Fix PWM motor-role double-counting in pwmEnsureEnoughtMotors()

[sensei-hacker]

Summary

Pass 1 of pwmEnsureEnoughtMotors() in src/main/drivers/pwm_mapping.c overcounts motor-only outputs that share a physical timer: a group of n shared-timer outputs that are already motor-only at the start of pass 1 inflates the motorOnlyOutputs counter by 2n - 1 instead of n.

pwmClaimTimer() force-syncs every output sharing a physical timer as soon as the first one is visited. Each sibling then independently satisfies TIM_IS_MOTOR_ONLY when the loop reaches its own index later in the same pass, and gets counted again — pass 1 has no guard against this, unlike pass 2's !TIM_IS_MOTOR_ONLY(...) check for the same class of re-visit.

The inflated count makes pass 2 more conservative than it should be when deciding whether to promote remaining AUTO outputs to motors. This can silently demote an output the user configured as a motor down to servo, with no error, log message, or other indication.

Trigger paths

Both hit an ordinary user, not just unusual target.c authoring:

• Compile-time: target.c declares 2+ channels sharing one physical timer as plain TIM_USE_MOTOR (not TIM_USE_OUTPUT_AUTO) — hit at boot regardless of user action. A survey of the target tree found 34 targets with this pattern (e.g. KROOZX, SPRACINGF7DUAL, IFLIGHT_BLITZ_F7_AIO).
• Runtime: the standard timer_output_mode <timer> MOTORS override, exposed in Configurator's Mixer tab, applied to a physical timer serving 2+ outputs. timerHardwareOverride() applies the override before the TIM_IS_MOTOR_ONLY check, so an override-forced group hits the same inflation as a compile-time-declared one.

Fix

Adds a per-physical-timer timerCounted[] dedup guard to pass 1, so each physical timer's motor-only group is counted exactly once regardless of how many of its channels get individually re-visited later in the same pass — mirroring the de-duplication pass 2 already has.

Branch scope

Confirmed present on release/9.1. Confirmed not present on maintenance-10.x — that branch's pwmEnsureEnoughtMotors() was already replaced by a unified pwmBuildTimerOutputList() (direct per-pad assignment, no separate inflatable counter) as an apparent unintentional side effect of unrelated refactor work, so no maintenance-10.x fix is needed.

Testing

• SITL build (cmake -DSITL=ON, make SITL.elf) compiles cleanly with no new warnings.
• Verified via a deterministic Python port of this exact algorithm (simulate_pwm_roles.py in the INAV harness tooling, not part of this PR) — before the fix, a synthetic 2-channel shared-timer group forced to MOTORS inflated the count to 3 and silently demoted a third output at motorCount=3; after the fix, the group counts correctly as 2 and the third output promotes as expected.

Related Issues

None filed yet — found while debugging PWM/DSHOT output setup on a custom target.

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PR Summary by Qodo

Fix PWM motor-role double-counting in pwmEnsureEnoughtMotors()

🐞 Bug fix 🕐 10-20 Minutes

AI Description

• Prevent pass-1 motor-only output counting from double-counting shared-timer siblings
• Ensure AUTO outputs aren’t conservatively blocked from being promoted to motors
• Align pass-1 counting behavior with pass-2’s existing de-dup logic

Diagram

graph TD
  A["pwmBuildTimerOutputList"] --> B["pwmEnsureEnoughtMotors"] --> C["Pass 1: count motor-only"] --> D["timerCounted[] (by timer2id)"] --> E["pwmClaimTimer"] --> F[("timerHardware table")]
  B --> G["Pass 2: promote AUTO to motors"] --> E
  C --> F
  G --> F

Loading

High-Level Assessment

The chosen approach (dedup motor-only counting by physical timer id in pass 1) is the most direct and lowest-risk fix: it corrects the inflated counter while preserving existing two-pass behavior and matching pass 2’s established de-dup pattern. Considered alternatives like refactoring the algorithm to operate on pre-grouped timers or changing pwmClaimTimer() semantics would be more invasive for the same outcome.

Files changed (1) +9 / -1

Bug fix (1) +9 / -1

pwm_mapping.cDeduplicate pass-1 motor-only counting by physical timer +9/-1

Deduplicate pass-1 motor-only counting by physical timer

• Adds a per-physical-timer timerCounted[] guard in pwmEnsureEnoughtMotors() pass 1. Prevents shared-timer motor-only sibling outputs from being re-counted after pwmClaimTimer() synchronizes the entire timer group, avoiding an inflated motorOnlyOutputs baseline that can block correct AUTO-to-motor promotion in pass 2.

src/main/drivers/pwm_mapping.c

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Code Review by Qodo

🐞 Bugs (1) 📘 Rule violations (0) 📜 Skill insights (0)

1. Motor outputs undercounted 🐞 Bug ≡ Correctness

Description

Pass 1 now de-duplicates motor-only counting per physical timer, but it only adds 1 +
pwmClaimTimer(changed), so a timer whose channels are already TIM_USE_MOTOR contributes just 1
regardless of how many motor pads it has. This undercount can make pass 2 promote
TIM_USE_OUTPUT_AUTO pads to motors and claim whole timers as motor-only, silently removing
servo-capable outputs.

Code

src/main/drivers/pwm_mapping.c[R293-296]

+        if (TIM_IS_MOTOR_ONLY(timHw->usageFlags) && !timerCounted[timer2id(timHw->tim)]) {
+            timerCounted[timer2id(timHw->tim)] = true;
            motorOnlyOutputs++;
            motorOnlyOutputs += pwmClaimTimer(timHw->tim, timHw->usageFlags);

Evidence

pwmClaimTimer() returns only the number of sibling pads whose usageFlags actually change, so for
a timer where all pads are already motor-only, pass 1 will add just motorOnlyOutputs++ (1) and
then mark the timer counted, skipping the remaining motor pads. Pass 2 promotes AUTO pads while
motorOnlyOutputs < motorCount, and promotion claims the entire timer via pwmClaimTimer(); those
newly-claimed siblings won’t be demoted later because the pass-2 branch only runs for
TIM_IS_MOTOR(...) && !TIM_IS_MOTOR_ONLY(...).

A concrete repo example (IFLIGHT_BLITZ_F7_AIO) has 4 motor-only pads on TIM3 plus additional
AUTO outputs on other timers, so the new “count once per timer” behavior can trigger unnecessary
AUTO-to-motor promotion even though sufficient motor pads already exist.

src/main/drivers/pwm_mapping.c[260-317]
src/main/target/IFLIGHT_BLITZ_F7_AIO/target.c[32-45]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`pwmEnsureEnoughtMotors()` pass 1 now uses `timerCounted[]` to avoid double-counting a physical timer, but it still relies on `motorOnlyOutputs++` plus `pwmClaimTimer()`'s **changed** count to represent the number of motor outputs on that timer. If all channels on a timer are already motor-only, `pwmClaimTimer()` returns 0, so the timer contributes only 1 to `motorOnlyOutputs` even if it has 2–4 motor pads.

This can leave `motorOnlyOutputs < motorCount` and cause pass 2 to promote `TIM_USE_OUTPUT_AUTO` pads to motors unnecessarily; because promotion calls `pwmClaimTimer()`, it can claim an entire unrelated timer as motor-only and those siblings will not be demoted later (they no longer match the pass-2 `!TIM_IS_MOTOR_ONLY(...)` guard).

## Issue Context
Example target with 4 motor pads on a single timer plus AUTO pads:
- `IFLIGHT_BLITZ_F7_AIO` has 4x `TIM_USE_MOTOR` on `TIM3` and additional `TIM_USE_OUTPUT_AUTO` on `TIM1`/`TIM4`, so after this change pass 1 counts the 4 TIM3 motors as **1**, potentially triggering pass-2 promotion of AUTO outputs.

## Fix Focus Areas
- src/main/drivers/pwm_mapping.c[260-317]
- src/main/target/IFLIGHT_BLITZ_F7_AIO/target.c[32-45]

## Suggested fix approach
When encountering the first motor-only pad for a physical timer (i.e., when `timerCounted[timerId]` is false), compute the number of usable pads for that timer and add that count once, instead of adding `1 + pwmClaimTimer(changed)`.

Concretely:
1. Compute `timerId = timer2id(timHw->tim)` once.
2. If motor-only and not yet counted:
  - Count pads that share `timHw->tim` (optionally excluding conflicts via `checkPwmTimerConflicts()` if the intent is “usable motor outputs”).
  - Add that pad-count to `motorOnlyOutputs`.
  - Call `pwmClaimTimer()` to sync flags, but do **not** use its return value for the motor output count.

This preserves de-duplication while keeping the counter accurate for timers where channels were already motor-only.

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1. Motor outputs undercounted 🐞 Bug ≡ Correctness

Pass 1 now de-duplicates motor-only counting per physical timer, but it only adds 1 +
pwmClaimTimer(changed), so a timer whose channels are already TIM_USE_MOTOR contributes just 1
regardless of how many motor pads it has. This undercount can make pass 2 promote
TIM_USE_OUTPUT_AUTO pads to motors and claim whole timers as motor-only, silently removing
servo-capable outputs.

Agent Prompt

## Issue description
`pwmEnsureEnoughtMotors()` pass 1 now uses `timerCounted[]` to avoid double-counting a physical timer, but it still relies on `motorOnlyOutputs++` plus `pwmClaimTimer()`'s **changed** count to represent the number of motor outputs on that timer. If all channels on a timer are already motor-only, `pwmClaimTimer()` returns 0, so the timer contributes only 1 to `motorOnlyOutputs` even if it has 2–4 motor pads.

This can leave `motorOnlyOutputs < motorCount` and cause pass 2 to promote `TIM_USE_OUTPUT_AUTO` pads to motors unnecessarily; because promotion calls `pwmClaimTimer()`, it can claim an entire unrelated timer as motor-only and those siblings will not be demoted later (they no longer match the pass-2 `!TIM_IS_MOTOR_ONLY(...)` guard).

## Issue Context
Example target with 4 motor pads on a single timer plus AUTO pads:
- `IFLIGHT_BLITZ_F7_AIO` has 4x `TIM_USE_MOTOR` on `TIM3` and additional `TIM_USE_OUTPUT_AUTO` on `TIM1`/`TIM4`, so after this change pass 1 counts the 4 TIM3 motors as **1**, potentially triggering pass-2 promotion of AUTO outputs.

## Fix Focus Areas
- src/main/drivers/pwm_mapping.c[260-317]
- src/main/target/IFLIGHT_BLITZ_F7_AIO/target.c[32-45]

## Suggested fix approach
When encountering the first motor-only pad for a physical timer (i.e., when `timerCounted[timerId]` is false), compute the number of usable pads for that timer and add that count once, instead of adding `1 + pwmClaimTimer(changed)`.

Concretely:
1. Compute `timerId = timer2id(timHw->tim)` once.
2. If motor-only and not yet counted:
   - Count pads that share `timHw->tim` (optionally excluding conflicts via `checkPwmTimerConflicts()` if the intent is “usable motor outputs”).
   - Add that pad-count to `motorOnlyOutputs`.
   - Call `pwmClaimTimer()` to sync flags, but do **not** use its return value for the motor output count.

This preserves de-duplication while keeping the counter accurate for timers where channels were already motor-only.

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools