In recent blog posts, we’ve presented ways to validate your managed flash device1 designs (UFS2 or e-MMC3) prior to mass production by conducting a signal integrity analysis, as well as a power integrity analysis. Another critical analysis of the validation process is performing a thorough protocol analysis. Skipping this step can lead to subtle bugs, unexpected failures, and a lot of wasted time. Let me dive into why protocol analysis is vital, what it involves and why it is important as part of the validation process.
Protocol analysis is about capturing, decoding and reviewing the command and data transactions between your host controller and managed flash device. It ensures that every command, sequence and setting align with JEDEC® standards. Even if your device seems to operate fine, hidden protocol violations can lead to failures, and in some cases, they only show up under specific conditions. It is highly recommended that protocol exchanges are evaluated from the very first initialization sequence all the way through normal operations. This analysis ensures that each device operates in accordance with the device specifications and system design, pinpointing potential issues in hardware or software.
If you’re validating UFS devices, there are six key sequences you need to analyze:
- Link Startup Sequence: When you power on your UFS device, the host controller and device exchange capabilities and initialize communication. It is important to capture and review these exchanges to ensure both sides are within specification.
- Boot Sequence: Managed flash device platforms may implement the boot function differently, so it is important to verify that the actual boot sequence matches the intended protocol exchanges. A discrepancy can cause a boot failure or unpredictable behavior.
- Power Mode Change Sequence: UFS supports multiple power modes and gear levels, ranging from low to high speed, to scale performance as needed. It is important to check all protocol exchanges during power mode changes to confirm they are executed correctly.
- Power Cycle Sequence: Before removing power, it’s imperative that all volatile data is safely written to the device’s NAND flash memory. To prevent potentially harmful data loss, verify that the power-down sequence is working correctly.
- Normal Operation: Protocol exchanges between the host controller and UFS device need to be analyzed to ensure proper device initialization and correct behavior under normal operating conditions. Different access patterns are used to confirm that the commands sent by the host controller are executed and the UFS device provides timely responses.
- Specialized Features: Whether it’s a standard JEDEC feature or a vendor-specific feature (like RPMB access or device provisioning), the driver commands and sequences need to be analyzed to confirm that they are working correctly.
If you’re validating e-MMC devices, there are two key sequences you need to analyze:
- Power On to Boot Sequence: Use an e-MMC protocol analyzer to capture the sequential series of commands (CMD0, CMD1, CMD2, etc.) issued by the host controller during a device boot up. Since each command has a specific purpose, all commands issued need to be verified and in sequence. If an error or time out occurs during boot up, reviewing the command sequence is your first debugging step.
- Power On After Boot Sequence: The commands that were issued by the host controller and sent to the device after initialization also need to be verified. Missing or unexpected commands can cause the device to misbehave or trigger kernel errors. In addition, verification that standard device operations occur and the host controller can send several commands is part of this analysis.
Final Thoughts
When validating your UFS or e-MMC device design prior to mass production, protocol analysis isn’t optional - it’s essential and a safeguard for your device’s long-term reliability. Protocol analysis means capturing, decoding and reviewing every command and data exchange between your host controller and your device, making sure everything aligns with JEDEC standards. Even if your device seems to work, protocol violations can lurk beneath the surface and cause problems later. By thoroughly analyzing protocol exchanges, you can catch issues early, ensure compliance, and deliver robust UFS and e-MMC solutions that stand up to real-world use.
Things to Think About:
- Never assume that a successful boot means everything is fine. Just because your device boots or runs doesn’t mean there aren’t hidden protocol issues.
- Use the right tools. Protocol analyzers are your best friend for capturing and decoding protocol exchanges.
- Reference the standards. Always check the applicable JEDEC specs and your device’s technical data sheets.
- Consult your vendors. When in doubt, reach out for guidance. For KIOXIA America, Inc. contact the sales department.
More information available here.
FOOTNOTES:
1 A managed flash device combines raw NAND flash memory and an intelligent controller in one integrated package, enabling internal memory management.
2 Universal Flash Storage (UFS) devices are based on the UFS specification, of which, the v4.1 specification is the current release issued by JEDEC and announced in January 2025.
3 Embedded MultiMediaCard (e-MMC) is a specification developed by JEDEC® for mobile applications. The current release is v5.1, published in February 2015.
JEDEC is a registered trademark of the Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association. All other company names, product names and service names may be trademarks of third-party companies.
DISCLAIMERS:
Information in this blog, including product specifications, tested content, and assessments are current and believed to be accurate as of the date of this publication, but is subject to change without prior notice. Technical and application information contained here is subject to the most recent applicable KIOXIA product specifications.