From 7f7a3e8f70c46a2a5a5ef120909c8211840ef5cb Mon Sep 17 00:00:00 2001
From: Sebastian Huber <sebastian.huber@embedded-brains.de>
Date: Thu, 29 Jun 2017 14:36:26 +0200
Subject: tests: Move busy loop to test support

Update #3056.
---
 cpukit/libmisc/Makefile.am            |   1 +
 cpukit/libmisc/testsupport/test.h     |  18 +++++-
 cpukit/libmisc/testsupport/testbusy.c | 107 ++++++++++++++++++++++++++++++++++
 3 files changed, 125 insertions(+), 1 deletion(-)
 create mode 100644 cpukit/libmisc/testsupport/testbusy.c

(limited to 'cpukit/libmisc')

diff --git a/cpukit/libmisc/Makefile.am b/cpukit/libmisc/Makefile.am
index d8fa47a2a5..6772dd1673 100644
--- a/cpukit/libmisc/Makefile.am
+++ b/cpukit/libmisc/Makefile.am
@@ -174,6 +174,7 @@ libstringto_a_SOURCES = stringto/stringtodouble.c stringto/stringtofloat.c \
 noinst_LIBRARIES += libtestsupport.a
 libtestsupport_a_SOURCES =
 libtestsupport_a_SOURCES += testsupport/testbeginend.c
+libtestsupport_a_SOURCES += testsupport/testbusy.c
 libtestsupport_a_SOURCES += testsupport/testextension.c
 libtestsupport_a_SOURCES += testsupport/testparallel.c
 
diff --git a/cpukit/libmisc/testsupport/test.h b/cpukit/libmisc/testsupport/test.h
index a32e2c42c1..d9ac6caf91 100644
--- a/cpukit/libmisc/testsupport/test.h
+++ b/cpukit/libmisc/testsupport/test.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2016 embedded brains GmbH.  All rights reserved.
+ * Copyright (c) 2014, 2017 embedded brains GmbH.  All rights reserved.
  *
  *  embedded brains GmbH
  *  Dornierstr. 4
@@ -260,6 +260,22 @@ void rtems_test_parallel(
   size_t job_count
 );
 
+/**
+ * @brief Performs a busy loop with the specified iteration count.
+ *
+ * This function is optimized to not perform memory accesses and should have a
+ * small jitter.
+ *
+ * @param[in] count The iteration count.
+ */
+void rtems_test_busy(uint_fast32_t count);
+
+/**
+ * @brief Returns a count value for rtems_test_busy() which yields roughly a
+ * duration of one clock tick.
+ */
+uint_fast32_t rtems_test_get_one_tick_busy_count(void);
+
 /** @} */
 
 #ifdef __cplusplus
diff --git a/cpukit/libmisc/testsupport/testbusy.c b/cpukit/libmisc/testsupport/testbusy.c
new file mode 100644
index 0000000000..2d34a805dc
--- /dev/null
+++ b/cpukit/libmisc/testsupport/testbusy.c
@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2014, 2017 embedded brains GmbH.  All rights reserved.
+ *
+ *  embedded brains GmbH
+ *  Dornierstr. 4
+ *  82178 Puchheim
+ *  Germany
+ *  <rtems@embedded-brains.de>
+ *
+ * The license and distribution terms for this file may be
+ * found in the file LICENSE in this distribution or at
+ * http://www.rtems.org/license/LICENSE.
+ */
+
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <rtems/test.h>
+#include <rtems.h>
+
+static uint_fast32_t estimate_busy_loop_maximum( void )
+{
+  uint_fast32_t units = 0;
+  uint_fast32_t initial = rtems_clock_get_ticks_since_boot();
+
+  while ( initial == rtems_clock_get_ticks_since_boot() ) {
+    ++units;
+  }
+
+  return units;
+}
+
+static uint_fast32_t wait_for_tick_change( void )
+{
+  uint_fast32_t initial = rtems_clock_get_ticks_since_boot();
+  uint_fast32_t now;
+
+  do {
+    now = rtems_clock_get_ticks_since_boot();
+  } while ( now == initial );
+
+  return now;
+}
+
+/*
+ * It is important that we use actually use the same rtems_test_busy() function
+ * at the various places, since otherwise the obtained maximum value might be
+ * wrong.  So, the compiler must not inline this function.
+ */
+RTEMS_NO_INLINE void rtems_test_busy( uint_fast32_t count )
+{
+  uint_fast32_t i = 0;
+
+  do {
+    __asm__ volatile ("");
+    ++i;
+  } while ( i < count );
+}
+
+uint_fast32_t rtems_test_get_one_tick_busy_count( void )
+{
+  uint_fast32_t last;
+  uint_fast32_t now;
+  uint_fast32_t a;
+  uint_fast32_t b;
+  uint_fast32_t m;
+
+  /* Choose a lower bound */
+  a = 1;
+
+  /* Estimate an upper bound */
+
+  wait_for_tick_change();
+  b = 2 * estimate_busy_loop_maximum();
+
+  while ( true ) {
+    last = wait_for_tick_change();
+    rtems_test_busy( b );
+    now = rtems_clock_get_ticks_since_boot();
+
+    if ( now != last ) {
+      break;
+    }
+
+    b *= 2;
+    last = now;
+  }
+
+  /* Find a good value */
+  do {
+    m = ( a + b ) / 2;
+
+    last = wait_for_tick_change();
+    rtems_test_busy( m );
+    now = rtems_clock_get_ticks_since_boot();
+
+    if ( now != last ) {
+      b = m;
+    } else {
+      a = m;
+    }
+  } while ( b - a > 1 );
+
+  return m;
+}
-- 
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