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The SD Association has announced a new standard called microSD Express, which supports the NVMe PCIe protocol to improve overall device performance. Devices using the standard will be able to achieve transfer rates of up to 985 MB / s, thanks to a single PCIe 3.1 support path. New drives will remain backward compatible with older cards: you will be able to read and use old microSD cards in microSD Express slots and microSD Express cards will continue to work with older players.
PCIe 3.1 is PCIe 3.0 with various enhancements to power management, performance, and features. According to the SD association:
PCIe 3.1 includes low-power substations (L1.1, L1.2) that enable low-power implementations of SD Express for the mobile market. In addition, SD Express cards with significantly faster data transfer rates should consume less power than traditional microSD memory cards while maintaining the same maximum power consumption. The cards provide system developers with new options offered by PCIe and NVMe features, such as bus mastering, multiple queue (without locking mechanism), and host memory buffer.
Multiple queues should improve simultaneous I / O performance by reducing lock contention. Mastering the bus allows a component – the microSD card in this case – to communicate with other components without the need for CPU time.
In addition, the host memory buffer (HMB) allows the NVMe device to use a small slice of system RAM to store mapping tables that convert logical memory addresses to physical memory locations in the device. even. Without HMB, the device must either include its own DRAM memory, or store that data on its own NAND flash memory. The first option is the fastest but costs both power and space, while the second is much slower.
HMB is a technique that improves the performance of storing this data in flash, even if it does not really match the performance of a device-embedded DRAM pool. The presentation even suggests that this flexibility could someday work in both directions, allowing host devices to process the microSD card's NAND flash memory to exploit an extension of the system's main memory, in the same way as NAND flash memory. can be used as a DRAM. alternative today.
This is only a brief mention in the presentation and I do not know exactly what circumstances would make sense for this type of buffering, so I would not read much. But it's an interesting ability to see highlighted in the document.
The net result of all this should be microSD cards
which are significantly faster than their predecessors. The maximum power consumption for SD Express cards is 1.8 W, although this is not indicated as typical power consumption. Customers will need to ensure that microSD Express cards are compatible with devices supporting the standard via the PCIe interface, otherwise performance will not reach their theoretical highs. It may take time to see support material on the market, especially if phone manufacturers do not start adding standard support.
While PCIe support for microSD cards can be easily integrated into SoCs and power improvements are as good as the SD Association claims, I was hoping to see the technology adopted. Saving energy is an important feature of modern appliances, especially with energy-saving 5G modems on the horizon.
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