leviathan
45 lines
2.1 KiB
Markdown
45 lines
2.1 KiB
Markdown
# Ford V0 Protocol
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**Rust module:** `src/protocols/ford_v0.rs`
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**Reference:** `REFERENCES/ProtoPirate/protocols/ford_v0.c`
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## Overview
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Ford V0 uses Manchester encoding at 250/500 µs. 80 bits total: 64-bit key1 + 16-bit key2. CRC is computed via GF(2) matrix multiplication (CRC matrix in code). BS (byte) and “BS magic” are used for encoding and validation. 6 bursts; 4 preamble pairs per burst; 3500 µs gap before data. Flipper-style Manchester: level true → ShortLow/LongLow, level false → ShortHigh/LongHigh.
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## Timing
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| Parameter | Value | Notes |
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|------------|--------|--------------------|
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| Short | 250 µs | ±100 µs (te_delta) |
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| Long | 500 µs | ±100 µs |
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| Gap | 3500 µs| ±250 µs |
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| Min bits | 64 | (key1); 80 total |
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## Encoding
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Manchester: short/low, short/high, long/low, long/high map to events 0–3; state machine emits data bits. First bit after gap is implicit 1; then 79 more bits from Manchester (64 for key1, 16 for key2). key1/key2 sent inverted (~key1, ~key2).
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## Frame Layout (80 bits)
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- **key1 (64 bits):** header byte, serial, button, counter, XOR/parity and mixed nibbles (see decode_ford_v0 in code).
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- **key2 (16 bits):** BS (high byte), CRC (low byte) XOR 0x80.
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CRC is matrix-based over key1 bytes and BS byte; received CRC is key2 low byte XOR 0x80.
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## Decoder Steps
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1. **Reset** — Short HIGH (250 µs) or long HIGH (500 µs) → Preamble (allows re-sync mid-preamble).
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2. **Preamble** — LOW long (500 µs) → PreambleCheck.
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3. **PreambleCheck** — HIGH long → header_count++, back to Preamble; HIGH short → Gap.
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4. **Gap** — LOW ~3500 µs (±250) → Data, set first bit to 1, bit_count=1.
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5. **Data** — Manchester events (short/long × level); add_bit (two 64-bit registers, C-style); at 64 bits form key1 = ~combined, clear; at 80 bits key2 = ~low 16, decode_ford_v0, verify CRC, return.
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## Encoder
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Supported. Builds 6 bursts: short-long, 4 preamble pairs, short-long, gap, then Manchester 80 bits (key1 then key2, inverted). Inter-burst gap long×100.
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## Frequencies
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315 MHz, 433.92 MHz.
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