c-from-scratch

Learn to build safety-critical systems in C.

Not "Hello World". Real kernels. Mathematical rigour. Zero dependencies.

"Math → Structs → Code"

Philosophy

Most tutorials teach you to write code that seems to work.
This course teaches you to write code that provably works.

The method:

1. Define the problem mathematically
2. Prove correctness formally
3. Design structs that embody the proof
4. Transcribe the math into C
5. Test against the contracts

┌─────────────────────────────────────────────────────────────┐
│                    THE APPROACH                             │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│   Problem  ──►  Math Model  ──►  Proof  ──►  Structs        │
│                                                │            │
│                                                ▼            │
│                           Verification  ◄──  Code           │
│                                                             │
└─────────────────────────────────────────────────────────────┘

The Seven Foundation Modules

Module	Question	Role	Tests
Pulse	Does it exist?	Sensor	✓
Baseline	Is it normal?	Sensor	18/18
Timing	Is it regular?	Sensor	✓
Drift	Is it trending toward failure?	Sensor	15/15
Consensus	Which sensor to trust?	Judge	17/17
Pressure	How to handle overflow?	Buffer	16/16
Mode	What do we do about it?	Captain	17/17

Plus: Integration Example — All modules working together.

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The Safety Stack

┌─────────────────────────────────────────────────────────────────────┐
│                    MODULE 7: MODE MANAGER                           │
│                       "The Captain"                                 │
│   Decides: What mode? What actions allowed?                         │
└─────────────────────────────────────────────────────────────────────┘
                              ↑
┌─────────────────────────────────────────────────────────────────────┐
│                    MODULE 6: PRESSURE                               │
│                       "The Buffer"                                  │
└─────────────────────────────────────────────────────────────────────┘
                              ↑
┌─────────────────────────────────────────────────────────────────────┐
│                    MODULE 5: CONSENSUS                              │
│                       "The Judge"                                   │
└─────────────────────────────────────────────────────────────────────┘
                              ↑
          ┌───────────────────┼───────────────────┐
          ▼                   ▼                   ▼
┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
│   CHANNEL 0     │ │   CHANNEL 1     │ │   CHANNEL 2     │
│  Pulse → Base   │ │  Pulse → Base   │ │  Pulse → Base   │
│  → Timing       │ │  → Timing       │ │  → Timing       │
│  → Drift        │ │  → Drift        │ │  → Drift        │
│   "Sensors"     │ │   "Sensors"     │ │   "Sensors"     │
└─────────────────┘ └─────────────────┘ └─────────────────┘

---

Module Overview

Modules 1-4: The Sensors

Module	Question	Key Insight
Pulse	Is it alive?	Existence must be proven continuously
Baseline	Is it normal?	"Normal" must be learned, not assumed
Timing	Is it regular?	Jitter indicates system stress
Drift	Is it trending?	"Temperature is normal but rising too fast"

Module 5: The Judge

Consensus — Triple Modular Redundancy voting.

"With THREE clocks, we can outvote the liar."

Module 6: The Buffer

Pressure — Bounded queue with backpressure.

"Only bounded queues let you choose deliberately."

Module 7: The Captain

Mode — System orchestrator with permissions matrix.

"Sensors report. The Captain decides."

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Core Properties

Every module is:

• Closed — No external dependencies at runtime
• Total — Handles all possible inputs
• Deterministic — Same inputs → Same outputs
• O(1) — Constant time, constant space
• Contract-defined — Behaviour is specified, not implied

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Getting Started

# Clone
git clone https://github.com/williamofai/c-from-scratch.git
cd c-from-scratch

# Try any module
cd projects/pulse
make && make test && make demo

# Or run the full integration
cd projects/integration
make run

Start with Pulse Lesson 1: The Problem.

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Specification

See SPEC.md for the complete framework specification:

• Core principles
• Module structure
• Contract definitions
• Composition rules
• Certification alignment (DO-178C, IEC 62304, ISO 26262)

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Who This Is For

• Developers building safety-critical software
• Systems programmers who want provable correctness
• Students learning C the rigorous way
• Anyone tired of "it works on my machine"

Prerequisites

• Basic C syntax (variables, functions, structs)
• Comfort with command line
• Willingness to think before coding

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Author

William Murray — 30 years UNIX systems engineering

• GitHub: @williamofai
• LinkedIn: William Murray
• Website: speytech.com

License

MIT — See LICENSE

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"Sensors report. The Captain decides."