from initiating incorrect actions, preventing their impact on operations.
Preventing data leakage For medical purposes it is essential to protect the privacy of patients’ personal data – data stored in a storage device must be kept safe from access and retrieval without proper authorisation. When developing the Ferri series, Silicon Motion paid particular
attention to the encryption of user data. Currently, Ferri products support TCG Opal 2.0 and AES 256-bit encryption – standard hardware technologies that are commonly applied in the medical market. In addition, the growth in the number of IoT applications has led many users to call for firmware protection, to prevent a hacker taking control of the firmware (including the SSD driver), and commanding it to execute abnormal actions, such as decryption. Tis would enable the hacker to steal data or activate ransomware to block the SSD, paralyse the equipment and demand a ransom from the user to unlock it. To counter this threat, Silicon Motion uses an electronic fuse (eFuse), adding a “Digital Signature” function to the FerriSSDs’
firmware and soſtware. Te eFuse provides a protection mechanism that’s inaccessible to outsiders. With a unique set of passwords, eFuse can’t be tampered with or allow the SSD to be accessed without authorisation, since Digital Signature verification can’t be performed. Many medical institutions do not trust standard encryption
technology, believing it doesn’t provide sufficient protection. Users in the medical market can work with Silicon Motion to create a custom “Security Handshake”, which, for example, can be a checkpoint known only to the users, or a set of security chips that store passwords to verify an SSD user’s identity. Te Security Handshake works in the same way as a password or phrase that no outsider would know, preventing hackers from modifying the FerriSSD firmware.
Data protection in harsh environments Harsh environments, such as excessively high temperatures or high levels of electromagnetic noise and radiation, can cause data damage and loss. In the medical field this could be high levels of radioactivity or radiated interference. Reliable operation in those environments calls for hardware and firmware customisation to strengthen the equipment’s protection against phenomena such as electrostatic discharge, electromagnetic interference and electromagnetic susceptibility. Preventing damage to medical instruments caused by interference ensures continued patient safety. As well as the FerriSSD products, Silicon Motion also provides
embedded storage solutions with an eMMC or UFS interface: the Ferri-eMMC and Ferri-UFS products extend the choice of embedded storage devices available to medical equipment manufacturers.
www.electronicsworld.co.uk March 2023 33
Harsh environments, such as high levels of electromagnetic noise and radiation, can cause data damage and loss
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