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Packet & bit fields templates

Packet — Deliberately Wrong: Bits Nobody Claimed

The second teaching artefact. Bits 12 to 19 of a declared two-word layout belong to no field, and the difference between 'reserved' and 'nobody thought about it' is the whole of what a register map is for. The engine marks the run and says how wide it is, rather than drawing a tidy diagram over a hole.

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Interrupt register — with a gap (deliberate)16-bit words · 2 words · 32 bits laid out · 6 fields · ruler shows ABSOLUTE bit indicesLSB-first: bit 0 is the least significant bit of each 16-bit word, drawn rightmost; indices decrease to the right.In both orders the most significant bit of a word is the leftmost column — only the numbering flips.1 layout finding across 6 fields — see the notes.MSBLSBword 0bits 0–15+0B1514131211109876543210word 1bits 16–31+2B31302928272625242322212019181716Sourcebits 0–3 · 4bPrioritybits 4–7 · 4bVectorbits 8–11 · 4bMaskbits 20–23 · 4bStatusbits 24–27 · 4bReservedbits 28–31 = 0unclaimedunclaimedBits 12–19 are claimed by no field — a gap in the layout.

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title "Interrupt register — with a gap (deliberate)"
width 16
bitorder lsb
words 2

0-3:   Source
4-7:   Priority
8-11:  Vector
20-23: Mask
24-27: Status
28-31: Reserved = 0