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Decrease ADAPTIVE_STEP_SMOOTHING target to 50% CPU usage #18719

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Jul 20, 2020
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Decrease ADAPTIVE_STEP_SMOOTHING target to 50% CPU usage #18719

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6 changes: 3 additions & 3 deletions Marlin/src/module/stepper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2099,11 +2099,11 @@ uint32_t Stepper::block_phase_isr() {
#if ENABLED(ADAPTIVE_STEP_SMOOTHING)
uint8_t oversampling = 0; // Assume no axis smoothing (via oversampling)
// Decide if axis smoothing is possible
uint32_t max_rate = current_block->nominal_rate; // Get the maximum rate (maximum event speed)
uint32_t max_rate = current_block->nominal_rate; // Get the step event rate
while (max_rate < MIN_STEP_ISR_FREQUENCY) { // As long as more ISRs are possible...
max_rate <<= 1; // Try to double the rate
if (max_rate >= MAX_STEP_ISR_FREQUENCY_1X) break; // Don't exceed the estimated ISR limit
++oversampling; // Increase the oversampling (used for left-shift)
if (max_rate < MIN_STEP_ISR_FREQUENCY) // Don't exceed the estimated ISR limit
++oversampling; // Increase the oversampling (used for left-shift)
}
oversampling_factor = oversampling; // For all timer interval calculations
#else
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6 changes: 4 additions & 2 deletions Marlin/src/module/stepper.h
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Expand Up @@ -229,8 +229,10 @@
#define MAX_STEP_ISR_FREQUENCY_2X ((F_CPU) / ISR_EXECUTION_CYCLES(2))
#define MAX_STEP_ISR_FREQUENCY_1X ((F_CPU) / ISR_EXECUTION_CYCLES(1))

// The minimum allowable frequency for step smoothing will be 1/10 of the maximum nominal frequency (in Hz)
#define MIN_STEP_ISR_FREQUENCY MAX_STEP_ISR_FREQUENCY_1X
// The minimum step ISR rate used by ADAPTIVE_STEP_SMOOTHING to target 50% CPU usage
// This does not account for the possibility of multi-stepping.
// Perhaps DISABLE_MULTI_STEPPING should be required with ADAPTIVE_STEP_SMOOTHING.
#define MIN_STEP_ISR_FREQUENCY (MAX_STEP_ISR_FREQUENCY_1X / 2)

//
// Stepper class definition
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