pid/filter: FAST_CODE annotations and RC command caching#11357
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sensei-hacker wants to merge 2 commits intoiNavFlight:maintenance-9.xfrom
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pid/filter: FAST_CODE annotations and RC command caching#11357sensei-hacker wants to merge 2 commits intoiNavFlight:maintenance-9.xfrom
sensei-hacker wants to merge 2 commits intoiNavFlight:maintenance-9.xfrom
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pidController is FAST_CODE. Its callees that lacked FAST_CODE created
SRAM veneers (trampolines from ITCM to flash) on every call. Annotate
each callee that was audited as genuinely hot:
pid.c:
pTermProcess, dTermProcess, applyItermLimiting,
pidApplySetpointRateLimiting, checkItermLimitingActive,
checkItermFreezingActive, pidRcCommandToAngle, pidRcCommandToRate
smith_predictor.c: applySmithPredictor
filter.c: pt1ComputeRC (static; called from FAST_CODE pt1FilterApply4)
maths.c: constrain, constrainf, scaleRangef
(called from the pid.c functions above; candidates for static inline
in a future refactor, but FAST_CODE resolves the veneer for now)
fc_core.c: getAxisRcCommand
Functions removed from FAST_CODE where no FAST_CODE caller existed
(sin_approx, cos_approx, fast_fsqrtf, failsafeShouldApplyControlInput)
were never added in this tree; no net change for those.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Two independent optimisations for the main PID loop: rcCommand caching (fc_core.c) getAxisRcCommand() and failsafeUpdateRcCommandValues() are now gated on isRXDataNew so they only run when the RX task delivers a fresh frame (~50 Hz) instead of every PID cycle (1 kHz / multirotor rate). rcCommand[] is updated from a small cache on every cycle so the rest of the code is unaffected. pidSumLimit precomputation (pid.c) getPidSumLimit() returns 400 or 500 based on vehicle type and axis — values that are constant for the lifetime of a flight. Add a pidSumLimit field to pidState_t, initialise it once in pidInit(), and replace the two hot-path calls in pidApplyFixedWingRateController and pidApplyMulticopterRateController with a struct field read. getPidSumLimit() is retained for pid_autotune.c (not hot). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
Two performance improvements to the PID hot path, applied in order:
pid/filter: add FAST_CODE to pidController callees— addsFAST_CODEto functions called frompidController()so they land in ITCM (fast RAM) on STM32 targets, eliminating flash-to-ITCM trampoline jumps at 1 kHzfc/pid: avoid recomputing values that change at lower rates— caches RC command values andpidSumLimitso they are only recalculated when new RX data arrives (~50 Hz) rather than every PID loop iteration (~1000 Hz). Also gatesfailsafeUpdateRcCommandValues()behind the same new-data checkFiles Changed
src/main/common/filter.c— FAST_CODEsrc/main/common/maths.c— FAST_CODEsrc/main/fc/fc_core.c— FAST_CODE, RC command cachingsrc/main/flight/pid.c— FAST_CODE, RC command cachingsrc/main/flight/smith_predictor.c— FAST_CODETesting