docs: FT8 TX audio pipeline notes#95
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Captures the two non-obvious gotchas that just took a day to diagnose: 1. lateStartSkipMs must threshold against (15s - 12.64s) = 2.36s of slack, not the cycle boundary. Wrong: chops the leading Costas array off every on-time transmission. (PR #93) 2. libusb iso OUT packet length must be (rate*ch*bps)/1000, NOT the endpoint's wMaxPacketSize. Wrong: device clocks samples ~4% fast and FT8 tones land off the WSJT-X 6.25Hz grid. AudioTrack path is unaffected because the kernel UAC driver does this math. (PR #94) Both failure modes are *silent* — the rig keys, audio is audible on the rig speaker, ALC looks right, but receivers see noise. Without this note in the project instructions, the next person (or the next Claude Code session) re-walks the entire diagnostic chain from debug.log → resampler audit → external WebSDR confirmation. Also fixes the stale package name throughout — applicationId moved from `com.bg7yoz.ft8cn` to `radio.ks3ckc.ft8af` at some point, but the adb pull / logcat / pidof examples in CLAUDE.md still pointed at the old name, so they would silently produce empty results. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Adds an FT8 TX audio pipeline section to CLAUDE.md capturing the two non-obvious failure modes diagnosed today (PR #93 and PR #94), so future debugging sessions don't have to walk the entire chain again.
Also fixes the stale applicationId reference (com.bg7yoz.ft8cn -> radio.ks3ckc.ft8af) -- the adb pull / pidof / logcat --pid examples in CLAUDE.md were silently producing empty results because the package name moved at some point but the docs didn't.
Notes captured
Both failure modes are silent at the rig -- keying works, audio is audible, ALC looks right, receivers see noise.
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