SSD Controller Verification

This article provides insights into considerations for SSD Controller Functional Verification.

Introduction

The content is a summarized compilation of knowledge gained from the presentation by Vikas Tomar at Flash Memory Summit 2019. The original PDF file can be downloaded here.

Notes

What to verify?

• Link Level verification (PCIe)
  • Interrupts (MSI, MSIx)
  • PCIe power management (Various Power saving states)
  • Resets
• NVMe Controller Register Level verification
  • Register values
  • Action on register access
• Queue Interface
  • Queue creation/deletion, Doorbell, Empty/Full conditions
  • Queue location and data access
  • Queue starving*
• Data transfer between Host and controller
  • Data Access direction
  • Extra RD/WR on PCIe interface*
• Command Level
  • Admin and IO command
  • Autonomous commands like Abort, Event notifications
  • Possible completion status
• Data structure access
  • PRP (Offsets for PRP1 and PRP2)
  • SGL (Various Descriptors)
• Data structure Values
  • Identify data structures
  • Name space data structures
  • Log pages access
• Feature verification
• Error handling verification

Verification Challenges

• Large Configurations space
  • Behavior of a NVMe operation depends on the combination of various parameter
  • Similarly NVMe SSD can show different performance statistics depending upon
    • Feature enabled by host
    • Queues created by host
    • Parameters related to data transfer selected by host
• Extensive feature support
• Interoperability and Conformance affected by
  • Large configuration space
  • New features
  • Various platforms
• Stimulus generation
  • Impossible to create directed scenarios
  • Randomization helps but do not solve the problem
• Debug
  • Hard to investigate a suspicious transaction

Test Plans

• Controller configuration Test plan
  • SSD Name space (NS DS)
  • Command support
• Host configuration Test plan
  • Covering the possible host configurations
• NVMe Protocol Events Test Plan
  • Specification mapped feature wise Test plan covering
    • Controller register space field access
    • Queue operations
    • PCIe Features
    • NVMe Features
• Standard Compliance test plan

Summary

SSD controller verification is a complex task, encompassing various types of operations. It is considered challenging, even when focusing solely on functional correctness. Customizing SSD controllers for entrepreneurial purposes can further complicate the process to meet heightened performance requirements.