One event, all the way down.

Pick a moment in a running program and follow it through every layer of the machine at once — on one clock.

The machine is a three-stage RV32I core, synthesised to gates, mapped to Sky130 standard cells, placed and routed. Not the computer in front of you — a real small one we can show completely.

Fathom

One event, followed down every layer of a machine, on one clock. The machine is a three-stage RV32I core (lowRISC Ibex), synthesised to gates, mapped to Sky130 cells, placed and routed. It is not the computer in front of you; every layer is a model of that core and says so in its header.

• ←→ step a cycle · ⇧ ×10 · HomeEnd
• ↓ descend into the next layer · ↑ ascend · Esc all layers
• click a source line, an assembly row, a pipeline column, a gate bar, or a layer's header
• the bottom two layers load on demand (DuckDB-wasm, 18 MB, same-origin)
• agents: window.fathom — describe · seek · descend · ascend · stateAt · trace · loadBottom · history

version · every artifact is precomputed and read-only · no network beyond this origin · ? or Esc closes