PicoLM

Run a 1-billion parameter LLM on a $10 board with 256MB RAM.
Pure C. Zero dependencies. One binary. No Python. No cloud.

echo "Explain gravity" | ./picolm model.gguf -n 100 -j 4

---

The Perfect Match: PicoLM + PicoClaw

PicoLM was built as the local brain for PicoClaw — an ultra-lightweight AI assistant in Go that runs on $10 hardware. Together, they form a fully offline AI agent — no cloud, no API keys, no internet, no monthly bills.

Every other LLM provider needs the internet. PicoLM doesn't.

The Hardware	The Architecture
$9.90 — that's the entire server	PicoLM powers the LLM box in PicoClaw's agent loop

Why they're a perfect fit

| | Cloud Provider (OpenAI, etc.) | PicoLM (Local) | |---|---|---| | Cost | Pay per token, forever | Free forever | | Privacy | Your data sent to servers | Everything stays on-device | | Internet | Required for every request | Not needed at all | | Latency | Network round-trip + inference | Inference only | | Hardware | Needs a $599 Mac Mini | Runs on a $10 board | | Binary | N/A | ~80KB single file | | RAM | N/A | 45 MB total |

How it works

PicoClaw's agent loop spawns PicoLM as a subprocess. Messages come in from Telegram, Discord, or CLI — PicoClaw formats them into a chat template, pipes the prompt to picolm via stdin, and reads the response from stdout. When tools are needed, --json grammar mode guarantees valid JSON even from a 1B model.

Telegram / Discord / CLI
        │
        ▼
   ┌──────────┐    stdin: prompt     ┌───────────┐
   │ PicoClaw │ ──────────────────►  │  picolm   │
   │   (Go)   │ ◄──────────────────  │   (C)     │
   └──────────┘    stdout: response  │ + model   │
        │                            └───────────┘
        ▼                            45 MB RAM
   User gets reply                   No internet

Quick setup

# 1. Build PicoLM
cd picolm && make native    # or: make pi (Raspberry Pi)
2. Download model (one-time, 638 MB)
make model
3. Build PicoClaw
cd ../picoclaw && make deps && make build
4. Configure (~/.picoclaw/config.json)

{
  "agents": {
    "defaults": {
      "provider": "picolm",
      "model": "picolm-local"
    }
  },
  "providers": {
    "picolm": {
      "binary": "~/.picolm/bin/picolm",
      "model": "~/.picolm/models/tinyllama-1.1b-chat-v1.0.Q4_K_M.gguf",
      "max_tokens": 256,
      "threads": 4,
      "template": "chatml"
    }
  }
}

# 5. Chat — fully offline!
picoclaw agent -m "What is photosynthesis?"

Or install everything in one line

curl -sSL https://raw.githubusercontent.com/RightNow-AI/picolm/main/install.sh | bash

Performance on real hardware

| Device | Price | Generation Speed | RAM Used | |--------|-------|-----------------|----------| | Pi 5 (4-core) | $60 | ~10 tok/s | 45 MB | | Pi 4 (4-core) | $35 | ~8 tok/s | 45 MB | | Pi 3B+ | $25 | ~4 tok/s | 45 MB | | Pi Zero 2W | $15 | ~2 tok/s | 45 MB | | LicheeRV Nano | $10 | ~1 tok/s | 45 MB |

JSON tool calling

PicoClaw automatically activates --json grammar mode when it needs structured output. This guarantees syntactically valid JSON even from a 1B parameter model — essential for reliable tool calling on tiny hardware:

picoclaw agent -m "Search for weather in Tokyo"
→ PicoLM generates: {"tool_calls": [{"function": {"name": "web_search", "arguments": "{\"query\": \"weather Tokyo\"}"}}]}

For the full PicoClaw documentation, see the PicoClaw README.

---

What is PicoLM?

PicoLM is a minimal, from-scratch LLM inference engine written in ~2,500 lines of C11. It runs TinyLlama 1.1B (and other LLaMA-architecture models in GGUF format) on hardware that most inference frameworks won't even consider:

• Raspberry Pi Zero 2W ($15, 512MB RAM, ARM Cortex-A53)
• Sipeed LicheeRV ($12, 512MB RAM, RISC-V)
• Raspberry Pi 3/4/5 (1-8GB RAM, ARM NEON SIMD)
• Any Linux/Windows/macOS x86-64 machine

The model file (638MB) stays on disk. PicoLM memory-maps it and streams one layer at a time through RAM. Total runtime memory: ~45MB including the FP16 KV cache.

                    ┌──────────────────────────────────────────┐
   What goes        │         45 MB Runtime RAM                │
   in RAM           │  ┌─────────┐ ┌──────────┐ ┌───────────┐  │
                    │  │ Buffers │ │ FP16 KV  │ │ Tokenizer │  │
                    │  │  1.2 MB │ │ Cache    │ │   4.5 MB  │  │
                    │  │         │ │  ~40 MB  │ │           │  │
                    │  └─────────┘ └──────────┘ └───────────┘  │
                    └──────────────────────────────────────────┘
┌──────────────────────────────────────────┐
   What stays       │        638 MB Model on Disk              │
   on disk          │       (mmap — OS pages in layers         │
   (via mmap)       │        as needed, ~1 at a time)          │
                    └──────────────────────────────────────────┘

---

Features

| Feature | Description | |---------|-------------| | GGUF Native | Reads GGUF v2/v3 files directly — no conversion needed | | K-Quant Support | Q2_K, Q3_K, Q4_K, Q5_K, Q6_K, Q8_0, Q4_0, F16, F32 | | mmap Layer Streaming | Model weights stay on disk; OS pages in one layer at a time | | FP16 KV Cache | Halves KV cache memory (44MB vs 88MB for 2048 context) | | Flash Attention | Online softmax — no O(seq_len) attention buffer needed | | Pre-computed RoPE | cos/sin lookup tables eliminate transcendentals from hot loop | | SIMD Acceleration | ARM NEON (Pi 3/4/5) and x86 SSE2 (Intel/AMD) auto-detected | | Fused Dot Products | Dequantize + dot-product in one pass — no intermediate buffer | | Multi-threaded matmul | Parallel matrix-vector multiply across CPU cores | | Grammar-Constrained JSON | --json flag forces valid JSON output (for tool calling) | | KV Cache Persistence | --cache saves/loads prompt state — skip prefill on re-runs | | BPE Tokenizer | Score-based byte-pair encoding, loaded from GGUF metadata | | Top-p Sampling | Temperature + nucleus sampling with configurable seed | | Pipe-friendly | Reads prompts from stdin: echo "Hello" \| ./picolm model.gguf | | Zero Dependencies | Only libc, libm, libpthread. No external libraries. | | Cross-platform | Linux, Windows (MSVC), macOS. ARM, x86-64, RISC-V. |

---

Quick Start

One-liner install (Raspberry Pi / Linux)

curl -sSL https://raw.githubusercontent.com/RightNow-AI/picolm/main/install.sh | bash

This will: 1. Detect your platform (ARM64, ARMv7, x86-64) 2. Install build dependencies (gcc, make, curl) 3. Build PicoLM with optimal SIMD flags for your CPU 4. Download TinyLlama 1.1B Q4_K_M (638 MB) 5. Run a quick test 6. Generate PicoClaw config 7. Add picolm to your PATH

Build from source

git clone https://github.com/rightnow-ai/picolm.git
cd picolm/picolm
Auto-detect CPU (enables SSE2/AVX on x86, NEON on ARM)
make native
Download a model
make model
Run it
./picolm /opt/picolm/models/tinyllama-1.1b-chat-v1.0.Q4_K_M.gguf \
    -p "The meaning of life is" -n 100

Build on Windows (MSVC)

cd picolm
build.bat
picolm.exe model.gguf -p "Hello world" -n 50

Platform-specific builds

make native      # x86/ARM auto-detect (recommended for local machine)
make pi          # Raspberry Pi 3/4/5 (64-bit ARM + NEON SIMD)
make pi-arm32    # Pi Zero / Pi 1 (32-bit ARM)
make cross-pi    # Cross-compile for Pi from x86 (static binary)
make riscv       # RISC-V (Sipeed LicheeRV, etc.)
make static      # Static binary for single-file deployment
make debug       # Debug build with symbols, no optimization

---

Usage

PicoLM — ultra-lightweight LLM inference engine
Usage: picolm  [options]
Generation options:
  -p     Input prompt (or pipe via stdin)
  -n        Max tokens to generate (default: 256)
  -t      Temperature (default: 0.8, 0=greedy)
  -k      Top-p / nucleus sampling (default: 0.9)
  -s        RNG seed (default: 42)
  -c        Context length override
  -j        Number of threads (default: 4)
Advanced options:
  --json         Grammar-constrained JSON output mode
  --cache  KV cache file (saves/loads prompt state)

Examples

Basic generation:

./picolm model.gguf -p "Once upon a time" -n 200

Greedy decoding (deterministic, temperature=0):

./picolm model.gguf -p "The capital of France is" -n 20 -t 0
Output: Paris. It is the largest city in France and...

Chat with TinyLlama (ChatML format):

./picolm model.gguf -n 200 -t 0.7 -p "<|user|>
What is photosynthesis?
<|assistant|>
"

Force JSON output (for tool calling / structured data):

./picolm model.gguf --json -t 0.3 -n 100 -p "<|user|>
Return the current time as JSON.
<|assistant|>
"
Output: {"time": "12:00 PM"}

Pipe from stdin:

echo "Explain quantum computing in one sentence" | ./picolm model.gguf -n 50

KV cache — skip repeated prefill:

# First run: processes prompt + saves cache
./picolm model.gguf --cache prompt.kvc -p "Long system prompt here..." -n 50

Second run: loads cache, skips prompt prefill (74% faster)
./picolm model.gguf --cache prompt.kvc -p "Long system prompt here..." -n 50
Output: "Skipping 25 cached prompt tokens"

Multi-threaded on a Pi 4 (4 cores):

./picolm model.gguf -p "Hello" -n 100 -j 4

---

Performance

Measured on TinyLlama 1.1B Q4_K_M (638 MB model):

| Metric | x86-64 (8 threads) | Pi 4 (4 cores, NEON) | Pi Zero 2W | |--------|--------------------|-----------------------|------------| | Prefill | ~11 tok/s | ~6 tok/s | ~1.5 tok/s | | Generation | ~13 tok/s | ~8 tok/s* | ~2 tok/s* | | Runtime RAM | 45 MB | 45 MB | 45 MB | | First token | ~2.3s | ~4s | ~16s | | Binary size | ~80 KB | ~70 KB | ~65 KB |

*\Estimated with NEON SIMD enabled. Actual numbers depend on SD card speed and thermal throttling.

What makes it fast

 Raw C inference          ████████████░░░░░░░░  13.5 tok/s  (baseline: 1.6)
 + Fused dot products     ████████████████░░░░  (eliminate dequant buffer)
 + Multi-threaded matmul  █████████████████░░░  (4-8 cores in parallel)
 + FP16 KV cache          █████████████████░░░  (halve memory bandwidth)
 + Pre-computed RoPE      ██████████████████░░  (no sin/cos in hot loop)
 + Flash attention        ██████████████████░░  (no O(n) attention alloc)
 + NEON/SSE2 SIMD         ███████████████████░  (4-wide vector ops)
 + KV cache persistence   ████████████████████  (skip prefill entirely)

---

Architecture

                          ┌─────────────────────────────────┐
                          │           picolm.c              │
                          │     CLI + Generation Loop       │
                          └──────┬──────────────┬───────────┘
                                 │              │
                    ┌────────────┘              └────────────┐
                    │                                        │
           ┌────────┴────────┐                    ┌──────────┴──────────┐
           │    model.h/c    │                    │    sampler.h/c      │
           │  GGUF Parser    │                    │  Temperature +      │
           │  mmap Layer     │                    │  Top-p Sampling     │
           │  Streaming      │                    └──────────┬──────────┘
           │  Forward Pass   │                               │
           │  KV Cache I/O   │                    ┌──────────┴──────────┐
           └───┬────────┬────┘                    │    grammar.h/c      │
               │        │                         │  JSON Constraint    │
      ┌────────┘        └───────┐                 │  Logit Masking      │
      │                         │                 └─────────────────────┘
┌─────┴──────┐          ┌───────┴────────┐
│ tensor.h/c │          │ tokenizer.h/c  │
│ matmul     │          │ BPE Encode     │
│ rmsnorm    │          │ Decode         │
│ softmax    │          │ Vocab Lookup   │
│ rope       │          └────────────────┘
│ silu       │
│ threading  │
└─────┬──────┘
      │
┌─────┴──────┐
│  quant.h/c │
│ Q4_K, Q6_K │
│ Q3_K, Q2_K │
│ FP16, F32  │
│ NEON + SSE │
│ Fused Dots │
└────────────┘

The LLaMA Forward Pass (what happens for each token)

Input Token
    │
    ▼
┌───────────────┐
│ Embedding     │  Dequantize row from token_embd → x[2048]
│ Lookup        │
└───────┬───────┘
        │
        ▼
┌───────────────┐  ×22 layers
│ RMSNorm       │─────────────────────────────────────────┐
│               │                                         │
│ Q = xb @ Wq   │  Matrix-vector multiply (quantized)     │
│ K = xb @ Wk   │  Store K,V in FP16 KV cache             │
│ V = xb @ Wv   │                                         │
│               │                                         │
│ RoPE(Q, K)    │  Rotary position encoding (table lookup)│
│               │                                         │
│ Attention     │  Flash attention with online softmax    │
│ (GQA 32→4)    │  Grouped-query: 32 Q heads, 4 KV heads  │
│               │                                         │
│ x += Out@Wo   │  Output projection + residual           │
│               │                                         │
│ RMSNorm       │                                         │
│               │                                         │
│ SwiGLU FFN    │  gate=SiLU(xb@Wg), up=xb@Wu             │
│               │  x += (gate*up) @ Wd                    │
└───────┬───────┘─────────────────────────────────────────┘
        │
        ▼
┌───────────────┐
│ Final RMSNorm │
│ x @ W_output  │─→ logits[32000]
└───────┬───────┘
        │
        ▼
┌───────────────┐
│ Grammar Mask  │  (if --json: force valid JSON structure)
│ Sample Token  │  temperature → softmax → top-p → pick
└───────────────┘

---

Memory Budget

For TinyLlama 1.1B Q4_K_M with 2048 context length:

| Component | Size | Notes | |-----------|------|-------| | FP16 KV cache | ~40 MB | 22 layers x 2 x 2048 x 256 x 2 bytes | | Tokenizer | ~4.5 MB | 32K vocab strings + scores + sorted index | | Activation buffers | ~0.14 MB | x, xb, xb2, q, hb, hb2 | | Logits buffer | ~0.12 MB | 32000 x 4 bytes | | Dequant scratch | ~0.02 MB | Max(n_embd, n_ffn) floats | | Norm weights (pre-dequant) | ~0.35 MB | 45 norm vectors x 2048 x 4 bytes | | RoPE tables | ~0.03 MB | cos + sin x 2048 x 32 entries | | Total runtime | ~45 MB | | | | | | | Model file (on disk) | 638 MB | Memory-mapped, ~1 layer in RAM at a time |

With 512 context (for constrained devices):

| Component | Size | |-----------|------| | FP16 KV cache | ~10 MB | | Everything else | ~5 MB | | Total | ~15 MB |

---

Optimizations Deep-Dive

PicoLM implements 9 optimizations that brought generation speed from 1.6 tok/s to 13.5 tok/s on x86, with even larger gains expected on ARM with NEON:

1. ARM NEON SIMD

4-wide float vector operations for all hot paths. Example: dequantizing Q4_K nibbles with vmovl_u8 → vmovl_u16 → vcvtq_f32_u32, and RoPE with interleaved vld2q_f32 / vst2q_f32.

2. x86 SSE2 SIMD

Auto-detected on Intel/AMD. 4-wide __m128 operations for dot products, RMSNorm, and vector operations.

3. FP16 KV Cache

Key and value vectors stored as 16-bit floats instead of 32-bit. Halves KV cache memory from ~88MB to ~44MB. Conversion uses software fp32_to_fp16() / fp16_to_fp32() — no hardware FP16 support required.

4. Pre-computed RoPE Tables

Sine and cosine values for all positions computed once at model load. The forward pass does a table lookup instead of calling sinf() / cosf() / powf() 64 times per token.

5. Flash Attention (Online Softmax)

Single-pass attention with running maximum rescaling. Eliminates the O(seq_len) attention score buffer — critical for long contexts on memory-constrained devices.

6. Fused Dequantize + Dot Product

vec_dot_q4_K_f32() dequantizes and accumulates in one pass. No intermediate float buffer for the weight row. Reduces memory traffic by ~50% for matmul.

7. Multi-threaded Matrix Multiply

matmul() distributes output rows across threads using pthreads. Each thread processes its chunk independently with fused dot products. Scales linearly up to ~8 cores.

8. Grammar-Constrained JSON

The --json mode pre-analyzes every token in the vocabulary at load time (brace delta, bracket delta, quote parity). During generation, it masks logits to guarantee syntactically valid JSON — essential for tool-calling with small models.

9. KV Cache Persistence

--cache file.kvc saves the FP16 KV cache state after prompt processing. On the next run with the same prompt, it loads the cache and skips prefill entirely. 74% latency reduction for repeated system prompts.

---

Supported Models

PicoLM supports any LLaMA-architecture model in GGUF format:

| Model | Parameters | GGUF Size (Q4_K_M) | RAM Needed | |-------|-----------|---------------------|------------| | TinyLlama 1.1B | 1.1B | 638 MB | ~45 MB | | Llama 2 7B | 7B | 4.1 GB | ~200 MB | | Phi-2 | 2.7B | 1.6 GB | ~90 MB |

Recommended for embedded: TinyLlama 1.1B Q4_K_M — fits comfortably on devices with 256MB+ RAM.

Supported quantization formats

Q2_K Q3_K Q4_K Q4_0 Q5_K Q6_K Q8_0 F16 F32

---

File Structure

PicoLM/
├── README.md              ← you are here
├── BLOG.md                ← technical deep-dive blog post
├── install.sh             ← one-liner Pi installer
│
├── picolm/                ← the inference engine (pure C)
│   ├── picolm.c           ← CLI entry point, generation loop (273 lines)
│   ├── model.h/c          ← GGUF parser, mmap, forward pass (146 + 833 lines)
│   ├── tensor.h/c         ← matmul, rmsnorm, softmax, rope (44 + 298 lines)
│   ├── quant.h/c          ← dequantization, SIMD kernels (140 + 534 lines)
│   ├── tokenizer.h/c      ← BPE tokenizer (32 + ~200 lines)
│   ├── sampler.h/c        ← temperature + top-p sampling (19 + ~100 lines)
│   ├── grammar.h/c        ← JSON grammar constraints (64 + 175 lines)
│   ├── Makefile           ← build targets for all platforms
│   └── build.bat          ← Windows MSVC build script
│
└── tinyllama-1.1b-chat-v1.0.Q4_K_M.gguf  ← model file (638 MB, not in git)

Total C source: ~2,500 lines. That's the entire inference engine — GGUF parsing, mmap, dequantization, matrix math, attention, tokenization, sampling, and grammar constraints.

---

How It Works

The mmap trick

Traditional inference engines load the entire model into RAM. PicoLM doesn't. Instead:

1. The model file is memory-mapped (mmap on Linux/macOS, MapViewOfFile on Windows) 2. Weight pointers point directly into the mapped file — no copying 3. During the forward pass, each layer's weights are accessed sequentially 4. The OS automatically pages in the needed weights and evicts old ones 5. madvise(MADV_SEQUENTIAL) hints the access pattern to the kernel

Result: A 638MB model runs on a device with 256MB RAM. Only ~30MB of the model is in physical memory at any time.

Quantization

Weights are stored in 4-bit quantized format (Q4_K_M). For TinyLlama:

• Original: 1.1B parameters x 4 bytes = 4.4 GB
• Q4_K: 1.1B parameters x ~0.56 bytes = 638 MB
• Quality loss: Minimal — Q4_K preserves 6-bit scales per 32-weight sub-block

Grouped-Query Attention (GQA)

TinyLlama uses 32 query heads but only 4 key/value heads. Each KV head is shared by 8 query heads. This reduces KV cache size by 8x compared to full multi-head attention.

---

Building & Testing

Prerequisites

| Platform | Requirements | |----------|-------------| | Linux/Pi | gcc, make (install via apt install build-essential) | | macOS | Xcode Command Line Tools (xcode-select --install) | | Windows | Visual Studio Build Tools (cl.exe) |

Verify your build

# Build
make native
Test with greedy decoding (deterministic output)
./picolm model.gguf -p "The capital of France is" -n 20 -t 0
Expected: "Paris. It is the largest city in France..."
Test JSON mode
./picolm model.gguf --json -p "Return JSON with name and age" -n 50 -t 0.3
Expected: valid JSON like {"name": "...", "age": ...}
Test KV cache
./picolm model.gguf --cache test.kvc -p "Hello" -n 10 -t 0
./picolm model.gguf --cache test.kvc -p "Hello" -n 10 -t 0
Second run should say "Skipping N cached prompt tokens"

Memory verification

PicoLM prints memory stats to stderr:

Memory: 1.17 MB runtime state (FP16 KV cache separate)

Total = runtime state + FP16 KV cache. For TinyLlama with 2048 context: ~45 MB.

---

FAQ

Q: Can this run Llama 2 7B? A: Yes, if you have enough RAM for the KV cache (~1.4 GB for 7B with 4096 context). The model file stays on disk via mmap. On a Pi 4 with 4GB RAM, it works but is slow (~1-2 tok/s).

Q: Why not use llama.cpp? A: llama.cpp is excellent but requires ~200MB+ for the runtime on small models, has complex build dependencies, and targets desktop/server use cases. PicoLM is purpose-built for embedded: 45MB RAM, 80KB binary, zero dependencies.

Q: Is the output quality good? A: TinyLlama 1.1B is a small model — it handles simple tasks (Q&A, summarization, basic reasoning, JSON generation) well. It won't match GPT-4, but it runs on a $10 board with no internet. For structured output, the --json grammar mode guarantees valid JSON regardless of model quality.

Q: What about GPU acceleration? A: PicoLM is CPU-only by design. The target hardware ($10-15 boards) doesn't have GPUs. On x86/ARM CPUs, SIMD (NEON/SSE2) provides meaningful speedup.

Q: Can I use a different model? A: Any LLaMA-architecture GGUF model works. Download from HuggingFace and point PicoLM at it. Recommended quantizations: Q4_K_M (best quality/size balance) or Q2_K (smallest, lower quality).

---

Roadmap

• [ ] AVX2/AVX-512 kernels for x86 (2-4x generation speed on modern CPUs)
• [ ] Speculative decoding with a draft model
• [ ] Context sliding window (infinite generation beyond max_seq_len)
• [ ] Weight pruning for further memory reduction
• [ ] Continuous batching for server mode
• [ ] Mistral / Phi architecture support

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Technical Blog

For a detailed wr