efm-decoder-f2

EFM T-values to F2 Section Decoder

Overview

efm-decoder-f2 takes T-values as input (supplied by a tool such as ld-decode) and decodes them into F2 sections. Each section contains 98 F2 frames representing 1/75th of a second of data.

The tool handles the initial stages of EFM decoding, converting raw T-values through channel frames and F3 frames to produce F2 sections with basic error correction.

Usage

efm-decoder-f2 [options] <input.efm> <output.f2>

Options

• -h, --help - Display help information
• -v, --version - Display version information
• -d, --debug - Show debug output
• -q, --quiet - Suppress info and warning messages
• --show-f3 - Show F3 frame data
• --show-f2 - Show F2 frame data
• --show-tvalues-debug - Show T-values to channel decoding debug
• --show-channel-debug - Show channel to F3 decoding debug
• --show-f3-debug - Show F3 to F2 section decoding debug
• --show-f2-correct-debug - Show F2 section correction debug
• --show-all-debug - Show all debug output
• --no-timecodes - Process input EFM data with no timecodes (may increase error rates)

Arguments

• input - Input EFM file containing T-values
• output - Output F2 section file

Processing Pipeline

The decoding sequence performed by efm-decoder-f2:

1. T-values → Channel bit stream conversion (from EFM file or stdin)
2. Channel frames → 588-bit frames with sync patterns
3. F3 Frames → 33 symbols of 8-bits each (264 bits total)
4. F2 Sections → Groups of 98 F2 frames with CIRC parity
5. F2 Section Correction → Basic error detection and correction

Unix Pipelining: efm-decoder-f2 supports stdin/stdout using -, making it the starting point for EFM processing pipelines.

Technical Details

T-Values

T-values range from T3 to T11, representing different EFM event periods:

• T3 = 100 (shortest event)
• T4 = 1000
• T5 = 10000
• …
• T11 = 10000000000 (longest event)

Channel Frames

Each 588-bit channel frame contains:

• Sync Header: 24 channel bits
• Merging bits: 3 channel bits
• Control byte: 14 channel bits
• Merging bits: 3 channel bits
• Data bytes 1-32: 32 × (14+3) = 544 channel bits

F2 Sections

Each F2 section represents 1/75th of a second and contains:

• 98 F2 frames of corrected data
• Associated subcode metadata
• CIRC parity for error detection/correction

Output Format

The output F2 section file contains binary data that can be processed by:

• efm-decoder-d24 - For further decoding to Data24 format
• efm-stacker-f2 - For multi-source error correction