current_regs should be volatile; add support for nested interrupts; enable interrupts during syscall processing

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3475 42af7a65-404d-4744-a932-0658087f49c3

24 files changed, 152 insertions, 54 deletions

diff --git a/nuttx/arch/arm/include/cortexm3/irq.h b/nuttx/arch/arm/include/cortexm3/irq.h
index 5c9ef04c0..063568655 100644
--- a/nuttx/arch/arm/include/cortexm3/irq.h
+++ b/nuttx/arch/arm/include/cortexm3/irq.h
@@ -156,6 +156,13 @@ struct xcptcontext
 
 #ifndef __ASSEMBLY__
 
+/* Disable IRQs */
+
+static inline void irqdisable(void)
+{
+  __asm__ __volatile__ ("\tcpsid  i\n");
+}
+
 /* Save the current primask state & disable IRQs */
 
 static inline irqstate_t irqsave(void)
@@ -176,6 +183,13 @@ static inline irqstate_t irqsave(void)
   return primask;
 }
 
+/* Enable IRQs */
+
+static inline void irqenable(void)
+{
+  __asm__ __volatile__ ("\tcpsie  i\n");
+}
+
 /* Restore saved primask state */
 
 static inline void irqrestore(irqstate_t primask)
diff --git a/nuttx/arch/arm/src/arm/up_dataabort.c b/nuttx/arch/arm/src/arm/up_dataabort.c
index 05886e384..c36970c1b 100644
--- a/nuttx/arch/arm/src/arm/up_dataabort.c
+++ b/nuttx/arch/arm/src/arm/up_dataabort.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/arm/src/arm/up_dataabort.c
  *
- *   Copyright (C) 2007-2010 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -103,13 +103,19 @@
 void up_dataabort(uint32_t *regs, uint32_t far, uint32_t fsr)
 {
   FAR _TCB *tcb = (FAR _TCB *)g_readytorun.head;
+#ifdef CONFIG_PAGING
+   uint32_t *savestate;
 
   /* Save the saved processor context in current_regs where it can be accessed
    * for register dumps and possibly context switching.
    */
 
+
+  savestate    = (uint32_t*)current_regs;
+#endif
   current_regs = regs;
 
+#ifdef CONFIG_PAGING
   /* In the NuttX on-demand paging implementation, only the read-only, .text
    * section is paged.  However, the ARM compiler generated PC-relative data
    * fetches from within the .text sections.  Also, it is customary to locate
@@ -162,12 +168,16 @@ void up_dataabort(uint32_t *regs, uint32_t far, uint32_t fsr)
 
   pg_miss();
 
-  /* Indicate that we are no longer in an interrupt handler */
+  /* Restore the previous value of current_regs.  NULL would indicate that
+   * we are no longer in an interrupt handler.  It will be non-NULL if we
+   * are returning from a nested interrupt.
+   */
 
-  current_regs = NULL;
+  current_regs = savestate;
   return;
 
 segfault:
+#endif
   lldbg("Data abort. PC: %08x FAR: %08x FSR: %08x\n", regs[REG_PC], far, fsr);
   PANIC(OSERR_ERREXCEPTION);
 }
diff --git a/nuttx/arch/arm/src/arm/up_doirq.c b/nuttx/arch/arm/src/arm/up_doirq.c
index 5c127b75c..1f1c77473 100644
--- a/nuttx/arch/arm/src/arm/up_doirq.c
+++ b/nuttx/arch/arm/src/arm/up_doirq.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/arm/src/arm/up_doirq.c
  *
- *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -76,6 +76,8 @@ void up_doirq(int irq, uint32_t *regs)
 #ifdef CONFIG_SUPPRESS_INTERRUPTS
   PANIC(OSERR_ERREXCEPTION);
 #else
+  uint32_t *savestate;
+
   /* Nested interrupts are not supported in this implementation.  If you want
    * implemented nested interrupts, you would have to (1) change the way that
    * current regs is handled and (2) the design associated with
@@ -86,7 +88,7 @@ void up_doirq(int irq, uint32_t *regs)
    * current_regs is also used to manage interrupt level context switches.
    */
 
-  DEBUGASSERT(current_regs == NULL);
+  savestate    = (uint32_t*)current_regs;
   current_regs = regs;
 
   /* Mask and acknowledge the interrupt */
@@ -97,9 +99,12 @@ void up_doirq(int irq, uint32_t *regs)
 
   irq_dispatch(irq, regs);
 
-  /* Indicate that we are no long in an interrupt handler */
+  /* Restore the previous value of current_regs.  NULL would indicate that
+   * we are no longer in an interrupt handler.  It will be non-NULL if we
+   * are returning from a nested interrupt.
+   */
 
-  current_regs = NULL;
+  current_regs = savestate;
 
   /* Unmask the last interrupt (global interrupts are still disabled) */
 
diff --git a/nuttx/arch/arm/src/arm/up_prefetchabort.c b/nuttx/arch/arm/src/arm/up_prefetchabort.c
index 2d184bad6..ed3dd91d3 100644
--- a/nuttx/arch/arm/src/arm/up_prefetchabort.c
+++ b/nuttx/arch/arm/src/arm/up_prefetchabort.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  *  arch/arm/src/src/up_prefetchabort.c
  *
- *   Copyright (C) 2007-2010 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -89,10 +89,15 @@
 
 void up_prefetchabort(uint32_t *regs)
 {
+#ifdef CONFIG_PAGING
+   uint32_t *savestate;
+
   /* Save the saved processor context in current_regs where it can be accessed
    * for register dumps and possibly context switching.
    */
 
+  savestate    = (uint32_t*)current_regs;
+#endif
   current_regs = regs;
 
 #ifdef CONFIG_PAGING
@@ -133,9 +138,12 @@ void up_prefetchabort(uint32_t *regs)
 
       pg_miss();
 
-      /* Indicate that we are no longer in an interrupt handler */
+      /* Restore the previous value of current_regs.  NULL would indicate that
+       * we are no longer in an interrupt handler.  It will be non-NULL if we
+       * are returning from a nested interrupt.
+       */
 
-      current_regs = NULL;
+      current_regs = savestate;
     }
   else
 #endif
diff --git a/nuttx/arch/arm/src/c5471/c5471_irq.c b/nuttx/arch/arm/src/c5471/c5471_irq.c
index 6906e8f8d..fbeb2e720 100644
--- a/nuttx/arch/arm/src/c5471/c5471_irq.c
+++ b/nuttx/arch/arm/src/c5471/c5471_irq.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/arm/src/c5471/c5471_irq.c
  *
- *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -59,7 +59,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/common/up_internal.h b/nuttx/arch/arm/src/common/up_internal.h
index 9fe4464c7..803a6563d 100644
--- a/nuttx/arch/arm/src/common/up_internal.h
+++ b/nuttx/arch/arm/src/common/up_internal.h
@@ -82,11 +82,11 @@
  */
 
 #ifdef CONFIG_ARCH_CORTEXM3
-#  define up_savestate(regs)    up_copystate(regs, current_regs)
+#  define up_savestate(regs)    up_copystate(regs, (uint32_t*)current_regs)
 #  define up_restorestate(regs) (current_regs = regs)
 #else
-#  define up_savestate(regs)    up_copystate(regs, current_regs)
-#  define up_restorestate(regs) up_copystate(current_regs, regs)
+#  define up_savestate(regs)    up_copystate(regs, (uint32_t*)current_regs)
+#  define up_restorestate(regs) up_copystate((uint32_t*)current_regs, regs)
 #endif
 
 /****************************************************************************
@@ -107,7 +107,7 @@ typedef void (*up_vector_t)(void);
  * interrupt processing.
  */
 
-extern uint32_t *current_regs;
+extern volatile uint32_t *current_regs;
 
 /* This is the beginning of heap as provided from up_head.S.
  * This is the first address in DRAM after the loaded
diff --git a/nuttx/arch/arm/src/cortexm3/up_doirq.c b/nuttx/arch/arm/src/cortexm3/up_doirq.c
index d5f3a6185..fc2f75c97 100644
--- a/nuttx/arch/arm/src/cortexm3/up_doirq.c
+++ b/nuttx/arch/arm/src/cortexm3/up_doirq.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/arm/src/cortexm3/up_doirq.c
  *
- *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -76,6 +76,8 @@ uint32_t *up_doirq(int irq, uint32_t *regs)
 #ifdef CONFIG_SUPPRESS_INTERRUPTS
   PANIC(OSERR_ERREXCEPTION);
 #else
+  uint32_t *savestate;
+
   /* Nested interrupts are not supported in this implementation.  If you want
    * implemented nested interrupts, you would have to (1) change the way that
    * current regs is handled and (2) the design associated with
@@ -86,7 +88,7 @@ uint32_t *up_doirq(int irq, uint32_t *regs)
    * current_regs is also used to manage interrupt level context switches.
    */
 
-  DEBUGASSERT(current_regs == NULL);
+  savestate     = (uint32_t*)current_regs;
   current_regs = regs;
 
   /* Mask and acknowledge the interrupt */
@@ -103,11 +105,14 @@ uint32_t *up_doirq(int irq, uint32_t *regs)
    * switch occurred during interrupt processing.
    */
 
-  regs = current_regs;
+  regs = (uint32_t*)current_regs;
 
-  /* Indicate that we are no long in an interrupt handler */
+  /* Restore the previous value of current_regs.  NULL would indicate that
+   * we are no longer in an interrupt handler.  It will be non-NULL if we
+   * are returning from a nested interrupt.
+   */
 
-  current_regs = NULL;
+  current_regs = savestate;
 
   /* Unmask the last interrupt (global interrupts are still disabled) */
 
diff --git a/nuttx/arch/arm/src/cortexm3/up_svcall.c b/nuttx/arch/arm/src/cortexm3/up_svcall.c
index ec67617a7..f7e55a98b 100644
--- a/nuttx/arch/arm/src/cortexm3/up_svcall.c
+++ b/nuttx/arch/arm/src/cortexm3/up_svcall.c
@@ -57,7 +57,20 @@
 /****************************************************************************
  * Pre-processor Definitions
  ****************************************************************************/
+/* Configuration ************************************************************/
+
+#undef SYSCALL_INTERRUPTIBLE
+#if defined(CONFIG_NUTTX_KERNEL)
+#  if CONFIG_ARCH_INTERRUPTSTACK > 3
+#    warning "CONFIG_ARCH_INTERRUPTSTACK and CONFIG_NUTTX_KERNEL are incompatible"
+#    warning "options as currently implemented.  Interrupts will have to be disabled"
+#    warning "during SYScall processing to avoid un-handled nested interrupts"
+#  else
+#    define SYSCALL_INTERRUPTIBLE 1
+#  endif
+#endif
 
+/* Debug ********************************************************************/
 /* Debug output from this file may interfere with context switching!  To get
  * debug output you must enabled the following in your NuttX configuration:
  *
@@ -116,6 +129,12 @@ static inline void dispatch_syscall(uint32_t *regs)
 
       int index = cmd - CONFIG_SYS_RESERVED;
 
+      /* Enable interrupts while the SYSCALL executes */
+
+#ifdef SYSCALL_INTERRUPTIBLE
+      irqenable();
+#endif
+
       /* Call the correct stub for each SYS call, based on the number of parameters */
 
       svcdbg("Calling stub%d at %p\n", index, g_stubloopkup[index].stub0);
@@ -177,6 +196,10 @@ static inline void dispatch_syscall(uint32_t *regs)
                  cmd, g_stubnparms[index]);
           break;
         }
+
+#ifdef SYSCALL_INTERRUPTIBLE
+      irqdisable();
+#endif
     }
 
   /* Set up the return vaue.  First, check if a context switch occurred. 
diff --git a/nuttx/arch/arm/src/dm320/dm320_decodeirq.c b/nuttx/arch/arm/src/dm320/dm320_decodeirq.c
index a844fcae9..cb3efa5b9 100644
--- a/nuttx/arch/arm/src/dm320/dm320_decodeirq.c
+++ b/nuttx/arch/arm/src/dm320/dm320_decodeirq.c
@@ -2,7 +2,7 @@
  * arch/arm/src/dm320/dm320_decodeirq.c
  * arch/arm/src/chip/dm320_decodeirq.c
  *
- *   Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -94,6 +94,8 @@ void up_decodeirq(uint32_t* regs)
 
       if ((unsigned)irq < NR_IRQS)
         {
+          uint32_t *savestate;
+
           /* Mask and acknowledge the interrupt */
 
           up_maskack_irq(irq);
@@ -102,15 +104,19 @@ void up_decodeirq(uint32_t* regs)
            * current_regs is also used to manage interrupt level context switches.
            */
 
+          savestate    = (uint32_t*)current_regs;
           current_regs = regs;
 
           /* Deliver the IRQ */
 
           irq_dispatch(irq, regs);
 
-          /* Indicate that we are no longer in an interrupt handler */
+          /* Restore the previous value of current_regs.  NULL would indicate that
+           * we are no longer in an interrupt handler.  It will be non-NULL if we
+           * are returning from a nested interrupt.
+           */
 
-          current_regs = NULL;
+          current_regs = savestate;
 
           /* Unmask the last interrupt (global interrupts are still
            * disabled).
diff --git a/nuttx/arch/arm/src/dm320/dm320_irq.c b/nuttx/arch/arm/src/dm320/dm320_irq.c
index f094bab1c..eb8201bb4 100644
--- a/nuttx/arch/arm/src/dm320/dm320_irq.c
+++ b/nuttx/arch/arm/src/dm320/dm320_irq.c
@@ -57,7 +57,7 @@
  * Public Data
  ************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/imx/imx_decodeirq.c b/nuttx/arch/arm/src/imx/imx_decodeirq.c
index 96a40fd4a..55c72ed76 100644
--- a/nuttx/arch/arm/src/imx/imx_decodeirq.c
+++ b/nuttx/arch/arm/src/imx/imx_decodeirq.c
@@ -2,7 +2,7 @@
  * arch/arm/src/imx/imx_decodeirq.c
  * arch/arm/src/chip/imx_decodeirq.c
  *
- *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -78,6 +78,7 @@ void up_decodeirq(uint32_t* regs)
   current_regs = regs;
   PANIC(OSERR_ERREXCEPTION);
 #else
+  uint32_t* savestate;
   uint32_t regval;
   int irq;
 
@@ -85,6 +86,7 @@ void up_decodeirq(uint32_t* regs)
    * current_regs is also used to manage interrupt level context switches.
    */
 
+  savestate    = (uint32_t*)current_regs;
   current_regs = regs;
 
   /* Loop while there are pending interrupts to be processed */
@@ -124,8 +126,11 @@ void up_decodeirq(uint32_t* regs)
     }
   while (irq < NR_IRQS);
 
-  /* Indicate that we are no longer in an interrupt handler */
+  /* Restore the previous value of current_regs.  NULL would indicate that
+   * we are no longer in an interrupt handler.  It will be non-NULL if we
+   * are returning from a nested interrupt.
+   */
 
-  current_regs = NULL;
+  current_regs = savestate;
 #endif
 }
diff --git a/nuttx/arch/arm/src/imx/imx_irq.c b/nuttx/arch/arm/src/imx/imx_irq.c
index b346064c5..934a60f0b 100644
--- a/nuttx/arch/arm/src/imx/imx_irq.c
+++ b/nuttx/arch/arm/src/imx/imx_irq.c
@@ -2,7 +2,7 @@
  * arch/arm/src/imc/imx_irq.c
  * arch/arm/src/chip/imx_irq.c
  *
- *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -56,7 +56,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/lm3s/lm3s_irq.c b/nuttx/arch/arm/src/lm3s/lm3s_irq.c
index da7f3d9c3..915ce3d13 100644
--- a/nuttx/arch/arm/src/lm3s/lm3s_irq.c
+++ b/nuttx/arch/arm/src/lm3s/lm3s_irq.c
@@ -75,7 +75,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/lpc17xx/lpc17_irq.c b/nuttx/arch/arm/src/lpc17xx/lpc17_irq.c
index 967de45d7..cf3467833 100755
--- a/nuttx/arch/arm/src/lpc17xx/lpc17_irq.c
+++ b/nuttx/arch/arm/src/lpc17xx/lpc17_irq.c
@@ -75,7 +75,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/lpc214x/lpc214x_decodeirq.c b/nuttx/arch/arm/src/lpc214x/lpc214x_decodeirq.c
index dc76509a9..6317066c3 100644
--- a/nuttx/arch/arm/src/lpc214x/lpc214x_decodeirq.c
+++ b/nuttx/arch/arm/src/lpc214x/lpc214x_decodeirq.c
@@ -1,7 +1,7 @@
 /********************************************************************************
  * arch/arm/src/lpc214x/lpc214x_decodeirq.c
  *
- *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -145,19 +145,25 @@ static void lpc214x_decodeirq( uint32_t *regs)
 
   if (irq < NR_IRQS)
     {
+      uint32_t *savestate;
+
       /* Current regs non-zero indicates that we are processing an interrupt;
        * current_regs is also used to manage interrupt level context switches.
        */
 
+      savestate    = (uint32_t*)current_regs;
       current_regs = regs;
 
       /* Deliver the IRQ */
 
       irq_dispatch(irq, regs);
 
-      /* Indicate that we are no long in an interrupt handler */
+      /* Restore the previous value of current_regs.  NULL would indicate that
+       * we are no longer in an interrupt handler.  It will be non-NULL if we
+       * are returning from a nested interrupt.
+       */
 
-      current_regs = NULL;
+      current_regs = savestate;
     }
 #endif
 }
diff --git a/nuttx/arch/arm/src/lpc214x/lpc214x_irq.c b/nuttx/arch/arm/src/lpc214x/lpc214x_irq.c
index 9d8ed817b..a8b91037c 100644
--- a/nuttx/arch/arm/src/lpc214x/lpc214x_irq.c
+++ b/nuttx/arch/arm/src/lpc214x/lpc214x_irq.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/arm/src/lpc214x/lpc214x_irq.c
  *
- *   Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -59,7 +59,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/lpc2378/lpc23xx_decodeirq.c b/nuttx/arch/arm/src/lpc2378/lpc23xx_decodeirq.c
index 42b678432..100502a22 100755
--- a/nuttx/arch/arm/src/lpc2378/lpc23xx_decodeirq.c
+++ b/nuttx/arch/arm/src/lpc2378/lpc23xx_decodeirq.c
@@ -6,7 +6,7 @@
  *
  * This file is part of the NuttX RTOS and based on the lpc2148 port:
  *
- *   Copyright (C) 2010 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2010, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -131,11 +131,13 @@ static void lpc23xx_decodeirq(uint32_t *regs)
 
   if (irq < NR_IRQS)            /* redundant check ?? */
     {
+       uint32_t *savestate;
+
       /* Current regs non-zero indicates that we are processing an interrupt;
        * current_regs is also used to manage interrupt level context switches.
        */
 
-      DEBUGASSERT(current_regs == NULL);
+      savestate    = (uint32_t*)current_regs;
       current_regs = regs;
 
       /* Mask and acknowledge the interrupt */
@@ -146,9 +148,12 @@ static void lpc23xx_decodeirq(uint32_t *regs)
 
       irq_dispatch(irq, regs);
 
-      /* Indicate that we are no longer in an interrupt handler */
+      /* Restore the previous value of current_regs.  NULL would indicate that
+       * we are no longer in an interrupt handler.  It will be non-NULL if we
+       * are returning from a nested interrupt.
+       */
 
-      current_regs = NULL;
+      current_regs = savestate;
     }
 
 #endif
diff --git a/nuttx/arch/arm/src/lpc2378/lpc23xx_irq.c b/nuttx/arch/arm/src/lpc2378/lpc23xx_irq.c
index 9a6268a2f..10f188cba 100755
--- a/nuttx/arch/arm/src/lpc2378/lpc23xx_irq.c
+++ b/nuttx/arch/arm/src/lpc2378/lpc23xx_irq.c
@@ -65,7 +65,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/lpc313x/lpc313x_decodeirq.c b/nuttx/arch/arm/src/lpc313x/lpc313x_decodeirq.c
index 9abaff3c1..119e65c50 100755
--- a/nuttx/arch/arm/src/lpc313x/lpc313x_decodeirq.c
+++ b/nuttx/arch/arm/src/lpc313x/lpc313x_decodeirq.c
@@ -102,6 +102,8 @@ void up_decodeirq(uint32_t *regs)
 
       if ((unsigned)irq < NR_IRQS)
         {
+          uint32_t* savestate;
+
           /* Mask and acknowledge the interrupt */
 
           up_maskack_irq(irq);
@@ -110,15 +112,19 @@ void up_decodeirq(uint32_t *regs)
            * current_regs is also used to manage interrupt level context switches.
            */
 
+          savestate    = (uint32_t*)current_regs;
           current_regs = regs;
 
           /* Deliver the IRQ */
 
           irq_dispatch(irq, regs);
 
-          /* Indicate that we are no longer in an interrupt handler */
+          /* Restore the previous value of current_regs.  NULL would indicate that
+           * we are no longer in an interrupt handler.  It will be non-NULL if we
+           * are returning from a nested interrupt.
+           */
 
-          current_regs = NULL;
+          current_regs = savestate;
 
           /* Unmask the last interrupt (global interrupts are still
            * disabled).
diff --git a/nuttx/arch/arm/src/lpc313x/lpc313x_irq.c b/nuttx/arch/arm/src/lpc313x/lpc313x_irq.c
index 35ef3e89e..9b7f10e12 100755
--- a/nuttx/arch/arm/src/lpc313x/lpc313x_irq.c
+++ b/nuttx/arch/arm/src/lpc313x/lpc313x_irq.c
@@ -2,7 +2,7 @@
  * arch/arm/src/lpc313x/lpc313x_irq.c
  * arch/arm/src/chip/lpc313x_irq.c
  *
- *   Copyright (C) 2009-2010 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2009-2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -64,7 +64,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/sam3u/sam3u_irq.c b/nuttx/arch/arm/src/sam3u/sam3u_irq.c
index 1d19c126e..228be0f1f 100755
--- a/nuttx/arch/arm/src/sam3u/sam3u_irq.c
+++ b/nuttx/arch/arm/src/sam3u/sam3u_irq.c
@@ -75,7 +75,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/stm32/stm32_irq.c b/nuttx/arch/arm/src/stm32/stm32_irq.c
index 7f963a117..b27f5448e 100644
--- a/nuttx/arch/arm/src/stm32/stm32_irq.c
+++ b/nuttx/arch/arm/src/stm32/stm32_irq.c
@@ -75,7 +75,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data
diff --git a/nuttx/arch/arm/src/str71x/str71x_decodeirq.c b/nuttx/arch/arm/src/str71x/str71x_decodeirq.c
index 4182ab417..8a24ea44d 100644
--- a/nuttx/arch/arm/src/str71x/str71x_decodeirq.c
+++ b/nuttx/arch/arm/src/str71x/str71x_decodeirq.c
@@ -1,7 +1,7 @@
 /********************************************************************************
  * arch/arm/src/str71x/str71x_decodeirq.c
  *
- *   Copyright (C) 2008-2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2008-2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -108,11 +108,13 @@ void up_decodeirq(uint32_t *regs)
 
   if (irq < NR_IRQS)
     {
+      uint32_t* savestate;
+
       /* Current regs non-zero indicates that we are processing an interrupt;
        * current_regs is also used to manage interrupt level context switches.
        */
 
-      DEBUGASSERT(current_regs == NULL);
+      savestate     = (uint32_t*)current_regs;
       current_regs = regs;
 
       /* Mask and acknowledge the interrupt */
@@ -123,9 +125,12 @@ void up_decodeirq(uint32_t *regs)
 
       irq_dispatch(irq, regs);
 
-      /* Indicate that we are no long in an interrupt handler */
+      /* Restore the previous value of current_regs.  NULL would indicate that
+       * we are no longer in an interrupt handler.  It will be non-NULL if we
+       * are returning from a nested interrupt.
+       */
 
-      current_regs = NULL;
+      current_regs = savestate;
 
       /* Unmask the last interrupt (global interrupts are still disabled) */
 
diff --git a/nuttx/arch/arm/src/str71x/str71x_irq.c b/nuttx/arch/arm/src/str71x/str71x_irq.c
index d27412e17..c5c359cdf 100644
--- a/nuttx/arch/arm/src/str71x/str71x_irq.c
+++ b/nuttx/arch/arm/src/str71x/str71x_irq.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/arm/src/st71x/st71x_irq.c
  *
- *   Copyright (C) 2008-2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2008-2009, 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -58,7 +58,7 @@
  * Public Data
  ****************************************************************************/
 
-uint32_t *current_regs;
+volatile uint32_t *current_regs;
 
 /****************************************************************************
  * Private Data