---
name: schunix-crash-screen
description: "PSOGM crash screen lives in kernel/core/panic.c; test it with `echo c > /proc/sysrq` and tools/crashshot.ps1"
metadata: 
  node_type: memory
  type: project
  originSessionId: a665e14b-86bd-4b41-a228-51377f3e9225
  modified: 2026-08-03T15:09:42.189Z
---

**The crash screen is `kernel/core/panic.c`** (rewritten 2026-08-03; it used to
live inside `console.c`). **PSOGM — Purple Screen of Guru Meditation.** Solid
purple, big white `:(` drawn from primitives, Windows-style left-aligned
headline and field table, then a raw call-chain dump. Nexoniarz picked this
after a first attempt that dimmed the desktop and floated a dark panel with a
cartoon emoji over it — **the emoji and the muted palette read as out of
place**; the name says purple screen, so it is one.

A "Stop code" field is derived from the panic message (uppercased up to the
first colon: `"sysrq: crash requested"` → `SYSRQ`), so no call site has to
supply one.

**To see it, crash on purpose:**

```
echo c > /proc/sysrq          # from inside Schunix
```

**To photograph it:** `pwsh -File tools/crashshot.ps1` (or `make crashshot`)
after `make ramroot`. It boots, fills the screen with real output, crashes,
and pulls a PPM out through QEMU's monitor on TCP 55555. Convert with
`convert build/crashscreen.ppm build/crashscreen.png` — ImageMagick is in the
WSL Fedora box as `convert`, not `magick`.

Why the trigger exists at all: **the crash screen is the one part of the system
you cannot look at by using the system**, so without a deliberate trigger it is
only ever seen when something is already wrong, and it quietly rots.

**Three things that will bite anyone editing it:**

- There is no libm. `isqrt` in panic.c uses Newton's method iterated *while the
  estimate decreases*; the obvious "stop when it stops changing" version does
  not terminate, because on a non-square it settles into a two-cycle
  (`isqrt(3)` alternates 1, 2, 1, 2...). That shipped once and hung the panic
  handler with the screen half drawn — a hang with no way to find out why.

- `vga_draw_char` fills the *background* of every glyph with `vga_bg`. Drawing
  panel text without setting `vga_set_bg(PSOGM_PANEL)` first puts every line in
  a cream-coloured box.
- `cprintf` writes to the framebuffer as well as the serial line, so the serial
  report scrolls straight over the panel. `cons_panic_mode()` sets
  `cons_serial_only`, which is what keeps the two apart — paint order alone
  does not.

The serial copy is the one that survives, and it is what `tools/bootcheck.ps1`
reads. It is also all you get when the panic happens before there is a
framebuffer. See [[schunix-verify-by-driving-shell]].