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eMMC: Low-Power Mobile Storage for Smartwatches

By Zachi Friedman, Product Marketing Manager, Synopsys

Today’s connected world is exploding with the Internet-of-Things (IoT) designs across many applications and is exemplified by the advent of wearable devices like smartwatches. The tremendous rise of IoT designs has created many opportunities for designers to deliver differentiated and feature-rich systems beyond mobile devices. The industry is also starting to focus more on wearable devices like smartwatches.

Smartwatches in particular are getting the attention of consumers. Figure 1 shows the global wearable device unit shipments forecast and smartwatches are estimated to ship over 100 million units by 2019. Consequently, SoC designers and system architects are scrambling to include the latest features and bring their differentiated smartwatches to market as quickly as possible. Although smartwatches are considered to be add-on accessories now, some analysts see smartwatches becoming the next smartphones in the very near future, consolidating many discrete functions into a single device.

Figure 1: Global wearable device unit shipments forecast [1]

The Evolution and Making of Smartwatches

After several failed attempts in the 1990s and 2000s, the smartwatch went into a 10-year hibernation until the incredibly successful Kickstarter campaign by Pebble in 2012, raising $10.3M by 68,929 ‘backer’ pledges – the beginning of the smartwatch era. More than one million Pebble watches have sold since 2012. Following Pebble’s success, companies like Samsung, LG and Motorola introduced Android-based smartwatches that were compatible with Android smartphones and began to enjoy the same success. Most recently Apple introduced its own smartwatch called the Apple Watch. According to Business Insider, the Apple Watch is enjoying the biggest smartwatch success so far with one million pre-orders in the first weekend in the United States alone and an estimated 2.3 million units since pre-orders opened. According to Morgan Stanley’s Katy Huberty, “Apple could sell 36 million of its smartwatches over the first 12 months they’re on the market.” The Apple Watch is compatible with the iPhone only and seems to be the most successful smartwatch, yet other companies are quickly catching up and improving their smartwatches’ design and functionality. Since there are more Android-based phones in the global market today, Android-based smartwatches are likely to eventually sell more units (Figure 2).

Figure 2: Global smartphone shipments share Q1 2015 [2]

The Inside of a Smartwatch

The first Pebble used an ARM® Cortex® M3 processor, 128 KB of RAM and 4 to 8 MB of flash storage. Today, smartwatches use dual- or quad-core ARM processors, 512 MB of RAM, and 4 to 8 GB of flash storage. The flash storage is used for the OS, apps, user data, music files, etc. The multi-chip package (MCP) highlighted in the red frame in Figure 3 is SK Hynix H9TU32A4GDMC-LRKGM which packs 512 MB LPDDR2 + 4 GB eMMC in a single package. The processor is a Qualcomm Snapdragon 400 SoC. The hardware specifications are very similar to, if not exactly the same as a mid-tier smartphone in a much smaller package.

Figure 3: Inside of the LG Watch Urbane [3]

eMMC is the Low-Power Mobile Storage Solution for Smartwatches

The most popular mobile storage solution is embedded MultiMediaCard (eMMC). eMMC, a managed NAND flash, is smaller than earlier technologies, making it ideal for small-packaged wearable devices like smartwatches. The components of eMMC are: the eMMC interface, flash memory, and flash memory controller. The components are available from multiple vendors in industry-standard ball grid array (BGA) packages. eMMC uses a discrete controller to hide the complexity of managing the flash memory. By using the eMMC interface, SoC designers benefit from the simplified flash memory interface design and a qualification process that result in reduced time-to-market. Also, the SoC design is future-proofed against the frequent changes in NAND flash component supply and designers can take advantage of faster and less costly eMMC ICs as they become available.

The eMMC interface is designed for low-power devices and implemented mainly in mobile SoCs. It only requires 11 pins to connect to the SoC. The eMMC 5.1 specification allows for fast transfer speeds of up to 400 MB/s, and includes a Command Queuing mechanism used to improve random reads/writes. Samsung’s recently published data highlights the advantages of implementing eMMC:

Capacities: 4 - 128 GB
Sequential R/W: 250/125 MB/s ^[4]
Random R/W: 11,000 / 13,000 IOPS ^[4]

Synopsys Solutions

The JEDEC eMMC specification brings many advantages to IoT SoC designers and system architects – fast time-to-market, high performance, future-proof design and multi-source availability. With the Synopsys DesignWare SD/eMMC Host Controller IP, designers can integrate a single core into their SoC that supports eMMC as well as SD for additional storage options. By supporting the latest specifications, designers can leverage the same SoC design for multiple target applications and markets.

Synopsys also offers a mobile storage interface solution that is based on the JEDEC Unified Flash Storage (UFS) specification. The IP delivers additional performance and feature advantages to mobile applications. Many designers incorporate both UFS and eMMC into the same IoT SoC to give their customers multiple options of mobile storage solution to choose from. Read more about Synopsys’ mobile storage solutions.