diff --git a/.gitignore b/.gitignore
index 07f5511..54afbaa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,6 +24,7 @@ extras/tests/pc_based/fas_common.h
 extras/tests/pc_based/*.gnuplot
 extras/tests/pc_based/*_test
 extras/tests/pc_based/test.log
+extras/tests/pc_based/*.png
 extras/tests/simavr_based/*/result.txt
 extras/tests/simavr_based/*/x.vcd
 extras/tests/simavr_based/test*sd*/src
diff --git a/extras/tests/pc_based/RampChecker.h b/extras/tests/pc_based/RampChecker.h
index 2a3cc90..ccfec37 100644
--- a/extras/tests/pc_based/RampChecker.h
+++ b/extras/tests/pc_based/RampChecker.h
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <string.h>
 
 class RampChecker {
  public:
@@ -18,6 +19,7 @@ class RampChecker {
   uint32_t ticks_since_last_step;
   float avg_accel;
   FILE *gp_file;
+  char filename[100];
 
   void next_ramp() {
     increase_ok = true;
@@ -40,13 +42,17 @@ class RampChecker {
     next_ramp();
   }
   void start_plot(char *fname) {
+    int n = strlen(fname) - 8; // remove .gnuplot
+    strncpy(filename, fname, n);
+    filename[n] = 0;
     gp_file = fopen(fname, "w");
     fprintf(gp_file, "$data <<EOF\n");
   }
   void finish_plot() {
     if (gp_file != NULL) {
       fprintf(gp_file, "EOF\n");
-      fprintf(gp_file, "set term x11 size 1600, 800\n");
+      fprintf(gp_file, "set term pngcairo size 1600, 800\n");
+      fprintf(gp_file, "set output \"%s.png\"\n", filename);
       fprintf(gp_file, "set multiplot layout 2,2\n");
       fprintf(gp_file, "set title \"speed [steps/s] over time [s]\"\n");
       fprintf(gp_file, "plot $data using 1:2 with lines notitle\n");
@@ -58,7 +64,7 @@ class RampChecker {
               "set title \"averaged (!) acceleration [steps/s*s] over time "
               "[s]\"\n");
       fprintf(gp_file, "plot $data using 1:5 with lines notitle\n");
-      fprintf(gp_file, "pause -1\n");
+      //fprintf(gp_file, "pause -1\n");
       fclose(gp_file);
       gp_file = NULL;
     }
diff --git a/extras/tests/pc_based/test_15.cpp b/extras/tests/pc_based/test_15.cpp
new file mode 100644
index 0000000..4ce86b1
--- /dev/null
+++ b/extras/tests/pc_based/test_15.cpp
@@ -0,0 +1,119 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "FastAccelStepper.h"
+#include "StepperISR.h"
+
+char TCCR1A;
+char TCCR1B;
+char TCCR1C;
+char TIMSK1;
+char TIFR1;
+unsigned short OCR1A;
+unsigned short OCR1B;
+
+StepperQueue fas_queue[NUM_QUEUES];
+
+void inject_fill_interrupt(int mark) {}
+void noInterrupts() {}
+void interrupts() {}
+
+#include "RampChecker.h"
+
+class FastAccelStepperTest {
+ public:
+  void init_queue() {
+    fas_queue[0].read_idx = 0;
+    fas_queue[1].read_idx = 0;
+    fas_queue[0].next_write_idx = 0;
+    fas_queue[1].next_write_idx = 0;
+  }
+
+  void ramp(uint8_t forward_planning, uint32_t expected_steps) {
+    init_queue();
+    FastAccelStepper s = FastAccelStepper();
+    s.init(NULL, 0, 0);
+    RampChecker rc = RampChecker();
+    assert(0 == s.getCurrentPosition());
+
+    uint32_t speed_us = 1000000 / 3600;
+    assert(s.isQueueEmpty());
+    s.setSpeedInUs(speed_us);
+    s.setAcceleration(320);
+    s.setForwardPlanningTimeInMs(forward_planning);
+    s.fill_queue();
+    assert(s.isQueueEmpty());
+    float old_planned_time_in_buffer = 0;
+
+    char fname[100];
+    float sum_planning_time = 0;
+    float points = 0;
+    snprintf(fname, 100, "test_15_%dms.gnuplot", forward_planning);
+    rc.start_plot(fname);
+    s.runForward();
+    for (int i = 0; i < 2000; i++) {
+      if (i == 1000) {
+        printf("Change speed\n");
+        s.setSpeedInUs(10000);
+        s.applySpeedAcceleration();
+      }
+      if (true) {
+        printf(
+            "Loop %d: Queue read/write = %d/%d    Target pos = %d, Queue End "
+            "pos = %d  QueueEmpty=%s\n",
+            i, fas_queue[0].read_idx, fas_queue[0].next_write_idx,
+            s.targetPos(), s.getPositionAfterCommandsCompleted(),
+            s.isQueueEmpty() ? "yes" : "no");
+      }
+      if (!s.isRampGeneratorActive()) {
+        break;
+      }
+      s.fill_queue();
+      uint32_t from_dt = rc.total_ticks;
+      while (!s.isQueueEmpty()) {
+        rc.increase_ok = true;
+        rc.decrease_ok = true;
+        rc.check_section(
+            &fas_queue[0].entry[fas_queue[0].read_idx & QUEUE_LEN_MASK]);
+        fas_queue[0].read_idx++;
+      }
+      uint32_t to_dt = rc.total_ticks;
+      float planned_time = (to_dt - from_dt) * 1.0 / 16000000;
+      printf("planned time in buffer: %.6fs\n", planned_time);
+      sum_planning_time += planned_time;
+      points += 1.0;
+      // This must be ensured, so that the stepper does not run out of
+      // commands
+      assert((i == 0) || (old_planned_time_in_buffer > 0.005));
+      old_planned_time_in_buffer = planned_time;
+      // stop after
+      if (rc.total_ticks > TICKS_PER_S * 40) {
+        break;
+      }
+    }
+    rc.finish_plot();
+    // test(!s.isRampGeneratorActive(), "too many commands created");
+    printf("current position = %d\n", s.getCurrentPosition());
+    test(s.getCurrentPosition() > expected_steps - 10, "stepper runs too slow");
+    test(s.getCurrentPosition() < expected_steps + 10, "stepper runs too fast");
+    printf("Total time  %f\n", rc.total_ticks / 16000000.0);
+    float avg_time = sum_planning_time / points * 1000.0;
+    printf("Average planning time: %f ms\n", avg_time);
+    test(avg_time < forward_planning + 1, "too much forward planning");
+
+#if (TEST_CREATE_QUEUE_CHECKSUM == 1)
+    printf("CHECKSUM for %d/%d/%d: %d\n", steps, travel_dt, accel, s.checksum);
+#endif
+  }
+};
+int main() {
+  FastAccelStepperTest test;
+  // run the ramp twice with 20 and with 5ms planning time.
+  // the ramp will change speed after half of the loops.
+  // The 5ms ramp will not have 20ms coasting in the buffer and as such runs much shorter.
+  test.ramp(20, 76936);
+  test.ramp(5, 11273);
+  printf("TEST_15 PASSED\n");
+  return 0;
+}