From a847f37d43e4571ddc848172caa71e49c087eebe Mon Sep 17 00:00:00 2001
From: Jason Smith <jason.inet@gmail.com>
Date: Sun, 19 Jul 2020 19:53:29 -0700
Subject: [PATCH] Reduce Step Smoothing ceiling to 50% CPU usage (#18719)
---
Marlin/src/module/stepper.cpp | 6 +++---
Marlin/src/module/stepper.h | 6 ++++--
2 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/Marlin/src/module/stepper.cpp b/Marlin/src/module/stepper.cpp
index 16ff134923..2a9e4dae21 100644
--- a/Marlin/src/module/stepper.cpp
+++ b/Marlin/src/module/stepper.cpp
@@ -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
diff --git a/Marlin/src/module/stepper.h b/Marlin/src/module/stepper.h
index 6ae5076cd2..4665f2dc01 100644
--- a/Marlin/src/module/stepper.h
+++ b/Marlin/src/module/stepper.h
@@ -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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