User report: on the solar-tracker project (5218f9e3) only one servo
moved and the log showed `ch=0 duty=X% gpio=12` (wrong — servoPan was
attached to GPIO 13) and `ch=1 ... gpio=-1` (servoTilt's channel
never resolved).
Root cause traced through the GPIO Matrix dump: the firmware does
exactly what the Arduino-ESP32 Servo library says — `ledcAttachPin(
13, 0)` writes signal 71 (LEDC_HS_SIG_OUT0) into `gpio_out_sel[13]`,
and `ledcAttachPin(12, 1)` writes signal 72 (LEDC_HS_SIG_OUT1) into
`gpio_out_sel[12]`. Per the ESP32 Technical Reference Manual section
4.11, Table 4-3:
71 .. 78 → LEDC HS channels 0..7
79 .. 86 → LEDC LS channels 0..7
The legacy worker code at esp32_worker.py:426 used the off-by-one
range `72 <= signal <= 87` with `ledc_ch = signal - 72`. The mistake
masked itself for single-servo projects because the 0x5000 duty
callback's channel index was internally consistent with the bogus
math, so the duty STILL reached the correctly-routed pin (just
labelled wrong). The new SignalRouter unit tests caught the
discrepancy the moment two servos drove distinct channels: signal
71 (HS_CH0, gpio 13) was REJECTED by the off-by-one filter and
signal 72 (HS_CH1, gpio 12) was misclassified as channel 0.
When I ported the legacy range into `esp32_signals.SIG_LEDC_HS_CH0_OUT_IDX`
the bug came along for the ride. Fix both modules:
* `backend/app/services/esp32_signals.py`: HS 71-78, LS 79-86.
* `frontend/src/simulation/esp32-signals.ts`: mirror.
* tests updated; 20 backend + 23 frontend pass.
After deploy the user's two servos will resolve to their declared
pins:
ch=0 duty=X% gpio=13 (servoPan, was wrongly emitting gpio=12)
ch=1 duty=X% gpio=12 (servoTilt, was wrongly emitting gpio=-1)
This is also why the multi-servo blink "patch" in commit 77bf897
appeared to help: with both pins ALIASED to the same channel via
the off-by-one, the broadcast fallback was the only thing producing
ANY movement on the second servo at all.
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