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Course contents

  • How to Use This Course
  • The NanoSoC Tour
  • Reading Path
  • SoC Glossary10
  • SoC Metrics Reference
  • SoC Cheatsheet
  • What SoC Integration Is12
  • Architecture and Budgets21
  • Memory Maps and Address Decode26
  • Interconnect and Bus Fabrics26
  • Clock and Reset Architecture24
    • Clock Sources and PLLs
    • Dividers, Muxes and Glitch-Free Switching
    • Clock Gating Architecture
    • Clock Domain Planning
    • Top-Level Crossings
    • Always-On Domain, Wake Policy and a Timer Extension
    • Reset Sources and Reset Tree
    • Reset Sequencing and Release
      • Release Order and Timing
      • Asynchronous Assert, Synchronous Release
      • Release-Order Failure Modes
  • Power Architecture21
  • Interrupts, DMA and Peripherals15
  • Memories, Boot and Security21
  • IP Integration and Handoff21
  • Top-Level Verification and Bring-up21
  • Package, Pads and I/O18
  • Chip Signoff and Tapeout18
  • SoC Interview Prep16
  • Capstone: Integrate NanoSoC14
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←Clock and Reset Architecture
  1. Topics
  2. SoC Design
  3. Clock and Reset Architecture
  4. Reset Sequencing and Release

Part 5 of 14Part 5 of 14/Clock and Reset ArchitectureAll levels

Reset Sequencing and Release

Release order and timing in cycles, async assert with sync release, recovery and removal, and the CPU-early failure.

  • 3topics
  • 3lessons

The rule of the whole topic fits in one line: slaves and fabric first, masters last, with the CPU the last thing to leave reset. This topic turns that line into cycles: the seven-step cold-boot release totalling 53.948 us, the two-flop synchroniser behind every release with a waveform to prove it, and the failure where the CPU wakes before the fabric. For the circuit view see Async Assert, Sync Deassert; for reset ordering across power and warm resets see Reset Sequencing with Power-On and Warm Reset and Release Order Across Domains.

Lesson

After it you can...

Release Order and Timing

Quote the NanoSoC release order in cycles and recompute its total.

Asynchronous Assert, Synchronous Release

Prove per-domain release is synchronous and read the release waveform.

Release-Order Failure Modes

Tell the CPU-early failure and the partial-reset hang as symptom, capture and fix.

Suggested order: top to bottom. Order first, because the synchroniser lesson implements two rows of its table; then the release circuit with its waveform; then the failures, which are all violations of the order. The boot flow after release belongs to the memories and boot section.

Check yourself Why must the CPU leave reset last rather than first?

Everything it touches on its first cycles must already be alive: the fabric to carry its fetches, the ROM to answer them, the bridges settled. A CPU out of reset before its slaves fetches into a fabric that cannot answer.

Expect to write the release table from memory with cycle counts, then defend the order: peripherals, fabric, CPU. The whiteboard reset question scores the order, the holds and the cause register together.

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See also

  • Clock Sources and PLLs
  • Dividers, Muxes and Glitch-Free Switching
  • Clock Gating Architecture