score: Add _IO_Relax()

4 files changed, 63 insertions, 0 deletions

diff --git a/cpukit/Makefile.am b/cpukit/Makefile.am
index 0b760eb031..9aec91b4ae 100644
--- a/cpukit/Makefile.am
+++ b/cpukit/Makefile.am
@@ -1033,6 +1033,7 @@ librtemscpu_a_SOURCES += score/src/wkspacemallocinitunified.c
 librtemscpu_a_SOURCES += score/src/wkstringduplicate.c
 librtemscpu_a_SOURCES += score/src/iobase64.c
 librtemscpu_a_SOURCES += score/src/ioprintf.c
+librtemscpu_a_SOURCES += score/src/iorelax.c
 librtemscpu_a_SOURCES += score/src/iovprintf.c
 librtemscpu_a_SOURCES += score/src/isrisinprogress.c
 librtemscpu_a_SOURCES += score/src/condition.c
diff --git a/cpukit/include/rtems/score/io.h b/cpukit/include/rtems/score/io.h
index 97026e46cd..795b682f7c 100644
--- a/cpukit/include/rtems/score/io.h
+++ b/cpukit/include/rtems/score/io.h
@@ -130,6 +130,14 @@ int _IO_Base64url(
  */
 void _IO_Dump_gcov_info( IO_Put_char put_char, void *arg );
 
+/**
+ * @brief Issues a couple of no-operation instructions.
+ *
+ * This function may be used to burn a couple of processor cycles with minimum
+ * impact on the system bus.  It may be used in busy wait loops.
+ */
+void _IO_Relax( void );
+
 /** @} */ 
 
 #ifdef __cplusplus
diff --git a/cpukit/score/src/iorelax.c b/cpukit/score/src/iorelax.c
new file mode 100644
index 0000000000..f37d848605
--- /dev/null
+++ b/cpukit/score/src/iorelax.c
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+
+/**
+ * @file
+ *
+ * @ingroup RTEMSScoreIO
+ *
+ * @brief This source file contains the implementation of _IO_Relax().
+ */
+
+/*
+ * Copyright (C) 2021 embedded brains GmbH (http://www.embedded-brains.de)
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <rtems/score/io.h>
+#include <rtems/score/cpuimpl.h>
+
+void _IO_Relax( void )
+{
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+  _CPU_Instruction_no_operation();
+}
diff --git a/spec/build/cpukit/librtemscpu.yml b/spec/build/cpukit/librtemscpu.yml
index c9ad5ea729..f03af274a4 100644
--- a/spec/build/cpukit/librtemscpu.yml
+++ b/spec/build/cpukit/librtemscpu.yml
@@ -402,6 +402,7 @@ source:
 - cpukit/score/src/iobase64.c
 - cpukit/score/src/iodumpgcovinfo.c
 - cpukit/score/src/ioprintf.c
+- cpukit/score/src/iorelax.c
 - cpukit/score/src/iovprintf.c
 - cpukit/score/src/isr.c
 - cpukit/score/src/isrisinprogress.c