34 lines
1.4 KiB
Markdown
34 lines
1.4 KiB
Markdown
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---
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type: guidelines
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---
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# Core services guidelines
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## 1. Listen-only until `obd-poller` exists
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- Nothing here opens a CAN socket for writing. The recorder only reads, and the
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host brings `can_pcan` up listen-only.
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- `obd-poller` will be the single writer. Until it lands, any transmit is a bug.
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## 2. Capture never waits
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- A frame missed is gone. Producers hand frames to the writer without blocking;
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what doesn't fit is **counted**, recorded as an event, and never silently lost.
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- Capture reads SocketCAN and gpsd directly. It does not depend on the broker, a
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display, or any other service being up.
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## 3. Every failure leaves complete files
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- Append, flush and `fdatasync` about once a second. Power loss costs at most the
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last second.
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- Replace files by write-temp, fsync, rename. Never rewrite in place.
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- Anything found half-done at startup is repaired or marked, not deleted.
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## 4. Raw stays raw
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- Recordings are `candump -L` text plus the gpsd JSON as received, so `can-utils`,
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`canplayer` and anything already written against the first captures keep working.
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- Decoding happens downstream of the recording, never instead of it.
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## 5. Time is evidence, not truth
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- The car unit's clock can boot stale and be stepped mid-drive. Record what is
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needed to correct it later (sync state, monotonic time, observed steps, GNSS
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time beside local receive time) rather than trusting it.
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## 6. To be added
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