From 166b4da5516089535d319f00ef0c6989aefa574f Mon Sep 17 00:00:00 2001
From: patacongo <patacongo@42af7a65-404d-4744-a932-0658087f49c3>
Date: Sun, 8 Mar 2009 23:33:41 +0000
Subject: [PATCH] Add support for priority inheritance

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@1581 42af7a65-404d-4744-a932-0658087f49c3
---
 ChangeLog                                |   2 +
 Documentation/NuttX.html                 |   4 +-
 Documentation/NuttxPortingGuide.html     |   9 +-
 Documentation/NuttxUserGuide.html        |  10 +-
 TODO                                     |   6 +-
 arch/arm/src/common/up_reprioritizertr.c |  24 +-
 arch/pjrc-8051/src/up_reprioritizertr.c  |  54 +++--
 arch/sh/src/common/up_reprioritizertr.c  |  24 +-
 arch/sim/src/up_reprioritizertr.c        |  24 +-
 arch/z16/src/common/up_reprioritizertr.c |  24 +-
 arch/z80/src/common/up_reprioritizertr.c |  24 +-
 configs/README.txt                       |   4 +-
 configs/sim/ostest/defconfig             |   3 +-
 examples/ostest/Makefile                 |  32 ++-
 examples/ostest/main.c                   |  12 +-
 examples/ostest/ostest.h                 |   6 +-
 examples/ostest/prioinherit.c            | 292 +++++++++++++++++++++++
 include/nuttx/sched.h                    |   5 +-
 include/pthread.h                        |   6 +-
 include/semaphore.h                      |   5 +-
 sched/os_internal.h                      |   2 +-
 sched/pthread_create.c                   |   6 +-
 sched/pthread_setschedprio.c             |   4 +-
 sched/sched_setparam.c                   |  58 +++--
 sched/sem_destroy.c                      |   8 +-
 sched/sem_post.c                         |  20 +-
 sched/sem_wait.c                         |  40 +++-
 sched/task_restart.c                     |  49 ++--
 sched/task_setup.c                       |   7 +-
 29 files changed, 634 insertions(+), 130 deletions(-)
 create mode 100644 examples/ostest/prioinherit.c

diff --git a/ChangeLog b/ChangeLog
index d183e4f30b8..532f448d6fa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -650,5 +650,7 @@
 	* Restructured parts of the uIP port for correct compilation with ZDS-II
 	* eZ80Acclaim!: Complete basic integration of the eZ80F91 EMAC driver.  The
 	  driver is basically functional and should mature prior to the 0.4.3 release.
+	* Implemented priority inheritance logic for POSIX semaphores.  Because the pthread
+	  mutexes are built on semaphores, they will have this property as well.
 
 
diff --git a/Documentation/NuttX.html b/Documentation/NuttX.html
index fef9520a391..f5000359979 100644
--- a/Documentation/NuttX.html
+++ b/Documentation/NuttX.html
@@ -285,7 +285,7 @@
   <td><br></td>
   <td>
     <p>
-      <li>Realtime, deterministic.</li>
+      <li>Realtime, deterministic, with support for priority inheritance</li>
     </p>
 </tr>
 
@@ -1371,6 +1371,8 @@ nuttx-0.4.3 2009-xx-xx Gregory Nutt &lt;spudmonkey@racsa.co.cr&gt;
 	* Restructured parts of the uIP port for correct compilation with ZDS-II
 	* eZ80Acclaim!: Complete basic integration of the eZ80F91 EMAC driver.  The
 	  driver is basically functional and should mature prior to the 0.4.3 release.
+	* Implemented priority inheritance logic for POSIX semaphores.  Because the pthread
+	  mutexes are built on semaphores, they will have this property as well.
 
 pascal-0.1.3 2009-xx-xx Gregory Nutt &lt;spudmonkey@racsa.co.cr&gt;
 
diff --git a/Documentation/NuttxPortingGuide.html b/Documentation/NuttxPortingGuide.html
index b47cd99dedb..4c3f3ff79d2 100644
--- a/Documentation/NuttxPortingGuide.html
+++ b/Documentation/NuttxPortingGuide.html
@@ -12,7 +12,7 @@
       <h1><big><font color="#3c34ec">
         <i>NuttX RTOS Porting Guide</i>
       </font></big></h1>
-      <p>Last Updated: December 5, 2008</p>
+      <p>Last Updated: March 8, 2009</p>
     </td>
   </tr>
 </table>
@@ -1623,8 +1623,13 @@ The system can be re-made subsequently by just typing <code>make</code>.
     provides /dev/console.  Enables stdout, stderr, stdin.
   </li>
   <li>
-    <code>CONFIG_MUTEX_TYPES</code>: Set to enabled support for recursive and
+    <code>CONFIG_MUTEX_TYPES</code>: Set to enable support for recursive and
     errorcheck mutexes.  Enables <code>pthread_mutexattr_settype()</code>.
+  </li>
+  <li>
+    <code>CONFIG_PRIORITY_INHERITANCE </code>: Set to enable support for
+    priority inheritance on mutexes and semaphores.
+  </li>
 </ul>
 
 <p>
diff --git a/Documentation/NuttxUserGuide.html b/Documentation/NuttxUserGuide.html
index 0dfa64a87bd..5869beedf99 100644
--- a/Documentation/NuttxUserGuide.html
+++ b/Documentation/NuttxUserGuide.html
@@ -13,7 +13,7 @@
       <h1><big><font color="#3c34ec"><i>NuttX Operating System<p>User's Manual</i></font></big></h1>
       <p><small>by</small></p>
       <p>Gregory Nutt<p>
-      <p>Last Updated: November 18, 2008</p>
+      <p>Last Updated: March 8, 2009</p>
     </td>
   </tr>
 </table>
@@ -1718,9 +1718,11 @@ interface of the same name.
 <p>
   Some operating systems avoid priority inversion by <I>automatically</I>
   increasing the priority of the low-priority <I>Task C</I> (the operable
-  buzz-word for this behavior is <I>priority inheritance</I>).  NuttX does not
-  support this behavior.  As a consequence, it is left to the designer to
-  provide implementations that will not suffer from priority inversion.
+  buzz-word for this behavior is <I>priority inheritance</I>).  NuttX
+  supports this behavior, but only if <code>CONFIG_PRIORITY_INHERITANCE</code>
+  is defined in your OS configuration file.  If <code>CONFIG_PRIORITY_INHERITANCE</code>
+  is not defined, then it is left to the designer to provide implementations
+  that will not suffer from priority inversion.
   The designer may, as examples:
 </p>
 <ul>
diff --git a/TODO b/TODO
index ea3e218d3fb..763d0888935 100644
--- a/TODO
+++ b/TODO
@@ -1,7 +1,7 @@
 NuttX TODO List (Last updated February 19, 2009)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-  (7)  Task/Scheduler (sched/)
+  (6)  Task/Scheduler (sched/)
   (1)  Dynamic loader (N/A)
   (2)  Memory Managment (mm/)
   (1)  Signals (sched/, arch/)
@@ -53,10 +53,6 @@ o Task/Scheduler (sched/)
   Status:      Open
   Priority:    Low
 
-  Description: Implement priority inheritance
-  Status:      Open
-  Priority:    Medium, this is a good feature for realtime systems.
-
   Description: Several APIs do not set errno.  Need to review all APIs.
   Status:      Open
   Priority:    Medium, required for standard compliance (but makes the
diff --git a/arch/arm/src/common/up_reprioritizertr.c b/arch/arm/src/common/up_reprioritizertr.c
index b802f2e8484..edc2f9e1f3d 100644
--- a/arch/arm/src/common/up_reprioritizertr.c
+++ b/arch/arm/src/common/up_reprioritizertr.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  *  arch/arm/src/common/up_reprioritizertr.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -85,14 +85,27 @@ void up_reprioritize_rtr(_TCB *tcb, ubyte priority)
 {
   /* Verify that the caller is sane */
 
-  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
-      tcb->task_state > LAST_READY_TO_RUN_STATE ||
-      priority < SCHED_PRIORITY_MIN || 
+#if CONFIG_DEBUG /* We only check parameters when debug is enabled */
+  if (priority < SCHED_PRIORITY_MIN || 
       priority > SCHED_PRIORITY_MAX)
     {
        PANIC(OSERR_BADREPRIORITIZESTATE);
     }
   else
+#endif
+  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
+           tcb->task_state > LAST_READY_TO_RUN_STATE)
+    {
+      /* This is a hack and needs to be fixed.. here some taks is reprioritizing
+       * another task that is not running.  Here we just set the priority of
+       * the task -- BUT some of the other states are also prioritized and the
+       * waiting task should also be re-ordered in the prioritized wiating list.
+       * As a consequence, the other task is still waiting at the lower priority.
+       */
+
+       tcb->sched_priority = priority;
+    }
+  else
     {
       _TCB *rtcb = (_TCB*)g_readytorun.head;
       boolean switch_needed;
@@ -109,6 +122,9 @@ void up_reprioritize_rtr(_TCB *tcb, ubyte priority)
       /* Setup up the new task priority */
 
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority = (ubyte)priority;
+#endif
 
       /* Return the task to the specified blocked task list.
        * sched_addreadytorun will return TRUE if the task was
diff --git a/arch/pjrc-8051/src/up_reprioritizertr.c b/arch/pjrc-8051/src/up_reprioritizertr.c
index b148e755c5a..97d5682e086 100644
--- a/arch/pjrc-8051/src/up_reprioritizertr.c
+++ b/arch/pjrc-8051/src/up_reprioritizertr.c
@@ -1,7 +1,7 @@
-/************************************************************
+/****************************************************************************
  * up_reprioritizertr.c
  *
- *   Copyright (C) 2007 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -14,7 +14,7 @@
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
- * 3. Neither the name Gregory Nutt nor the names of its contributors may be
+ * 3. Neither the name NuttX nor the names of its contributors may be
  *    used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
@@ -31,11 +31,11 @@
  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  *
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Included Files
- ************************************************************/
+ ****************************************************************************/
 
 #include <nuttx/config.h>
 #include <sys/types.h>
@@ -45,23 +45,23 @@
 #include "os_internal.h"
 #include "up_internal.h"
 
-/************************************************************
+/****************************************************************************
  * Private Definitions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Data
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Funtions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Public Funtions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Name: up_reprioritize_rtr
  *
  * Description:
@@ -79,20 +79,33 @@
  *   tcb: The TCB of the task that has been reprioritized
  *   priority: The new task priority
  *
- ************************************************************/
+ ****************************************************************************/
 
 void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority)
 {
   /* Verify that the caller is sane */
 
-  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
-      tcb->task_state > LAST_READY_TO_RUN_STATE ||
-      priority < SCHED_PRIORITY_MIN || 
+#if CONFIG_DEBUG /* We only check parameters when debug is enabled */
+  if (priority < SCHED_PRIORITY_MIN || 
       priority > SCHED_PRIORITY_MAX)
     {
        PANIC(OSERR_BADREPRIORITIZESTATE);
     }
   else
+#endif
+  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
+           tcb->task_state > LAST_READY_TO_RUN_STATE)
+    {
+      /* This is a hack and needs to be fixed.. here some taks is reprioritizing
+       * another task that is not running.  Here we just set the priority of
+       * the task -- BUT some of the other states are also prioritized and the
+       * waiting task should also be re-ordered in the prioritized wiating list.
+       * As a consequence, the other task is still waiting at the lower priority.
+       */
+
+       tcb->sched_priority = priority;
+    }
+  else
     {
       FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
       boolean switch_needed;
@@ -109,6 +122,9 @@ void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority)
       /* Setup up the new task priority */
 
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority = (ubyte)priority;
+#endif
 
       /* Return the task to the specified blocked task list.
        * sched_addreadytorun will return TRUE if the task was
diff --git a/arch/sh/src/common/up_reprioritizertr.c b/arch/sh/src/common/up_reprioritizertr.c
index dccc6ad4a6f..58ba7a0d69a 100644
--- a/arch/sh/src/common/up_reprioritizertr.c
+++ b/arch/sh/src/common/up_reprioritizertr.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  *  arch/sh/src/common/up_reprioritizertr.c
  *
- *   Copyright (C) 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2008-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -85,14 +85,27 @@ void up_reprioritize_rtr(_TCB *tcb, ubyte priority)
 {
   /* Verify that the caller is sane */
 
-  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
-      tcb->task_state > LAST_READY_TO_RUN_STATE ||
-      priority < SCHED_PRIORITY_MIN || 
+#if CONFIG_DEBUG /* We only check parameters when debug is enabled */
+  if (priority < SCHED_PRIORITY_MIN || 
       priority > SCHED_PRIORITY_MAX)
     {
        PANIC(OSERR_BADREPRIORITIZESTATE);
     }
   else
+#endif
+  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
+           tcb->task_state > LAST_READY_TO_RUN_STATE)
+    {
+      /* This is a hack and needs to be fixed.. here some taks is reprioritizing
+       * another task that is not running.  Here we just set the priority of
+       * the task -- BUT some of the other states are also prioritized and the
+       * waiting task should also be re-ordered in the prioritized wiating list.
+       * As a consequence, the other task is still waiting at the lower priority.
+       */
+
+       tcb->sched_priority = priority;
+    }
+  else
     {
       _TCB *rtcb = (_TCB*)g_readytorun.head;
       boolean switch_needed;
@@ -109,6 +122,9 @@ void up_reprioritize_rtr(_TCB *tcb, ubyte priority)
       /* Setup up the new task priority */
 
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority = (ubyte)priority;
+#endif
 
       /* Return the task to the specified blocked task list.
        * sched_addreadytorun will return TRUE if the task was
diff --git a/arch/sim/src/up_reprioritizertr.c b/arch/sim/src/up_reprioritizertr.c
index 5f1d2a42cde..f68ff2a828a 100644
--- a/arch/sim/src/up_reprioritizertr.c
+++ b/arch/sim/src/up_reprioritizertr.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * up_reprioritizertr.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -85,14 +85,27 @@ void up_reprioritize_rtr(_TCB *tcb, ubyte priority)
 {
   /* Verify that the caller is sane */
 
-  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
-      tcb->task_state > LAST_READY_TO_RUN_STATE ||
-      priority < SCHED_PRIORITY_MIN || 
+#if CONFIG_DEBUG /* We only check parameters when debug is enabled */
+  if (priority < SCHED_PRIORITY_MIN || 
       priority > SCHED_PRIORITY_MAX)
     {
        PANIC(OSERR_BADREPRIORITIZESTATE);
     }
   else
+#endif
+  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
+           tcb->task_state > LAST_READY_TO_RUN_STATE)
+    {
+      /* This is a hack and needs to be fixed.. here some taks is reprioritizing
+       * another task that is not running.  Here we just set the priority of
+       * the task -- BUT some of the other states are also prioritized and the
+       * waiting task should also be re-ordered in the prioritized wiating list.
+       * As a consequence, the other task is still waiting at the lower priority.
+       */
+
+       tcb->sched_priority = priority;
+    }
+  else
     {
       _TCB *rtcb = (_TCB*)g_readytorun.head;
       boolean switch_needed;
@@ -109,6 +122,9 @@ void up_reprioritize_rtr(_TCB *tcb, ubyte priority)
       /* Setup up the new task priority */
 
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority = (ubyte)priority;
+#endif
 
       /* Return the task to the specified blocked task list.
        * sched_addreadytorun will return TRUE if the task was
diff --git a/arch/z16/src/common/up_reprioritizertr.c b/arch/z16/src/common/up_reprioritizertr.c
index e9c6a8a1e06..5692ac12c2d 100644
--- a/arch/z16/src/common/up_reprioritizertr.c
+++ b/arch/z16/src/common/up_reprioritizertr.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * common/up_reprioritizertr.c
  *
- *   Copyright (C) 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2008-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -89,14 +89,27 @@ void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority)
 {
   /* Verify that the caller is sane */
 
-  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
-      tcb->task_state > LAST_READY_TO_RUN_STATE ||
-      priority < SCHED_PRIORITY_MIN || 
+#if CONFIG_DEBUG /* We only check parameters when debug is enabled */
+  if (priority < SCHED_PRIORITY_MIN || 
       priority > SCHED_PRIORITY_MAX)
     {
        PANIC(OSERR_BADREPRIORITIZESTATE);
     }
   else
+#endif
+  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
+           tcb->task_state > LAST_READY_TO_RUN_STATE)
+    {
+      /* This is a hack and needs to be fixed.. here some taks is reprioritizing
+       * another task that is not running.  Here we just set the priority of
+       * the task -- BUT some of the other states are also prioritized and the
+       * waiting task should also be re-ordered in the prioritized wiating list.
+       * As a consequence, the other task is still waiting at the lower priority.
+       */
+
+       tcb->sched_priority = priority;
+    }
+  else
     {
       FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
       boolean switch_needed;
@@ -113,6 +126,9 @@ void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority)
       /* Setup up the new task priority */
 
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority = (ubyte)priority;
+#endif
 
       /* Return the task to the specified blocked task list.
        * sched_addreadytorun will return TRUE if the task was
diff --git a/arch/z80/src/common/up_reprioritizertr.c b/arch/z80/src/common/up_reprioritizertr.c
index 72e550d89b0..73272553e0f 100644
--- a/arch/z80/src/common/up_reprioritizertr.c
+++ b/arch/z80/src/common/up_reprioritizertr.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/z80/src/common/up_reprioritizertr.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -90,14 +90,27 @@ void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority)
 {
   /* Verify that the caller is sane */
 
-  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
-      tcb->task_state > LAST_READY_TO_RUN_STATE ||
-      priority < SCHED_PRIORITY_MIN || 
+#if CONFIG_DEBUG /* We only check parameters when debug is enabled */
+  if (priority < SCHED_PRIORITY_MIN || 
       priority > SCHED_PRIORITY_MAX)
     {
        PANIC(OSERR_BADREPRIORITIZESTATE);
     }
   else
+#endif
+  if (tcb->task_state < FIRST_READY_TO_RUN_STATE ||
+           tcb->task_state > LAST_READY_TO_RUN_STATE)
+    {
+      /* This is a hack and needs to be fixed.. here some taks is reprioritizing
+       * another task that is not running.  Here we just set the priority of
+       * the task -- BUT some of the other states are also prioritized and the
+       * waiting task should also be re-ordered in the prioritized wiating list.
+       * As a consequence, the other task is still waiting at the lower priority.
+       */
+
+       tcb->sched_priority = priority;
+    }
+  else
     {
       FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
       boolean switch_needed;
@@ -114,6 +127,9 @@ void up_reprioritize_rtr(FAR _TCB *tcb, ubyte priority)
       /* Setup up the new task priority */
 
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority = (ubyte)priority;
+#endif
 
       /* Return the task to the specified blocked task list.
        * sched_addreadytorun will return TRUE if the task was
diff --git a/configs/README.txt b/configs/README.txt
index e9b930cb1b6..cfd20b3b960 100644
--- a/configs/README.txt
+++ b/configs/README.txt
@@ -195,8 +195,10 @@ defconfig -- This is a configuration file similar to the Linux
 		CONFIG_JULIAN_TIME - Enables Julian time conversions
 		CONFIG_DEV_CONSOLE - Set if architecture-specific logic
 		  provides /dev/console.  Enables stdout, stderr, stdin.
-		CONFIG_MUTEX_TYPES - Set to enabled support for recursive and
+		CONFIG_MUTEX_TYPES - Set to enable support for recursive and
 		  errorcheck mutexes.  Enables pthread_mutexattr_settype().
+		CONFIG_PRIORITY_INHERITANCE - Set to enable support for
+		  priority inheritance on mutexes and semaphores.
 
 	The following can be used to disable categories of APIs supported
 	by the OS.  If the compiler supports weak functions, then it
diff --git a/configs/sim/ostest/defconfig b/configs/sim/ostest/defconfig
index 4ea688e85dc..f6e766dd5ba 100644
--- a/configs/sim/ostest/defconfig
+++ b/configs/sim/ostest/defconfig
@@ -1,7 +1,7 @@
 ############################################################################
 # configs/sim/ostest/defconfig
 #
-#   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -98,6 +98,7 @@ CONFIG_JULIAN_TIME=n
 CONFIG_DEV_CONSOLE=y
 CONFIG_DEV_LOWCONSOLE=n
 CONFIG_MUTEX_TYPES=y
+CONFIG_PRIORITY_INHERITANCE=n
 
 #
 # The following can be used to disable categories of
diff --git a/examples/ostest/Makefile b/examples/ostest/Makefile
index adb875932fa..d04de7bfec2 100644
--- a/examples/ostest/Makefile
+++ b/examples/ostest/Makefile
@@ -1,7 +1,7 @@
 ############################################################################
 # examples/ostest/Makefile
 #
-#   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -39,35 +39,47 @@
 ASRCS	= 
 AOBJS	= $(ASRCS:.S=$(OBJEXT))
 CSRCS	= main.c dev_null.c
+
 ifneq ($(CONFIG_DISABLE_PTHREAD),y)
 CSRCS	+= cancel.c cond.c mutex.c sem.c barrier.c
 ifneq ($(CONFIG_RR_INTERVAL),0)
 CSRCS	+= roundrobin.c
-endif
+endif # CONFIG_RR_INTERVAL
 ifeq ($(CONFIG_MUTEX_TYPES),y)
 CSRCS   += rmutex.c
-endif
-endif
+endif # CONFIG_MUTEX_TYPES
+endif # CONFIG_DISABLE_PTHREAD
+
 ifneq ($(CONFIG_DISABLE_SIGNALS),y)
 CSRCS	+= sighand.c
 ifneq ($(CONFIG_DISABLE_PTHREAD),y)
 ifneq ($(CONFIG_DISABLE_CLOCK),y)
 CSRCS	+= timedwait.c
-endif
-endif
-endif
+endif # CONFIG_DISABLE_CLOCK
+endif # CONFIG_DISABLE_PTHREAD
+endif # CONFIG_DISABLE_SIGNALS
+
 ifneq ($(CONFIG_DISABLE_MQUEUE),y)
 ifneq ($(CONFIG_DISABLE_PTHREAD),y)
 CSRCS	+= mqueue.c 
 ifneq ($(CONFIG_DISABLE_CLOCK),y)
 CSRCS	+= timedmqueue.c 
-endif
-endif
-endif
+endif # CONFIG_DISABLE_CLOCK
+endif # CONFIG_DISABLE_PTHREAD
+endif # CONFIG_DISABLE_MQUEUE
+
 ifneq ($(CONFIG_DISABLE_POSIX_TIMERS),y)
 CSRCS	+= posixtimer.c
 endif
 
+ifneq ($(CONFIG_DISABLE_SIGNALS),y)
+ifneq ($(CONFIG_DISABLE_PTHREAD),y)
+ifeq ($(CONFIG_PRIORITY_INHERITANCE),y)
+CSRCS	+= prioinherit.c
+endif # CONFIG_PRIORITY_INHERITANCE
+endif # CONFIG_DISABLE_PTHREAD
+endif # CONFIG_DISABLE_SIGNALS
+
 COBJS	= $(CSRCS:.c=$(OBJEXT))
 
 SRCS	= $(ASRCS) $(CSRCS)
diff --git a/examples/ostest/main.c b/examples/ostest/main.c
index 636d8af130a..a0c43416e4d 100644
--- a/examples/ostest/main.c
+++ b/examples/ostest/main.c
@@ -1,7 +1,7 @@
 /****************************************************************************
- * main.c
+ * ostest/main.c
  *
- *   Copyright (C) 2007, 2008, 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -382,6 +382,14 @@ static int user_main(int argc, char *argv[])
       check_test_memory_usage();
 #endif
 
+#if defined(CONFIG_PRIORITY_INHERITANCE) && !defined(CONFIG_DISABLE_SIGNALS) && !defined(CONFIG_DISABLE_PTHREAD)
+      /* Verify priority inheritance */
+
+      printf("\nuser_main: priority inheritance test\n");
+      priority_inheritance();
+      check_test_memory_usage();
+#endif /* CONFIG_PRIORITY_INHERITANCE && !CONFIG_DISABLE_SIGNALS && !CONFIG_DISABLE_PTHREAD */
+
       /* Compare memory usage at time user_start started until
        * user_main exits.  These should not be identical, but should
        * be similar enough that we can detect any serious OS memory
diff --git a/examples/ostest/ostest.h b/examples/ostest/ostest.h
index c94412cc134..8c71906c5f2 100644
--- a/examples/ostest/ostest.h
+++ b/examples/ostest/ostest.h
@@ -1,7 +1,7 @@
 /****************************************************************************
  * examples/ostest/ostest.h
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -135,4 +135,8 @@ extern void rr_test(void);
 
 extern void barrier_test(void);
 
+/* prioinherit.c ************************************************************/
+
+extern void priority_inheritance(void);
+
 #endif /* __OSTEST_H */
diff --git a/examples/ostest/prioinherit.c b/examples/ostest/prioinherit.c
new file mode 100644
index 00000000000..818f46b7528
--- /dev/null
+++ b/examples/ostest/prioinherit.c
@@ -0,0 +1,292 @@
+/****************************************************************************
+ * examples/ostest/prioinherit.c
+ *
+ *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * 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.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <sys/types.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <semaphore.h>
+#include <pthread.h>
+
+#include "ostest.h"
+
+#if defined(CONFIG_PRIORITY_INHERITANCE) && !defined(CONFIG_DISABLE_SIGNALS) && !defined(CONFIG_DISABLE_PTHREAD)
+
+/****************************************************************************
+ * Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+static sem_t g_sem;
+static volatile int g_middle = 0;
+
+/****************************************************************************
+ * Name: highpri_thread
+ ****************************************************************************/
+
+static void *highpri_thread(void *parameter)
+{
+  int ret;
+
+  printf("highpri_thread: Thread %d started\n");
+
+  ret = sem_wait(&g_sem);
+  if (ret != 0)
+    {
+      printf("highpri_thread: sem_take failed: %d\n", ret);
+    }
+  else if (g_middle == 1)
+    {
+      printf("highpri_thread: Success midpri_thread is still running!\n");
+    }
+  else
+    {
+      printf("highpri_thread: ERROR --  midpri_thread has already exited!\n");
+    }
+
+  sem_post(&g_sem);
+  printf("medpri_thread: Okay... I'm done!\n");
+  fflush(stdout);
+  return NULL;
+}
+
+/****************************************************************************
+ * Name: medpri_thread
+ ****************************************************************************/
+
+static void *medpri_thread(void *parameter)
+{
+  volatile long i;
+
+  printf("medpri_thread: Thread %d started ... I won't let go of the CPU!\n");
+  g_middle = 1;
+  for (i = 0; i < 0x7ffffff; i++);
+  printf("medpri_thread: Okay... I'm done!\n");
+  fflush(stdout);
+  return NULL;
+}
+
+/****************************************************************************
+ * Name: lowpri_thread
+ ****************************************************************************/
+
+static void *lowpri_thread(void *parameter)
+{
+  void *retval = (void*)-1;
+  int ret;
+
+  printf("lowpri_thread: Thread %d started\n");
+
+  ret = sem_wait(&g_sem);
+  if (ret != 0)
+    {
+      printf("lowpri_thread: sem_take failed: %d\n", ret);
+    }
+  else
+    {
+      /* Hang on to the thread until the middle priority thread runs */
+
+      while (g_middle == 0)
+        {
+          printf("lowpri_thread: Waiting for the midle pri task to run\n");
+          printf("lowpri_thread: I still have the semaphore\n");
+          sleep(1);
+        }
+
+      /* The middle priority task is running, let go of the semaphore */
+
+     if (g_middle == 1)
+       {
+         /* Good.. the middle priority task is still running but we got priority! */
+
+         retval = NULL;
+       }
+     else
+       {
+         printf("lowpri_thread: ERROR the middle priority task has already exitted!\n");
+       }
+    }
+
+  printf("lowpri_thread: Letting go of the semaphore\n");
+  sem_post(&g_sem);
+  printf("lowpri_thread: Okay... I'm done!\n");
+  fflush(stdout);
+  return retval;  
+}
+#endif /* CONFIG_PRIORITY_INHERITANCE && !CONFIG_DISABLE_SIGNALS && !CONFIG_DISABLE_PTHREAD */
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: priority_inheritance
+ ****************************************************************************/
+
+void priority_inheritance(void)
+{
+#if defined(CONFIG_PRIORITY_INHERITANCE) && !defined(CONFIG_DISABLE_SIGNALS) && !defined(CONFIG_DISABLE_PTHREAD)
+  pthread_t lowpri;
+  pthread_t medpri;
+  pthread_t highpri;
+  pthread_addr_t result;
+  pthread_attr_t attr;
+  struct sched_param sparam;
+  int my_pri;
+  int max_pri;
+  int mid_pri;
+  int min_pri;
+  int status;
+
+  printf("priority_inheritance: Started\n");
+
+  status = sched_getparam (getpid(), &sparam);
+  if (status != 0)
+    {
+      printf("priority_inheritance: sched_getparam failed\n");
+      sparam.sched_priority = PTHREAD_DEFAULT_PRIORITY;
+    }
+  my_pri  = sparam.sched_priority;
+
+  max_pri = sched_get_priority_max(SCHED_FIFO);
+  min_pri = sched_get_priority_min(SCHED_FIFO);
+  mid_pri = my_pri - 1;
+
+  sem_init(&g_sem, 0, 1);
+
+  /* Start the low priority task */
+
+  printf("priority_inheritance: Starting lowpri_thread at %d\n", min_pri);
+  status = pthread_attr_init(&attr);
+  if (status != 0)
+    {
+      printf("priority_inheritance: pthread_attr_init failed, status=%d\n", status);
+    }
+  sparam.sched_priority = min_pri;
+  status = pthread_attr_setschedparam(&attr,& sparam);
+  if (status != OK)
+    {
+      printf("priority_inheritance: pthread_attr_setschedparam failed, status=%d\n", status);
+    }
+  else
+    {
+      printf("priority_inheritance: Set lowpri_thread priority to %d\n", sparam.sched_priority);
+    }
+
+  status = pthread_create(&lowpri, &attr, lowpri_thread, NULL);
+  if (status != 0)
+    {
+      printf("priority_inheritance: pthread_create failed, status=%d\n", status);
+    }
+
+  printf("priority_inheritance: Waiting...\n");
+  sleep(5);
+
+  /* Start the medium priority task */
+
+  printf("priority_inheritance: Starting medpri_thread at %d\n", mid_pri);
+  status = pthread_attr_init(&attr);
+  if (status != 0)
+    {
+      printf("priority_inheritance: pthread_attr_init failed, status=%d\n", status);
+    }
+
+  sparam.sched_priority = mid_pri;
+  status = pthread_attr_setschedparam(&attr,& sparam);
+  if (status != OK)
+    {
+      printf("priority_inheritance: pthread_attr_setschedparam failed, status=%d\n", status);
+    }
+  else
+    {
+      printf("priority_inheritance: Set medpri_thread priority to %d\n", sparam.sched_priority);
+    }
+
+  status = pthread_create(&medpri, &attr, medpri_thread, NULL);
+  if (status != 0)
+    {
+      printf("priority_inheritance: pthread_create failed, status=%d\n", status);
+    }
+
+  /* Start the high priority task */
+
+  printf("priority_inheritance: Starting highpri_thread at %d\n", max_pri);
+  status = pthread_attr_init(&attr);
+  if (status != 0)
+    {
+      printf("priority_inheritance: pthread_attr_init failed, status=%d\n", status);
+    }
+
+  sparam.sched_priority = max_pri;
+  status = pthread_attr_setschedparam(&attr,& sparam);
+  if (status != OK)
+    {
+      printf("priority_inheritance: pthread_attr_setschedparam failed, status=%d\n", status);
+    }
+  else
+    {
+      printf("priority_inheritance: Set highpri_thread priority to %d\n", sparam.sched_priority);
+    }
+
+  status = pthread_create(&medpri, &attr, highpri_thread, NULL);
+  if (status != 0)
+    {
+      printf("priority_inheritance: pthread_create failed, status=%d\n", status);
+    }
+
+  /* Wait for all thread instances to complete */
+
+  printf("priority_inheritance: Waiting for highpri_thread to complete\n");
+  (void)pthread_join(highpri, &result);
+  printf("priority_inheritance: Waiting for medpri_thread to complete\n");
+  (void)pthread_join(medpri, &result);
+  printf("priority_inheritance: Waiting for lowpri_thread to complete\n");
+  (void)pthread_join(lowpri, &result);
+
+  printf("priority_inheritance: Finished\n");
+  sem_destroy(&g_sem);
+  fflush(stdout);
+#endif /* CONFIG_PRIORITY_INHERITANCE && !CONFIG_DISABLE_SIGNALS && !CONFIG_DISABLE_PTHREAD */
+}
diff --git a/include/nuttx/sched.h b/include/nuttx/sched.h
index 87cdc8127ea..500ae0c9736 100644
--- a/include/nuttx/sched.h
+++ b/include/nuttx/sched.h
@@ -1,7 +1,7 @@
 /********************************************************************************
  * nuttx/sched.h
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -177,6 +177,9 @@ struct _TCB
   entry_t  entry;                        /* Entry Point into the thread         */
   exitfunc_t exitfunc;                   /* Called if exit is called.           */
   ubyte    sched_priority;               /* Current priority of the thread      */
+#ifdef CONFIG_PRIORITY_INHERITANCE
+  ubyte    base_priority;                /* "Normal" priority of the thread     */
+#endif
   ubyte    task_state;                   /* Current state of the thread         */
   uint16   flags;                        /* Misc. general status flags          */
   sint16   lockcount;                    /* 0=preemptable (not-locked)          */
diff --git a/include/pthread.h b/include/pthread.h
index a6cccc7860c..44cd23c6a49 100644
--- a/include/pthread.h
+++ b/include/pthread.h
@@ -1,7 +1,7 @@
 /********************************************************************************
  * pthread.h
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -155,14 +155,14 @@ typedef pthread_addr_t  any_t;
 typedef pthread_addr_t (*pthread_startroutine_t)(pthread_addr_t);
 typedef pthread_startroutine_t  pthread_func_t;
 
-struct pthread_addr_s
+struct pthread_attr_s
 {
   size_t stacksize;    /* Size of the stack allocated for the pthead */
   sint16 priority;     /* Priority of the pthread */
   ubyte  policy;       /* Pthread scheduler policy */
   ubyte  inheritsched; /* Inherit parent prio/policy? */
 };
-typedef struct pthread_addr_s pthread_attr_t;
+typedef struct pthread_attr_s pthread_attr_t;
 
 typedef pid_t pthread_t;
 
diff --git a/include/semaphore.h b/include/semaphore.h
index bd2a24db125..5372d42126a 100644
--- a/include/semaphore.h
+++ b/include/semaphore.h
@@ -1,7 +1,7 @@
 /****************************************************************************
  * include/semaphore.h
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -64,6 +64,9 @@ struct sem_s
 {
   sint16 semcount;              /* >0 -> Num counts available */
                                 /* <0 -> Num tasks waiting for semaphore */
+#ifdef CONFIG_PRIORITY_INHERITANCE
+  void  *holder;                /* Holder TCB (actual type is _TCB) */
+#endif
 };
 typedef struct sem_s sem_t;
 
diff --git a/sched/os_internal.h b/sched/os_internal.h
index 665d05e743c..a9b1bfc856d 100644
--- a/sched/os_internal.h
+++ b/sched/os_internal.h
@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/os_internal.h
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
diff --git a/sched/pthread_create.c b/sched/pthread_create.c
index f13f76b146a..e515125738f 100644
--- a/sched/pthread_create.c
+++ b/sched/pthread_create.c
@@ -1,7 +1,7 @@
 /****************************************************************************
- * pthread_create.c
+ * sched/pthread_create.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -303,7 +303,7 @@ int pthread_create(FAR pthread_t *thread, FAR pthread_attr_t *attr,
 
   if (attr->inheritsched == PTHREAD_INHERIT_SCHED)
     {
-      /* Get the priority of this thread. */
+      /* Get the priority for this thread. */
 
       struct sched_param param;
       status = sched_getparam(0, &param);
diff --git a/sched/pthread_setschedprio.c b/sched/pthread_setschedprio.c
index d5a5705dcc3..6d3beb1de96 100644
--- a/sched/pthread_setschedprio.c
+++ b/sched/pthread_setschedprio.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * pthread_schedsetprio.c
  *
- *   Copyright (C) 2007 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -14,7 +14,7 @@
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
- * 3. Neither the name Gregory Nutt nor the names of its contributors may be
+ * 3. Neither the name NuttX nor the names of its contributors may be
  *    used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
diff --git a/sched/sched_setparam.c b/sched/sched_setparam.c
index e5a61c85686..20b0d68318e 100644
--- a/sched/sched_setparam.c
+++ b/sched/sched_setparam.c
@@ -1,7 +1,7 @@
-/************************************************************
- * sched_setparam.c
+/****************************************************************************
+ * sched/sched_setparam.c
  *
- *   Copyright (C) 2007 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -14,7 +14,7 @@
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
- * 3. Neither the name Gregory Nutt nor the names of its contributors may be
+ * 3. Neither the name NuttX nor the names of its contributors may be
  *    used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
@@ -31,11 +31,11 @@
  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  *
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Included Files
- ************************************************************/
+ ****************************************************************************/
 
 #include <nuttx/config.h>
 #include <sys/types.h>
@@ -44,35 +44,35 @@
 #include <nuttx/arch.h>
 #include "os_internal.h"
 
-/************************************************************
+/****************************************************************************
  * Definitions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Type Declarations
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Global Variables
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Variables
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Function Prototypes
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Functions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Public Functions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Name:  sched_setparam
  *
  * Description:
@@ -100,7 +100,7 @@
  *
  * Assumptions:
  *
- ************************************************************/
+ ****************************************************************************/
 
 int sched_setparam(pid_t pid, const struct sched_param *param)
 {
@@ -185,6 +185,9 @@ int sched_setparam(pid_t pid, const struct sched_param *param)
              /* Change the task priority */
 
              tcb->sched_priority = (ubyte)sched_priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+             tcb->base_priority  = (ubyte)sched_priority;
+#endif
            }
          break;
 
@@ -218,6 +221,9 @@ int sched_setparam(pid_t pid, const struct sched_param *param)
              /* Change the task priority */
 
              tcb->sched_priority = (ubyte)sched_priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+             tcb->base_priority  = (ubyte)sched_priority;
+#endif
 
              /* Put it back into the ready-to-run task list */
 
@@ -241,6 +247,9 @@ int sched_setparam(pid_t pid, const struct sched_param *param)
             /* Change the task priority */
 
             tcb->sched_priority = (ubyte)sched_priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+            tcb->base_priority  = (ubyte)sched_priority;
+#endif
 
             /* Put it back into the prioritized list at the correct
              * position
@@ -256,6 +265,9 @@ int sched_setparam(pid_t pid, const struct sched_param *param)
             /* Just change the task's priority */
 
             tcb->sched_priority = (ubyte)sched_priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+            tcb->base_priority  = (ubyte)sched_priority;
+#endif
           }
         break;
     }
diff --git a/sched/sem_destroy.c b/sched/sem_destroy.c
index 6dd60bc2839..66352230381 100644
--- a/sched/sem_destroy.c
+++ b/sched/sem_destroy.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/sem_destroy.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -103,7 +103,8 @@ int sem_destroy (FAR sem_t *sem)
     {
       /* There is really no particular action that we need
        * take to destroy a semaphore.  We will just reset
-       * the count to some reasonable value (1).
+       * the count to some reasonable value (1) and release
+       * ownership.
        *
        * Check if other threads are waiting on the semaphore.
        * In this case, the behavior is undefined.  We will:
@@ -114,6 +115,9 @@ int sem_destroy (FAR sem_t *sem)
         {
           sem->semcount = 1;
         }
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      sem->holder = NULL;
+#endif
       ret = OK;
     }
 
diff --git a/sched/sem_post.c b/sched/sem_post.c
index 186c3b87e18..ca20475989b 100644
--- a/sched/sem_post.c
+++ b/sched/sem_post.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/sem_post.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -104,6 +104,9 @@
 
 int sem_post(FAR sem_t *sem)
 {
+#ifdef CONFIG_PRIORITY_INHERITANCE
+  FAR _TCB  *rtcb = (FAR _TCB*)g_readytorun.head;
+#endif
   FAR _TCB  *stcb;
   STATUS     ret = ERROR;
   irqstate_t saved_state;
@@ -122,6 +125,9 @@ int sem_post(FAR sem_t *sem)
       /* Perform the semaphore unlock operation. */
 
       ASSERT(sem->semcount < SEM_VALUE_MAX);
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      sem->holder = NULL;
+#endif
       sem->semcount++;
 
       /* If the result of of semaphore unlock is non-positive, then
@@ -151,6 +157,18 @@ int sem_post(FAR sem_t *sem)
               up_unblock_task(stcb);
             }
         }
+
+      /* Check if we need to drop our priority.  Our priority could have
+       * been boosted while we held the semaphore.
+       */
+
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      if (rtcb->sched_priority != rtcb->base_priority)
+        {
+           up_reprioritize_rtr(rtcb, rtcb->base_priority);
+        }
+#endif
+
       ret = OK;
 
       /* Interrupts may now be enabled. */
diff --git a/sched/sem_wait.c b/sched/sem_wait.c
index ba223b1d4b4..d0735d76e27 100644
--- a/sched/sem_wait.c
+++ b/sched/sem_wait.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/sem_wait.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -98,6 +98,9 @@
 int sem_wait(FAR sem_t *sem)
 {
   FAR _TCB  *rtcb = (FAR _TCB*)g_readytorun.head;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+  FAR _TCB  *htcb;
+#endif
   int        ret = ERROR;
   irqstate_t saved_state;
 
@@ -125,6 +128,9 @@ int sem_wait(FAR sem_t *sem)
           /* It is, let the task take the semaphore. */
 
           sem->semcount--;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+          sem->holder = rtcb;
+#endif
           rtcb->waitsem = NULL;
           ret = OK;
         }
@@ -144,7 +150,7 @@ int sem_wait(FAR sem_t *sem)
               PANIC(OSERR_BADWAITSEM);
             }
 
-          /* Handle the POSIX semaphore */
+          /* Handle the POSIX semaphore (but don't set the owner yet) */
 
           sem->semcount--;
 
@@ -152,11 +158,36 @@ int sem_wait(FAR sem_t *sem)
 
           rtcb->waitsem = sem;
 
+          /* If priority inheritance is enabled, then check the priority of
+           * the holder of the semaphore.
+           */
+
+#ifdef CONFIG_PRIORITY_INHERITANCE
+          /* Disable context switching.  The following operations must be
+           * atomic with regard to the scheduler.
+           */
+
+          sched_lock();
+          htcb = sem->holder;
+          if (htcb && htcb->sched_priority < rtcb->sched_priority)
+            {
+              /* Raise the priority of the holder of the semaphore.  This
+               * cannot cause a context switch because we have preemption
+               * disabled.  The task will be marked "pending" and the switch
+               * will occur during up_block_task() processing.
+               */
+               
+              up_reprioritize_rtr(htcb, rtcb->sched_priority);
+            }
+#endif
           /* Add the TCB to the prioritized semaphore wait queue */
 
           *get_errno_ptr() = 0;
           up_block_task(rtcb, TSTATE_WAIT_SEM);
 
+#ifdef CONFIG_PRIORITY_INHERITANCE
+          sched_unlock();
+#endif
           /* When we resume at this point, either (1) the semaphore has been
            * assigned to this thread of execution, or (2) the semaphore wait
            * has been interrupted by a signal.  We can detect the latter case
@@ -165,6 +196,11 @@ int sem_wait(FAR sem_t *sem)
 
           if (*get_errno_ptr() != EINTR)
             {
+              /* We hold the semaphore */
+
+#ifdef CONFIG_PRIORITY_INHERITANCE
+              sem->holder = rtcb;
+#endif
               ret = OK;
             }
           else
diff --git a/sched/task_restart.c b/sched/task_restart.c
index 3d682eb3d99..c254dd3039e 100644
--- a/sched/task_restart.c
+++ b/sched/task_restart.c
@@ -1,7 +1,7 @@
-/************************************************************
- * task_restart.c
+/****************************************************************************
+ * sched/task_restart.c
  *
- *   Copyright (C) 2007 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -14,7 +14,7 @@
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
- * 3. Neither the name Gregory Nutt nor the names of its contributors may be
+ * 3. Neither the name NuttX nor the names of its contributors may be
  *    used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
@@ -31,11 +31,11 @@
  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  *
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Included Files
- ************************************************************/
+ ****************************************************************************/
 
 #include <nuttx/config.h>
 #include <sys/types.h>
@@ -44,35 +44,35 @@
 #include "os_internal.h"
 #include "sig_internal.h"
 
-/************************************************************
+/****************************************************************************
  * Definitions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Type Declarations
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Global Variables
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Variables
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Function Prototypes
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Private Functions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Public Functions
- ************************************************************/
+ ****************************************************************************/
 
-/************************************************************
+/****************************************************************************
  * Name: task_restart
  *
  * Description:
@@ -94,7 +94,7 @@
  *   (2) The pid is not associated with any task known to
  *       the system.
  *
- ************************************************************/
+ ****************************************************************************/
 
 STATUS task_restart(pid_t pid)
 {
@@ -149,6 +149,9 @@ STATUS task_restart(pid_t pid)
        /* Reset the task priority  */
 
        tcb->sched_priority = tcb->init_priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+       tcb->base_priority  = tcb->init_priority;
+#endif
 
        /* Re-initialize the processor-specific portion of the TCB
         * This will reset the entry point and the start-up parameters
diff --git a/sched/task_setup.c b/sched/task_setup.c
index 6b80d5db05b..25a85394a9a 100644
--- a/sched/task_setup.c
+++ b/sched/task_setup.c
@@ -1,7 +1,7 @@
 /****************************************************************************
- * task_setup.c
+ * sched/task_setup.c
  *
- *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -184,6 +184,9 @@ STATUS task_schedsetup(FAR _TCB *tcb, int priority,
 
       tcb->init_priority  = (ubyte)priority;
       tcb->sched_priority = (ubyte)priority;
+#ifdef CONFIG_PRIORITY_INHERITANCE
+      tcb->base_priority  = (ubyte)priority;
+#endif
       tcb->start          = start;
       tcb->entry.main     = main;