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pwm iteration limit to avoid float math accuracy loss (#4578)

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Matthew Kennedy 2022-09-13 18:16:35 -07:00 committed by GitHub
parent 2042d9b0b6
commit 35997c6318
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1 changed files with 8 additions and 1 deletions
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9
firmware/controllers/system/timer/pwm_generator_logic.cpp
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@ -142,7 +142,14 @@ void PwmConfig::handleCycleStart() {
pwmCycleCallback(this);
}
// Compute the maximum number of iterations without overflowing a uint32_t worth of timestamp
uint32_t iterationLimit = (0xFFFFFFFF / periodNt) - 2;
uint32_t iterationLimitInt32 = (0xFFFFFFFF / periodNt) - 2;
// Maximum number of iterations that don't lose precision due to 32b float (~7 decimal significant figures)
// We want at least 0.01% timing precision (aka 1/10000 cycle, 0.072 degree for trigger stimulator), which
// means we can't do any more than 2^23 / 10000 cycles = 838 iterations before a reset
uint32_t iterationLimitFloat = 838;
uint32_t iterationLimit = minI(iterationLimitInt32, iterationLimitFloat);
efiAssertVoid(CUSTOM_ERR_6580, periodNt != 0, "period not initialized");
efiAssertVoid(CUSTOM_ERR_6580, iterationLimit > 0, "iterationLimit invalid");