Completes port of interrpt handling logic

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3340 42af7a65-404d-4744-a932-0658087f49c3

19 files changed, 939 insertions, 136 deletions

diff --git a/nuttx/arch/x86/include/i486/arch.h b/nuttx/arch/x86/include/i486/arch.h
index f2c270067..e2dde5555 100755
--- a/nuttx/arch/x86/include/i486/arch.h
+++ b/nuttx/arch/x86/include/i486/arch.h
@@ -85,7 +85,7 @@
  * Public Types
  ****************************************************************************/
 
-/* GDT data structures
+/* GDT data structures ******************************************************
  *
  * The Global Descriptor Table or GDT is a data structure used by Intel x86-
  * family processors starting with the 80286 in order to define the
@@ -114,7 +114,33 @@ struct gdt_entry_s
 struct gdt_ptr_s
 {
   uint16_t limit;               /* The upper 16 bits of all selector limits */
-  uint32_t base;                /* The address of the first gdt_entry_t struct */
+  uint32_t base;                /* The address of the first GDT entry */
+} __attribute__((packed));
+
+/* IDT data structures ******************************************************
+ *
+ * The Interrupt Descriptor Table (IDT) is a data structure used by the x86
+ * architecture to implement an interrupt vector table. The IDT is used by the
+ * processor to determine the correct response to interrupts and exceptions.
+ */
+
+struct idt_entry_s
+{
+  uint16_t lobase;           /* Lower 16-bits of vector address for interrupt */
+  uint16_t sel;              /* Kernel segment selector */
+  uint8_t  zero;             /* This must always be zero */
+  uint8_t  flags;            /* (See documentation) */
+  uint16_t hibase;           /* Upper 16-bits of vector address for interrupt */
+} __attribute__((packed));
+
+/* A struct describing a pointer to an array of interrupt handlers.  This is
+ * in a format suitable for giving to 'lidt'.
+ */
+
+struct idt_ptr_s
+{
+  uint16_t limit;
+  uint32_t base;             /* The address of the first GDT entry */
 } __attribute__((packed));
 
 /****************************************************************************
@@ -156,6 +182,9 @@ extern "C" {
 #define EXTERN extern
 #endif
 
+EXTERN void gdt_flush(uint32_t gdt_addr);
+EXTERN void idt_flush(uint32_t idt_addr);
+
 #undef EXTERN
 #ifdef __cplusplus
 }
diff --git a/nuttx/arch/x86/include/i486/irq.h b/nuttx/arch/x86/include/i486/irq.h
index 0ff572df4..c82c92859 100755
--- a/nuttx/arch/x86/include/i486/irq.h
+++ b/nuttx/arch/x86/include/i486/irq.h
@@ -54,28 +54,29 @@
  * Definitions
  ****************************************************************************/
 
-/* Storage order: %ebx, $esi, %edi, %ebp, sp, and return PC */
-
-#ifdef __ASSEMBLY__
-# define REG_EBX   (0*4)
-# define REG_ESI   (1*4)
-# define REG_EDI   (2*4)
-# define REG_EBP   (3*4)
-# define REG_SP    (4*4)
-# define REG_PC    (5*4)
-# define REG_FLAGS (6*4)
-#else
-# define REG_EBX   (0)
-# define REG_ESI   (1)
-# define REG_EDI   (2)
-# define REG_EBP   (3)
-# define REG_SP    (4)
-# define REG_PC    (5)
-# define REG_FLAGS (6)
-#endif /* __ASSEMBLY__ */
+/* Common register save structgure created by up_saveusercontext() and by
+ * ISR/IRQ interrupt processing.
+ */
 
-#define XCPTCONTEXT_REGS    (7)
-#define XCPTCONTEXT_SIZE    (4 * XCPTCONTEXT_REGS)
+#define REG_DS            (0)  /* Data segment selector */
+#define REG_EDI           (1)  /* Saved by pusha */
+#define REG_ESI           (2)  /* "   " "" "   " */
+#define REG_EBP           (3)  /* "   " "" "   " */
+#define REG_ESP           (4)  /* "   " "" "   " */
+#define REG_EBX           (5)  /* "   " "" "   " */
+#define REG_EDX           (6)  /* "   " "" "   " */
+#define REG_ECX           (7)  /* "   " "" "   " */
+#define REG_EAX           (8)  /* "   " "" "   " */
+#define REG_IRQNO         (9)  /* Interrupt number */
+#define REG_ERRCODE      (10)  /* Error code */
+#define REG_EIP          (11)  /* Pushed by process on interrupt processing */
+#define REG_CS           (12)  /* "    " "" "     " "" "       " "        " */
+#define REG_EFLAGS       (13)  /* "    " "" "     " "" "       " "        " */
+#define REG_SP           (14)  /* "    " "" "     " "" "       " "        " */
+#define REG_SS           (15)  /* "    " "" "     " "" "       " "        " */
+
+#define XCPTCONTEXT_REGS (16)
+#define XCPTCONTEXT_SIZE (4 * XCPTCONTEXT_REGS)
 
 /****************************************************************************
  * Public Types
@@ -93,10 +94,12 @@ struct xcptcontext
 #ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of LR and CPSR used during signal processing. */
+  /* These are saved copies of instruction pointer and EFLAGS used during
+   * signal processing.
+   */
 
-  uint32_t saved_pc;
-  uint32_t saved_flags;
+  uint32_t saved_eip;
+  uint32_t saved_eflags;
 #endif
 
   /* Register save area */
diff --git a/nuttx/arch/x86/src/common/up_internal.h b/nuttx/arch/x86/src/common/up_internal.h
index 9730c3372..35b4e7b5c 100644
--- a/nuttx/arch/x86/src/common/up_internal.h
+++ b/nuttx/arch/x86/src/common/up_internal.h
@@ -159,7 +159,6 @@ extern int  up_saveusercontext(uint32_t *saveregs);
 extern void up_fullcontextrestore(uint32_t *restoreregs) __attribute__ ((noreturn));
 extern void up_switchcontext(uint32_t *saveregs, uint32_t *restoreregs);
 extern void up_sigdeliver(void);
-extern int  up_timerisr(int irq, uint32_t *regs);
 extern void up_lowputc(char ch);
 extern void up_puts(const char *str);
 extern void up_lowputs(const char *str);
diff --git a/nuttx/arch/x86/src/i486/i486_utils.S b/nuttx/arch/x86/src/i486/i486_utils.S
new file mode 100644
index 000000000..12a420d14
--- /dev/null
+++ b/nuttx/arch/x86/src/i486/i486_utils.S
@@ -0,0 +1,166 @@
+/****************************************************************************
+ * arch/x86/src/i486/i486_utils.S
+ *
+ *   Copyright (C) 2011 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ *   Based on Bran's kernel development tutorials. Rewritten for JamesM's
+ *   kernel development tutorials.
+ *
+ * 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 <nuttx/config.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#ifdef __CYGWIN__
+# define SYMBOL(s) _##s
+#else
+# define SYMBOL(s) s
+#endif
+
+/****************************************************************************
+ * Nasm
+ ****************************************************************************/
+
+#ifdef CONFIG_X86_NASM
+
+/****************************************************************************
+ * Nasm externals
+ ****************************************************************************/
+
+global SYMBOL(gdt_flush)
+global SYMBOL(idt_flush)
+
+/****************************************************************************
+ * Nasm macros
+ ****************************************************************************/
+
+/****************************************************************************
+ * Nasm .text
+ ****************************************************************************/
+
+SECTION .text
+BITS 32
+
+/****************************************************************************
+ * Name: gdt_flush
+ ****************************************************************************/
+
+SYMBOL(gdt_flush):
+    mov		eax, [esp+4]		/* Get the pointer to the GDT, passed as a parameter */
+    lgdt	[eax]				/* Load the new GDT pointer */
+
+    mov		ax, 0x10			/* 0x10 is the offset in the GDT to our data segment */
+    mov		ds, ax				/* Load all data segment selectors */
+    mov		es, ax
+    mov		fs, ax
+    mov		gs, ax
+    mov		ss, ax
+    jmp		0x08:.gflush		/* 0x08 is the offset to our code segment: Far jump! */
+.gflush:
+    ret
+
+/****************************************************************************
+ * Name: idt_flush
+ ****************************************************************************/
+
+SYMBOL(idt_flush):
+    mov		eax, [esp+4]		/* Get the pointer to the IDT, passed as a parameter */
+    lidt		[eax]			/* Load the IDT pointer */
+    ret
+
+#else /* !CONFIG_X86_NASM (GAS) */
+
+/****************************************************************************
+ * GAS
+ ****************************************************************************/
+
+	.file	"i486_utils.S"
+
+/****************************************************************************
+ * GAS Globals
+ ****************************************************************************/
+
+	.globl	SYMBOL(gdt_flush)
+	.globl	SYMBOL(idt_flush)
+
+/****************************************************************************
+ * GAS .text
+ ****************************************************************************/
+
+	.text
+
+/****************************************************************************
+ * Name: gdt_flush
+ ****************************************************************************/
+
+#ifndef __CYGWIN__
+	.type	SYMBOL(gdt_flush), @function
+#endif
+SYMBOL(gdt_flush):
+    movl	%eax, 4(%esp)	/* Get the pointer to the GDT, passed as a parameter */
+    lgdt	(%eax)			/* Load the new GDT pointer */
+
+    mov		%ax, 0x10		/* 0x10 is the offset in the GDT to our data segment */
+    mov		%ds, %ax		/* Load all data segment selectors */
+    mov		%es, %ax
+    mov		%fs, %ax
+    mov		%gs, %ax
+    mov		%ss, %ax
+    ljmp	*.Lgflush	/* 0x08 is the offset to our code segment: Far jump! */
+.Lgflush:
+    ret
+#ifndef __CYGWIN__
+	.size	SYMBOL(gdt_flush), . - SYMBOL(gdt_flush)
+#endif
+
+/****************************************************************************
+ * Name: idt_flush
+ ****************************************************************************/
+
+#ifndef __CYGWIN__
+	.type	SYMBOL(idt_flush), @function
+#endif
+SYMBOL(idt_flush):
+    movl	%eax, 4(%esp)	/* Get the pointer to the IDT, passed as a parameter */
+    lidt	(%eax)			/* Load the IDT pointer */
+    ret
+#ifndef __CYGWIN__
+	.size	SYMBOL(idt_flush), . - SYMBOL(idt_flush)
+#endif
+	.end
+#endif /* CONFIG_X86_NASM */
diff --git a/nuttx/arch/x86/src/i486/up_assert.c b/nuttx/arch/x86/src/i486/up_assert.c
index e9be9bcfc..69a6fe923 100644
--- a/nuttx/arch/x86/src/i486/up_assert.c
+++ b/nuttx/arch/x86/src/i486/up_assert.c
@@ -119,10 +119,19 @@ static inline void up_registerdump(void)
 
   if (current_regs)
     {
-      lldbg("ebx:%08x esi:%08x edi:%08x ebp:%08x\n",
-            current_regs[REG_EBX], current_regs[REG_ESI], current_regs[REG_EDI], current_regs[REG_EBP]);
-      lldbg(" sp:%08x  pc:%08x\n",
-            current_regs[REG_SP], current_regs[REG_PC]);
+      lldbg(" ds:%08x irq:%08x err:%08x\n",
+            current_regs[REG_DS], current_regs[REG_IRQNO],
+			current_regs[REG_ERRCODE]);
+      lldbg("edi:%08x esi:%08x ebp:%08x esp:%08x\n",
+            current_regs[REG_EDI], current_regs[REG_ESI],
+			current_regs[REG_EBP], current_regs[REG_ESP]);
+      lldbg("ebx:%08x edx:%08x ecx:%08x eax:%08x\n",
+            current_regs[REG_EBX], current_regs[REG_EDX],
+			current_regs[REG_ECX], current_regs[REG_EAX]);
+      lldbg("eip:%08x  cs:%08x flg:%08x sp:%08x ss:%08x\n",
+            current_regs[REG_EIP], current_regs[REG_CS],
+			current_regs[REG_EFLAGS], current_regs[REG_SP],
+			current_regs[REG_SS]);
     }
 }
 #else
diff --git a/nuttx/arch/x86/src/i486/up_initialstate.c b/nuttx/arch/x86/src/i486/up_initialstate.c
index e458d35b8..7bcc222d0 100644
--- a/nuttx/arch/x86/src/i486/up_initialstate.c
+++ b/nuttx/arch/x86/src/i486/up_initialstate.c
@@ -91,14 +91,14 @@ void up_initial_state(_TCB *tcb)
 
   /* Save the task entry point */
 
-  xcp->regs[REG_PC]      = (uint32_t)tcb->start;
+  xcp->regs[REG_EIP]     = (uint32_t)tcb->start;
 
   /* Enable or disable interrupts, based on user configuration.  If the IF
    * bit is set, maskable interrupts will be enabled.
    */
 
 #ifndef CONFIG_SUPPRESS_INTERRUPTS
-  xcp->regs[REG_FLAGS]   = X86_FLAGS_IF;
+  xcp->regs[REG_EFLAGS]  = X86_FLAGS_IF;
 #endif
 }
 
diff --git a/nuttx/arch/x86/src/i486/up_schedulesigaction.c b/nuttx/arch/x86/src/i486/up_schedulesigaction.c
index 6bcc3c656..7d91bb3e3 100644
--- a/nuttx/arch/x86/src/i486/up_schedulesigaction.c
+++ b/nuttx/arch/x86/src/i486/up_schedulesigaction.c
@@ -148,15 +148,15 @@ void up_schedule_sigaction(_TCB *tcb, sig_deliver_t sigdeliver)
                */
 
               tcb->xcp.sigdeliver       = sigdeliver;
-              tcb->xcp.saved_pc         = current_regs[REG_PC];
-              tcb->xcp.saved_flags      = current_regs[REG_FLAGS];
+              tcb->xcp.saved_eip        = current_regs[REG_EIP];
+              tcb->xcp.saved_eflags     = current_regs[REG_EFLAGS];
 
               /* Then set up to vector to the trampoline with interrupts
                * disabled
                */
 
-              current_regs[REG_PC]      = (uint32_t)up_sigdeliver;
-              current_regs[REG_FLAGS]   = 0;
+              current_regs[REG_EIP]     = (uint32_t)up_sigdeliver;
+              current_regs[REG_EFLAGS]  = 0;
 
               /* And make sure that the saved context in the TCB
                * is the same as the interrupt return context.
@@ -180,15 +180,15 @@ void up_schedule_sigaction(_TCB *tcb, sig_deliver_t sigdeliver)
            */
 
           tcb->xcp.sigdeliver       = sigdeliver;
-          tcb->xcp.saved_pc         = tcb->xcp.regs[REG_PC];
-          tcb->xcp.saved_flags      = tcb->xcp.regs[REG_FLAGS];
+          tcb->xcp.saved_eip        = tcb->xcp.regs[REG_EIP];
+          tcb->xcp.saved_eflags     = tcb->xcp.regs[REG_EFLAGS];
 
           /* Then set up to vector to the trampoline with interrupts
            * disabled
            */
 
-          tcb->xcp.regs[REG_PC]      = (uint32_t)up_sigdeliver;
-          tcb->xcp.regs[REG_FLAGS]   = 0;
+          tcb->xcp.regs[REG_EIP]    = (uint32_t)up_sigdeliver;
+          tcb->xcp.regs[REG_EFLAGS]  = 0;
         }
 
       irqrestore(flags);
diff --git a/nuttx/arch/x86/src/i486/up_sigdeliver.c b/nuttx/arch/x86/src/i486/up_sigdeliver.c
index 839943bcc..d39b2c6e1 100644
--- a/nuttx/arch/x86/src/i486/up_sigdeliver.c
+++ b/nuttx/arch/x86/src/i486/up_sigdeliver.c
@@ -101,8 +101,8 @@ void up_sigdeliver(void)
   /* Save the real return state on the stack. */
 
   up_copystate(regs, rtcb->xcp.regs);
-  regs[REG_PC]         = rtcb->xcp.saved_pc;
-  regs[REG_FLAGS]      = rtcb->xcp.saved_flags;
+  regs[REG_EIP]        = rtcb->xcp.saved_eip;
+  regs[REG_EFLAGS]     = rtcb->xcp.saved_eflags;
 
   /* Get a local copy of the sigdeliver function pointer. we do this so that
    * we can nullify the sigdeliver function pointer in the TCB and accept
@@ -114,7 +114,7 @@ void up_sigdeliver(void)
 
   /* Then restore the task interrupt state */
 
-  irqrestore(regs[REG_FLAGS]);
+  irqrestore(regs[REG_EFLAGS]);
 
   /* Deliver the signals */
 
diff --git a/nuttx/arch/x86/src/qemu/Make.defs b/nuttx/arch/x86/src/qemu/Make.defs
index 0010f3f3e..e44028699 100755
--- a/nuttx/arch/x86/src/qemu/Make.defs
+++ b/nuttx/arch/x86/src/qemu/Make.defs
@@ -39,7 +39,7 @@ HEAD_ASRC	= qemu_head.S
 
 # Common x86 and i486 files
 
-CMN_ASRCS	= 
+CMN_ASRCS	= i486_utils.S
 CMN_CSRCS	= up_allocateheap.c up_assert.c up_blocktask.c up_copystate.c \
 			  up_createstack.c up_mdelay.c up_udelay.c up_exit.c \
 			  up_initialize.c up_initialstate.c up_interruptcontext.c \
@@ -51,7 +51,7 @@ CMN_CSRCS	= up_allocateheap.c up_assert.c up_blocktask.c up_copystate.c \
 # Required QEMU files
 
 CHIP_ASRCS	= qemu_saveusercontext.S qemu_fullcontextrestore.S qemu_vectors.S
-CHIP_CSRCS	= qemu_idle.c qemu_irq.c qemu_lowputc.c qemu_lowsetup.c \
-			  qemu_timerisr.c
+CHIP_CSRCS	= qemu_handlers.c qemu_idle.c qemu_irq.c qemu_lowputc.c \
+			  qemu_lowsetup.c qemu_timerisr.c
 
 # Configuration-dependent QEMU files
diff --git a/nuttx/arch/x86/src/qemu/qemu_fullcontextrestore.S b/nuttx/arch/x86/src/qemu/qemu_fullcontextrestore.S
index 07023e5a0..8083c3b8f 100644
--- a/nuttx/arch/x86/src/qemu/qemu_fullcontextrestore.S
+++ b/nuttx/arch/x86/src/qemu/qemu_fullcontextrestore.S
@@ -46,7 +46,7 @@
 #include "up_internal.h"
 
 /**************************************************************************
- * Private Definitions
+ * Pre-processor Definitions
  **************************************************************************/
  
 #ifdef __CYGWIN__
@@ -90,6 +90,7 @@
 #ifdef CONFIG_X86_NASM
 #  warning "No Nasm support"
 #else
+	.file	"qemu_fullcontextrestore.S"
 	.text
 	.globl	SYMBOL(up_fullcontextrestore)
 #ifndef __CYGWIN__
@@ -104,7 +105,7 @@ SYMBOL(up_fullcontextrestore):
 
 	/* Save the return address.  */
 
-	movl	(REG_PC)(%ecx), %edx
+	movl	(REG_EIP)(%ecx), %edx
 
 	/* Restore registers.  */
 
@@ -116,7 +117,7 @@ SYMBOL(up_fullcontextrestore):
 
     /* Conditionally restore interrupts */
 
-	testl	$512, (REG_FLAGS)(%ecx)
+	testl	$512, (REG_EFLAGS)(%ecx)
 	je		.Ldisabled
 	sti
 .Ldisabled:
diff --git a/nuttx/arch/x86/src/qemu/qemu_handlers.c b/nuttx/arch/x86/src/qemu/qemu_handlers.c
new file mode 100644
index 000000000..221bfbf0f
--- /dev/null
+++ b/nuttx/arch/x86/src/qemu/qemu_handlers.c
@@ -0,0 +1,207 @@
+/****************************************************************************
+ *  arch/x86/src/qemu/qemu_handlers.c
+ *
+ *   Copyright (C) 2011 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 <nuttx/config.h>
+
+#include <nuttx/arch.h>
+#include <arch/io.h>
+
+#include "up_internal.h"
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static void idt_outb(uint8_t val, uint16_t addr) __attribute__((noinline));
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name idt_outb
+ *
+ * Description:
+ *   A slightly slower version of outb
+ *
+ ****************************************************************************/
+
+static void idt_outb(uint8_t val, uint16_t addr)
+{
+  outb(val, addr);
+}
+
+/****************************************************************************
+ * Name: common_handler
+ *
+ * Description:
+ *   Common logic for the ISR/IRQ handlers
+ *
+ ****************************************************************************/
+
+#ifndef CONFIG_SUPPRESS_INTERRUPTS
+static uint32_t *common_handler(int irq, uint32_t *regs)
+{
+  up_ledon(LED_INIRQ);
+
+  /* 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
+   * CONFIG_ARCH_INTERRUPTSTACK.
+   */
+
+  /* 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);
+  current_regs = regs;
+
+  /* Mask and acknowledge the interrupt */
+
+  up_maskack_irq(irq);
+
+  /* Deliver the IRQ */
+
+  irq_dispatch(irq, regs);
+
+  /* If a context switch occurred while processing the interrupt then
+   * current_regs may have change value.  If we return any value different
+   * from the input regs, then the lower level will know that a context
+   * switch occurred during interrupt processing.
+   */
+
+  regs = current_regs;
+
+  /* Indicate that we are no long in an interrupt handler */
+
+  current_regs = NULL;
+
+  /* Unmask the last interrupt (global interrupts are still disabled) */
+
+  up_enable_irq(irq);
+  return regs;
+}
+#endif
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: isr_handler
+ *
+ * Description:
+ *   This gets called from ISR vector handling logic in qemu_vectors.S
+ *
+ ****************************************************************************/
+
+uint32_t *isr_handler(uint32_t *regs)
+{
+#ifdef CONFIG_SUPPRESS_INTERRUPTS
+  up_ledon(LED_INIRQ);
+  PANIC(OSERR_ERREXCEPTION); /* Doesn't return */
+  return regs;               /* To keep the compiler happy */
+#else
+  uint32_t *ret;
+
+  /* Dispatch the interrupt */
+
+  up_ledon(LED_INIRQ);
+  ret = common_handler((int)regs[REG_IRQNO], regs);
+  up_ledoff(LED_INIRQ);
+  return ret;
+#endif
+}
+
+/****************************************************************************
+ * Name: isr_handler
+ *
+ * Description:
+ *   This gets called from IRQ vector handling logic in qemu_vectors.S
+ *
+ ****************************************************************************/
+
+uint32_t *irq_handler(uint32_t *regs)
+{
+#ifdef CONFIG_SUPPRESS_INTERRUPTS
+  up_ledon(LED_INIRQ);
+  PANIC(OSERR_ERREXCEPTION); /* Doesn't return */
+  return regs;               /* To keep the compiler happy */
+#else
+  uint32_t *ret;
+  int irq;
+
+  up_ledon(LED_INIRQ);
+
+  /* Get the IRQ number */
+
+  irq = (int)regs[REG_IRQNO];
+
+  /* Send an EOI (end of interrupt) signal to the PICs if this interrupt
+   * involved the slave.
+   */
+
+  if (irq >= 40)
+    {
+      /* Send reset signal to slave */
+
+      idt_outb(0x20, 0xa0);
+    }
+
+  /* Send reset signal to master */
+
+  idt_outb(0x20, 0x20);
+
+  /* Dispatch the interrupt */
+
+  ret = common_handler(irq, regs);
+  up_ledoff(LED_INIRQ);
+  return ret;
+#endif
+}
+
diff --git a/nuttx/arch/x86/src/qemu/qemu_head.S b/nuttx/arch/x86/src/qemu/qemu_head.S
index cf754408f..bef18cd60 100755
--- a/nuttx/arch/x86/src/qemu/qemu_head.S
+++ b/nuttx/arch/x86/src/qemu/qemu_head.S
@@ -43,6 +43,12 @@
  * Pre-processor definitions

  ****************************************************************************/

  

+#ifdef __CYGWIN__

+# define SYMBOL(s) _##s

+#else

+# define SYMBOL(s) s

+#endif

+

 /* Memory Map: _sbss is the start of the BSS region (see ld.script) _ebss is

  * the end of the BSS regsion (see ld.script). The idle task stack starts at

  * the end of BSS and is of size CONFIG_IDLETHREAD_STACKSIZE.  The IDLE thread

@@ -61,9 +67,9 @@
 

 #ifdef CONFIG_X86_NASM

 global		__start						/* Making entry point visible to linker */

-global		_g_heapbase					/* The start of the heap */

-extern		_os_start					/* os_start is defined elsewhere */

-extern		_up_lowsetup				/* up_lowsetup is defined elsewhere */

+global		SYMBOL(g_heapbase)			/* The start of the heap */

+extern		SYMBOL(os_start)			/* os_start is defined elsewhere */

+extern		SYMBOL(up_lowsetup)			/* up_lowsetup is defined elsewhere */

  

 /* Setting up the Multiboot header - see GRUB docs for details */

 

@@ -92,8 +98,8 @@ __start:
 

 	/* Initialize and start NuttX */

 

-	call	_up_lowsetup				/* Low-level, pre-OS initialization */

-	call	_os_start					/* Start NuttX */

+	call	SYMBOL(up_lowsetup)			/* Low-level, pre-OS initialization */

+	call	SYMBOL(os_start)			/* Start NuttX */

  

 	/* NuttX will not return */

 

@@ -129,7 +135,7 @@ section .rodata
  */

 

 align 4

-g_heapbase:

+SYMBOL(g_heapbase):

 	dd	_ebss

 

 #else /* !CONFIG_X86_NASM (GAS) */

@@ -138,10 +144,11 @@ g_heapbase:
  * GAS .text

  ****************************************************************************/

 

+	.file	"qemu_head.S"

 	.global	__start						/* Making entry point visible to linker */

-	.global	_os_start					/* os_start is defined elsewhere */

-	.global	_up_lowsetup				/* up_lowsetup is defined elsewhere */

-	.global	_g_heapbase					/* The start of the heap */

+	.global	SYMBOL(os_start)			/* os_start is defined elsewhere */

+	.global	SYMBOL(up_lowsetup)			/* up_lowsetup is defined elsewhere */

+	.global	SYMBOL(g_heapbase)			/* The start of the heap */

 

 	/* Setting up the Multiboot header - see GRUB docs for details */

 

@@ -157,6 +164,9 @@ g_heapbase:
 	.long	FLAGS

 	.long	CHECKSUM

 

+#ifndef __CYGWIN__

+	.type	__start, @function

+#endif

 __start:

 	/* Set up the stack */

 

@@ -169,8 +179,8 @@ __start:
 

 	/* Initialize and start NuttX */

 

-	call	_up_lowsetup				/* Low-level, pre-OS initialization */

-	call	_os_start					/* Start NuttX */

+	call	SYMBOL(up_lowsetup)			/* Low-level, pre-OS initialization */

+	call	SYMBOL(os_start)			/* Start NuttX */

 

 	/* NuttX will not return */

 

@@ -178,6 +188,9 @@ __start:
 hang:

 	hlt									/* Halt machine should NuttX return */

 	jmp	hang

+#ifndef __CYGWIN__

+	.size	__start, . - __start

+#endif

 

 /****************************************************************************

  * .bss

@@ -189,7 +202,13 @@ hang:
  * do in the system (see up_idle()).

  */

 

+#ifndef __CYGWIN__

+	.type	idle_stack, @object

+#endif

 	.comm   idle_stack, CONFIG_IDLETHREAD_STACKSIZE, 32

+#ifndef __CYGWIN__

+	.size	idle_stack, . - idle_stack

+#endif

 

 /****************************************************************************

  * .rodata

@@ -202,7 +221,13 @@ hang:
  * until the end of memory.

  */

 

-_g_heapbase:

+#ifndef __CYGWIN__

+	.type	SYMBOL(g_heapbase), @object

+#endif

+SYMBOL(g_heapbase):

 	.word	_ebss

+#ifndef __CYGWIN__

+	.size	SYMBOL(g_heapbase), . - SYMBOL(g_heapbase)

+#endif

 	.end

 #endif /* CONFIG_X86_NASM */
\ No newline at end of file
diff --git a/nuttx/arch/x86/src/qemu/qemu_internal.h b/nuttx/arch/x86/src/qemu/qemu_internal.h
index 601f84b77..c8bd5cd95 100755
--- a/nuttx/arch/x86/src/qemu/qemu_internal.h
+++ b/nuttx/arch/x86/src/qemu/qemu_internal.h
@@ -380,6 +380,65 @@ EXTERN void i486_dmadump(DMA_HANDLE handle, const struct i486_dmaregs_s *regs,
 #endif
 #endif
 
+/****************************************************************************
+ * Name: vector_*
+ *
+ * Description:
+ *   These are the various ISR/IRQ vector address exported from
+ *   qemu_vectors.S.  These addresses need to have global scope so that they
+ *   can be known to the interrupt intialization logic in qemu_irq.c.
+ *
+ ****************************************************************************/
+
+EXTERN void vector_isr0(void);
+EXTERN void vector_isr1(void);
+EXTERN void vector_isr2(void);
+EXTERN void vector_isr3(void);
+EXTERN void vector_isr4(void);
+EXTERN void vector_isr5(void);
+EXTERN void vector_isr6(void);
+EXTERN void vector_isr7(void);
+EXTERN void vector_isr8(void);
+EXTERN void vector_isr9(void);
+EXTERN void vector_isr10(void);
+EXTERN void vector_isr11(void);
+EXTERN void vector_isr12(void);
+EXTERN void vector_isr13(void);
+EXTERN void vector_isr14(void);
+EXTERN void vector_isr15(void);
+EXTERN void vector_isr16(void);
+EXTERN void vector_isr17(void);
+EXTERN void vector_isr18(void);
+EXTERN void vector_isr19(void);
+EXTERN void vector_isr20(void);
+EXTERN void vector_isr21(void);
+EXTERN void vector_isr22(void);
+EXTERN void vector_isr23(void);
+EXTERN void vector_isr24(void);
+EXTERN void vector_isr25(void);
+EXTERN void vector_isr26(void);
+EXTERN void vector_isr27(void);
+EXTERN void vector_isr28(void);
+EXTERN void vector_isr29(void);
+EXTERN void vector_isr30(void);
+EXTERN void vector_isr31(void);
+EXTERN void vector_irq0(void);
+EXTERN void vector_irq1(void);
+EXTERN void vector_irq2(void);
+EXTERN void vector_irq3(void);
+EXTERN void vector_irq4(void);
+EXTERN void vector_irq5(void);
+EXTERN void vector_irq6(void);
+EXTERN void vector_irq7(void);
+EXTERN void vector_irq8(void);
+EXTERN void vector_irq9(void);
+EXTERN void vector_irq10(void);
+EXTERN void vector_irq11(void);
+EXTERN void vector_irq12(void);
+EXTERN void vector_irq13(void);
+EXTERN void vector_irq14(void);
+EXTERN void vector_irq15(void);
+
 #undef EXTERN
 #if defined(__cplusplus)
 }
diff --git a/nuttx/arch/x86/src/qemu/qemu_irq.c b/nuttx/arch/x86/src/qemu/qemu_irq.c
index 6d16cfc92..be6c4a40e 100755
--- a/nuttx/arch/x86/src/qemu/qemu_irq.c
+++ b/nuttx/arch/x86/src/qemu/qemu_irq.c
@@ -41,11 +41,13 @@
 #include <nuttx/config.h>
 
 #include <stdint.h>
+#include <string.h>
 #include <debug.h>
 
 #include <nuttx/irq.h>
 #include <nuttx/arch.h>
 #include <arch/irq.h>
+#include <arch/io.h>
 
 #include "up_arch.h"
 #include "os_internal.h"
@@ -57,6 +59,16 @@
  ****************************************************************************/
 
 /****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static void idt_outb(uint8_t val, uint16_t addr) __attribute__((noinline));
+static void up_remappic(void);
+static void up_idtentry(struct idt_entry_s *entry, uint32_t base,
+                        uint16_t sel, uint8_t flags);
+static inline void up_idtinit(void);
+
+/****************************************************************************
  * Public Data
  ****************************************************************************/
 
@@ -71,6 +83,159 @@ uint32_t *current_regs;
  ****************************************************************************/
 
 /****************************************************************************
+ * Name idt_outb
+ *
+ * Description:
+ *   A slightly slower version of outb
+ *
+ ****************************************************************************/
+
+static void idt_outb(uint8_t val, uint16_t addr)
+{
+  outb(val, addr);
+}
+
+/****************************************************************************
+ * Name up_remappic
+ *
+ * Description:
+ *   Remap the PIC.  The Programmable Interrupt Controller (PIC) is used to
+ *   combine several sources of interrupt onto one or more CPU lines, while
+ *   allowing priority levels to be assigned to its interrupt outputs. When
+ *   the device has multiple interrupt outputs to assert, it will assert them
+ *   in the order of their relative priority. 
+ *
+ ****************************************************************************/
+
+static void up_remappic(void)
+{
+  /* Mask interrupts from PIC */
+
+  idt_outb(0xff, 0x21);
+  idt_outb(0xff, 0xA1);
+
+  /* Remap the irq table for primary */
+
+  idt_outb(0x11, 0x20);
+  idt_outb(0x20, 0x21);
+  idt_outb(0x04, 0x21);
+  idt_outb(0x01, 0x21);
+  
+  /* Remap irq for slave */
+
+  idt_outb(0x11, 0xA0);
+  idt_outb(0x28, 0xA1);
+  idt_outb(0x02, 0xA1);
+  idt_outb(0x01, 0xA1);    
+
+  /* Enable IRQ0 on the master with the mask */
+
+  idt_outb( 0xff, 0xA1);
+  idt_outb( 0xfe, 0x21);
+}
+
+/****************************************************************************
+ * Name up_idtentry
+ *
+ * Description:
+ *   Initialize one IDT entry. 
+ *
+ ****************************************************************************/
+
+static void up_idtentry(struct idt_entry_s *entry, uint32_t base,
+                        uint16_t sel, uint8_t flags)
+{
+  entry->lobase = base & 0xFFFF;
+  entry->hibase = (base >> 16) & 0xFFFF;
+
+  entry->sel    = sel;
+  entry->zero   = 0;
+
+  /* We must uncomment the OR below when we get to using user-mode. It sets the
+   * interrupt gate's privilege level to 3.
+   */
+
+  entry->flags  = flags /* | 0x60 */;
+}
+
+/****************************************************************************
+ * Name up_idtinit
+ *
+ * Description:
+ *   Initialize the IDT. The Interrupt Descriptor Table (IDT) is a data
+ *   structure used by the x86 architecture to implement an interrupt vector
+ *   table. The IDT is used by the processor to determine the correct
+ *   response to interrupts and exceptions.
+ *
+ ****************************************************************************/
+
+static inline void up_idtinit(void)
+{
+  /* This uses a ton of stack! */
+
+  struct idt_entry_s idt_entries[256];
+  struct idt_ptr_s   idt_ptr;
+
+  idt_ptr.limit = sizeof(struct idt_entry_s) * 256 - 1;
+  idt_ptr.base  = (uint32_t)&idt_entries;
+
+  memset(&idt_entries, 0, sizeof(struct idt_entry_s)*256);
+
+  up_remappic();
+
+  up_idtentry(&idt_entries[0],  (uint32_t)vector_isr0 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[1],  (uint32_t)vector_isr1 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[2],  (uint32_t)vector_isr2 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[3],  (uint32_t)vector_isr3 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[4],  (uint32_t)vector_isr4 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[5],  (uint32_t)vector_isr5 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[6],  (uint32_t)vector_isr6 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[7],  (uint32_t)vector_isr7 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[8],  (uint32_t)vector_isr8 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[9],  (uint32_t)vector_isr9 , 0x08, 0x8e);
+  up_idtentry(&idt_entries[10], (uint32_t)vector_isr10, 0x08, 0x8e);
+  up_idtentry(&idt_entries[11], (uint32_t)vector_isr11, 0x08, 0x8e);
+  up_idtentry(&idt_entries[12], (uint32_t)vector_isr12, 0x08, 0x8e);
+  up_idtentry(&idt_entries[13], (uint32_t)vector_isr13, 0x08, 0x8e);
+  up_idtentry(&idt_entries[14], (uint32_t)vector_isr14, 0x08, 0x8e);
+  up_idtentry(&idt_entries[15], (uint32_t)vector_isr15, 0x08, 0x8e);
+  up_idtentry(&idt_entries[16], (uint32_t)vector_isr16, 0x08, 0x8e);
+  up_idtentry(&idt_entries[17], (uint32_t)vector_isr17, 0x08, 0x8e);
+  up_idtentry(&idt_entries[18], (uint32_t)vector_isr18, 0x08, 0x8e);
+  up_idtentry(&idt_entries[19], (uint32_t)vector_isr19, 0x08, 0x8e);
+  up_idtentry(&idt_entries[20], (uint32_t)vector_isr20, 0x08, 0x8e);
+  up_idtentry(&idt_entries[21], (uint32_t)vector_isr21, 0x08, 0x8e);
+  up_idtentry(&idt_entries[22], (uint32_t)vector_isr22, 0x08, 0x8e);
+  up_idtentry(&idt_entries[23], (uint32_t)vector_isr23, 0x08, 0x8e);
+  up_idtentry(&idt_entries[24], (uint32_t)vector_isr24, 0x08, 0x8e);
+  up_idtentry(&idt_entries[25], (uint32_t)vector_isr25, 0x08, 0x8e);
+  up_idtentry(&idt_entries[26], (uint32_t)vector_isr26, 0x08, 0x8e);
+  up_idtentry(&idt_entries[27], (uint32_t)vector_isr27, 0x08, 0x8e);
+  up_idtentry(&idt_entries[28], (uint32_t)vector_isr28, 0x08, 0x8e);
+  up_idtentry(&idt_entries[29], (uint32_t)vector_isr29, 0x08, 0x8e);
+  up_idtentry(&idt_entries[30], (uint32_t)vector_isr30, 0x08, 0x8e);
+  up_idtentry(&idt_entries[31], (uint32_t)vector_isr31, 0x08, 0x8e);
+  up_idtentry(&idt_entries[32], (uint32_t)vector_irq0, 0x08, 0x8e);
+  up_idtentry(&idt_entries[33], (uint32_t)vector_irq1, 0x08, 0x8e);
+  up_idtentry(&idt_entries[34], (uint32_t)vector_irq2, 0x08, 0x8e);
+  up_idtentry(&idt_entries[35], (uint32_t)vector_irq3, 0x08, 0x8e);
+  up_idtentry(&idt_entries[36], (uint32_t)vector_irq4, 0x08, 0x8e);
+  up_idtentry(&idt_entries[37], (uint32_t)vector_irq5, 0x08, 0x8e);
+  up_idtentry(&idt_entries[38], (uint32_t)vector_irq6, 0x08, 0x8e);
+  up_idtentry(&idt_entries[39], (uint32_t)vector_irq7, 0x08, 0x8e);
+  up_idtentry(&idt_entries[40], (uint32_t)vector_irq8, 0x08, 0x8e);
+  up_idtentry(&idt_entries[41], (uint32_t)vector_irq9, 0x08, 0x8e);
+  up_idtentry(&idt_entries[42], (uint32_t)vector_irq10, 0x08, 0x8e);
+  up_idtentry(&idt_entries[43], (uint32_t)vector_irq11, 0x08, 0x8e);
+  up_idtentry(&idt_entries[44], (uint32_t)vector_irq12, 0x08, 0x8e);
+  up_idtentry(&idt_entries[45], (uint32_t)vector_irq13, 0x08, 0x8e);
+  up_idtentry(&idt_entries[46], (uint32_t)vector_irq14, 0x08, 0x8e);
+  up_idtentry(&idt_entries[47], (uint32_t)vector_irq15, 0x08, 0x8e);
+
+  idt_flush((uint32_t)&idt_ptr);
+}
+
+/****************************************************************************
  * Public Functions
  ****************************************************************************/
 
@@ -80,19 +245,13 @@ uint32_t *current_regs;
 
 void up_irqinitialize(void)
 {
-  /* Disable all interrupts */
-
   /* currents_regs is non-NULL only while processing an interrupt */
 
   current_regs = NULL;
 
-  /* Initialize logic to support a second level of interrupt decoding for
-   * GPIO pins.
-   */
- 
-#ifdef CONFIG_GPIO_IRQ
-  lpc17_gpioirqinitialize();
-#endif
+  /* Initialize the IDT */
+
+  up_idtinit();
 
   /* And finally, enable interrupts */
 
diff --git a/nuttx/arch/x86/src/qemu/qemu_lowsetup.c b/nuttx/arch/x86/src/qemu/qemu_lowsetup.c
index aac19042d..bbc7f1229 100644
--- a/nuttx/arch/x86/src/qemu/qemu_lowsetup.c
+++ b/nuttx/arch/x86/src/qemu/qemu_lowsetup.c
@@ -96,11 +96,11 @@ static void up_gdtinit(void)
   struct gdt_entry_s gdt_entries[5];
   struct gdt_ptr_s   gdt_ptr;
 
-  up_gdtentry(0, 0, 0, 0, 0);                /* Null segment */
-  up_gdtentry(1, 0, 0xffffffff, 0x9a, 0xcf); /* Code segment */
-  up_gdtentry(2, 0, 0xffffffff, 0x92, 0xcf); /* Data segment */
-  up_gdtentry(3, 0, 0xffffffff, 0xfa, 0xcf); /* User mode code segment */
-  up_gdtentry(4, 0, 0xffffffff, 0xf2, 0xcf); /* User mode data segment */
+  up_gdtentry(&gdt_entries[0], 0, 0, 0, 0);                /* Null segment */
+  up_gdtentry(&gdt_entries[1], 0, 0xffffffff, 0x9a, 0xcf); /* Code segment */
+  up_gdtentry(&gdt_entries[2], 0, 0xffffffff, 0x92, 0xcf); /* Data segment */
+  up_gdtentry(&gdt_entries[3], 0, 0xffffffff, 0xfa, 0xcf); /* User mode code segment */
+  up_gdtentry(&gdt_entries[4], 0, 0xffffffff, 0xf2, 0xcf); /* User mode data segment */
 
   gdt_ptr.limit = (sizeof(struct gdt_entry_s) * 5) - 1;
   gdt_ptr.base  = (uint32_t)gdt_entries;
@@ -122,7 +122,9 @@ static void up_gdtinit(void)
 
 void up_lowsetup(void)
 {
-  /* Perform chip-specific initializations */
+  /* Initialize the Global descriptor table */
+
+  up_gdtinit();
 
   /* Now perform board-specific initializations */
 
diff --git a/nuttx/arch/x86/src/qemu/qemu_saveusercontext.S b/nuttx/arch/x86/src/qemu/qemu_saveusercontext.S
index cc4641835..dc352c181 100644
--- a/nuttx/arch/x86/src/qemu/qemu_saveusercontext.S
+++ b/nuttx/arch/x86/src/qemu/qemu_saveusercontext.S
@@ -90,6 +90,7 @@
 #ifdef CONFIG_X86_NASM
 #  warning "No Nasm support"
 #else
+	.file	"qemu_saveusercontext.S"
 	.text
 	.globl	SYMBOL(up_saveusercontext)
 #ifndef __CYGWIN__
@@ -113,7 +114,7 @@ SYMBOL(up_saveusercontext):
 	/* Save the return PC */
 
 	movl	0(%esp), %ecx
-	movl	%ecx, (REG_PC)(%eax)
+	movl	%ecx, (REG_EIP)(%eax)
 
 	/* Save the framepointer */
 
@@ -123,7 +124,7 @@ SYMBOL(up_saveusercontext):
 
     pushf
     pop		%ecx
-	movl	%ecx, (REG_FLAGS)(%eax)
+	movl	%ecx, (REG_EFLAGS)(%eax)
  
 	/* And return 0 */
 
diff --git a/nuttx/arch/x86/src/qemu/qemu_timerisr.c b/nuttx/arch/x86/src/qemu/qemu_timerisr.c
index 072a54aa9..ddc4a5e74 100755
--- a/nuttx/arch/x86/src/qemu/qemu_timerisr.c
+++ b/nuttx/arch/x86/src/qemu/qemu_timerisr.c
@@ -4,6 +4,9 @@
  *   Copyright (C) 2011 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
  *
+ *   Based on Bran's kernel development tutorials. Rewritten for JamesM's
+ *   kernel development tutorials.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ -44,6 +47,7 @@
 #include <debug.h>
 
 #include <nuttx/arch.h>
+#include <arch/io.h>
 #include <arch/board/board.h>
 
 #include "clock_internal.h"
@@ -54,9 +58,30 @@
 #include "qemu_internal.h"
 
 /****************************************************************************
- * Definitions
+ * Pre-processor Definitions
  ****************************************************************************/
 
+/* Programmable interval timer (PIT)
+ *
+ *   Fpit = Fin / divisor
+ *   divisor = Fin / divisor
+ *
+ * Where:
+ *
+ *   Fpit = The desired interrupt frequency.
+ *   Fin  = PIT input frequency (PIT_CLOCK provided in board.h)
+ *
+ * The desired timer interrupt frequency is provided by the definition CLK_TCK
+ * (see include/time.h).  CLK_TCK defines the desired number of system clock
+ * ticks per second.  That value is a user configurable setting that defaults
+ * to 100 (100 ticks per second = 10 MS interval).
+ */
+
+#define PIT_DIVISOR  ((uint32_t)PIT_CLOCK/(uint32_t)CLK_TCK)
+
+#define PIT_MODE     0x43
+#define PIT_CH0      0x40
+
 /****************************************************************************
  * Private Types
  ****************************************************************************/
@@ -65,6 +90,43 @@
  * Private Function Prototypes
  ****************************************************************************/
 
+static void pit_outb(uint8_t val, uint16_t addr) __attribute__((noinline));
+static int up_timerisr(int irq, uint32_t *regs);
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name pit_outb
+ *
+ * Description:
+ *   A slightly slower version of outb
+ *
+ ****************************************************************************/
+
+static void pit_outb(uint8_t val, uint16_t addr)
+{
+  outb(val, addr);
+}
+
+/****************************************************************************
+ * Function:  up_timerisr
+ *
+ * Description:
+ *   The timer ISR will perform a variety of services for various portions
+ *   of the systems.
+ *
+ ****************************************************************************/
+
+static int up_timerisr(int irq, uint32_t *regs)
+{
+   /* Process timer interrupt */
+
+   sched_process_timer();
+   return 0;
+}
+
 /****************************************************************************
  * Global Functions
  ****************************************************************************/
@@ -80,5 +142,21 @@
 
 void up_timerinit(void)
 {
-#warning "Not implemented"
+  /* uint32_t to avoid compile time overflow errors */
+
+  uint32_t divisor = PIT_DIVISOR;
+  DEBUGASSERT(divisor <= 0xffff);
+
+  /* Attach to the timer interrupt handler */
+
+  (void)irq_attach(IRQ0, (xcpt_t)up_timerisr);
+
+  /* Send the command byte */
+
+  pit_outb(0x36, PIT_MODE);
+
+  /* Set the PIT input frequency divisor */
+
+  pit_outb((uint8_t)(divisor & 0xff),  PIT_CH0);
+  pit_outb((uint8_t)((divisor >> 8) & 0xff), PIT_CH0);
 }
diff --git a/nuttx/arch/x86/src/qemu/qemu_vectors.S b/nuttx/arch/x86/src/qemu/qemu_vectors.S
index 93cac4b3d..2d66ca01c 100755
--- a/nuttx/arch/x86/src/qemu/qemu_vectors.S
+++ b/nuttx/arch/x86/src/qemu/qemu_vectors.S
@@ -47,6 +47,12 @@
  * Pre-processor Definitions
  ****************************************************************************/
 
+#ifdef __CYGWIN__
+# define SYMBOL(s) _##s
+#else
+# define SYMBOL(s) s
+#endif
+
 #define KSEG 0x10
 
 /****************************************************************************
@@ -54,8 +60,17 @@
  ****************************************************************************/
 
 #ifdef CONFIG_X86_NASM
-extern _irq_handler
-extern _isr_handler
+
+/****************************************************************************
+ * Nasm externals
+ ****************************************************************************/
+
+extern SYMBOL(irq_handler)
+extern SYMBOL(isr_handler)
+
+/****************************************************************************
+ * Nasm macros
+ ****************************************************************************/
 
 /* Trace macros, use like trace 'i' to print char to serial port. */
 
@@ -74,8 +89,8 @@ extern _isr_handler
  */
 
 %macro ISR_NOERRCODE 1
-  global	vector_isr%1
-  vector_isr%1:
+  global	SYMBOL(vector_isr%1)
+  SYMBOL(vector_isr%1):
 	cli							/* Disable interrupts firstly. */
 	push	byte 0				/* Push a dummy error code. */
 	push	byte %1				/* Push the interrupt number. */
@@ -87,8 +102,8 @@ extern _isr_handler
  */
 
 %macro ISR_ERRCODE 1
-  global	vector_isr%1
-  vector_isr%1:
+  global	SYMBOL(vector_isr%1)
+  SYMBOL(vector_isr%1):
 	cli							/* Disable interrupts. */
 	push	byte %1				/* Push the interrupt number */
 	jmp		isr_common
@@ -99,14 +114,18 @@ extern _isr_handler
  */
 
 %macro IRQ 2
-  global	vector_irq%1
-  vector_irq%1:
+  global	SYMBOL(vector_irq%1)
+  SYMBOL(vector_irq%1):
 	cli
 	push	byte 0
 	push	byte %2
 	jmp		irq_common
 %endmacro
 		
+/****************************************************************************
+ * Nasm vectors
+ ****************************************************************************/
+
 /* The following will be the vector address programmed into the IDT */
 
 ISR_NOERRCODE		ISR0
@@ -158,10 +177,15 @@ IRQ				13,	IRQ13
 IRQ				14,	IRQ14
 IRQ				15,	IRQ15
 
-/* This is our common ISR stub. It saves the processor state, sets up for
- * kernel mode segments, calls the C-level fault handler, and finally restores
- * the stack frame.
- */
+/****************************************************************************
+ * Name: isr_common
+ *
+ * Description:
+ *   This is the common ISR logic. It saves the processor state, sets up for
+ *   kernel mode segments, calls the C-level fault handler, and finally
+ *   restores the stack frame.
+ *
+ ****************************************************************************/
 
 isr_common:
 /*	trace	'S' */
@@ -176,7 +200,7 @@ isr_common:
 	mov		fs, ax
 	mov		gs, ax
 
-	call	_isr_handler
+	call	SYMBOL(isr_handler)
 
 	pop		ebx					/* Reload the original data segment descriptor */
 	mov		ds, bx
@@ -189,10 +213,15 @@ isr_common:
 	sti
 	iret						/* Pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP */
 
-/* This is our common IRQ stub. It saves the processor state, sets up for
- * kernel mode segments, calls the C-level fault handler, and finally restores
- * the stack frame.
- */
+/****************************************************************************
+ * Name: irq_common
+ *
+ * Description:
+ *   This is the common IRQ logic. It saves the processor state, sets up for
+ *   kernel mode segments, calls the C-level fault handler, and finally
+ *   restores the stack frame.
+ *
+ ****************************************************************************/
 
 irq_common:
 /*	trace	'R' */
@@ -207,7 +236,7 @@ irq_common:
 	mov		fs, ax
 	mov		gs, ax
 
-	call	_irq_handler
+	call	SYMBOL(irq_handler)
 
 	pop		ebx					/* Reload the original data segment descriptor */
 	mov		ds, bx
@@ -226,8 +255,18 @@ irq_common:
  * GAS .text
  ****************************************************************************/
 
-	.globl	_irq_handler
-	.globl	_isr_handler
+	.file	"qemu_vectors.S"
+
+/****************************************************************************
+ * GAS globals
+ ****************************************************************************/
+
+	.globl	SYMBOL(irq_handler)
+	.globl	SYMBOL(isr_handler)
+
+/****************************************************************************
+ * GAS macros
+ ****************************************************************************/
 
 /* Trace macros, use like trace 'i' to print char to serial port. */
 
@@ -246,8 +285,8 @@ irq_common:
  */
 
 	.macro ISR_NOERRCODE, intno
-	.globl	vector_isr\intno
-vector_isr\intno:
+	.globl	SYMBOL(vector_isr\intno)
+SYMBOL(vector_isr\intno):
 	cli							/* Disable interrupts firstly. */
 	push	$0					/* Push a dummy error code. */
 	push	$\intno				/* Push the interrupt number. */
@@ -259,8 +298,8 @@ vector_isr\intno:
  */
 
 	.macro	ISR_ERRCODE, intno
-	.globl	vector_isr\intno
-vector_isr\intno:
+	.globl	SYMBOL(vector_isr\intno)
+SYMBOL(vector_isr\intno):
 	cli							/* Disable interrupts firstly. */
 	push	$\intno				/* Push the interrupt number. */
 	jmp		isr_common			/* Go to the common handler code. */
@@ -271,8 +310,8 @@ vector_isr\intno:
  */
 
 	.macro	IRQ, irqno, intno
-	.globl	vector_irq\irqno
-vector_irq\irqno:
+	.globl	SYMBOL(vector_irq\irqno)
+SYMBOL(vector_irq\irqno):
 	cli							/* Disable interrupts firstly. */
 	push	$0					/* Push a dummy error code. */
 	push	$\intno				/* Push the interrupt number. */
@@ -330,66 +369,88 @@ vector_irq\irqno:
 	IRQ				14,	IRQ14
 	IRQ				15,	IRQ15
 
-/* This is our common ISR stub. It saves the processor state, sets up for
- * kernel mode segments, calls the C-level fault handler, and finally restores
- * the stack frame.
- */
+/****************************************************************************
+ * Name: isr_common
+ *
+ * Description:
+ *   This is the common ISR logic. It saves the processor state, sets up for
+ *   kernel mode segments, calls the C-level fault handler, and finally
+ *   restores the stack frame.
+ *
+ ****************************************************************************/
 
+#ifndef __CYGWIN__
+	.type	isr_common, @function
+#endif
 isr_common:
 /*	trace	'S' */
 	pusha						/* Pushes edi,esi,ebp,esp,ebx,edx,ecx,eax */
 
-	mov		%ax, ds				/* Lower 16-bits of eax = ds. */
+	mov		%ax, %ds			/* Lower 16-bits of eax = ds. */
 	pushl	%eax				/* Save the data segment descriptor */
 
 	mov		%ax, KSEG			/* Load the kernel data segment descriptor */
-	mov		ds, %ax
-	mov		es, %ax
-	mov		fs, %ax
-	mov		gs, %ax
+	mov		%ds, %ax
+	mov		%es, %ax
+	mov		%fs, %ax
+	mov		%gs, %ax
 
-	call	_isr_handler
+	call	SYMBOL(isr_handler)
 
-	pop		ebx					/* Reload the original data segment descriptor */
-	mov		ds, %bx
-	mov		es, %bx
-	mov		fs, %bx
-	mov		gs, %bx
+	pop		%ebx				/* Reload the original data segment descriptor */
+	mov		%ds, %bx
+	mov		%es, %bx
+	mov		%fs, %bx
+	mov		%gs, %bx
 
 	popa						/* Pops edi,esi,ebp... */
 	add		%esp, 8				/* Cleans up the pushed error code and pushed ISR number */
 	sti
+#ifndef __CYGWIN__
+	.size	isr_common, . - isr_common
+#endif
 	iret						/* Pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP */
 
-/* This is our common IRQ stub. It saves the processor state, sets up for
- * kernel mode segments, calls the C-level fault handler, and finally restores
- * the stack frame.
- */
+/****************************************************************************
+ * Name: irq_common
+ *
+ * Description:
+ *   This is the common IRQ logic. It saves the processor state, sets up for
+ *   kernel mode segments, calls the C-level fault handler, and finally
+ *   restores the stack frame.
+ *
+ ****************************************************************************/
 
+#ifndef __CYGWIN__
+	.type	irq_common, @function
+#endif
 irq_common:
 /*	trace	'R' */
 	pusha						/* Pushes edi,esi,ebp,esp,ebx,edx,ecx,eax */
 
-	mov		%ax, ds				/* Lower 16-bits of eax = ds. */
+	mov		%ax, %ds				/* Lower 16-bits of eax = ds. */
 	push	%eax				/* Save the data segment descriptor */
 
 	mov		%ax, KSEG			/* Load the kernel data segment descriptor */
-	mov		ds, %ax
-	mov		es, %ax
-	mov		fs, %ax
-	mov		gs, %ax
+	mov		%ds, %ax
+	mov		%es, %ax
+	mov		%fs, %ax
+	mov		%gs, %ax
 
-	call	_irq_handler
+	call	SYMBOL(irq_handler)
 
 	pop		%ebx				/* Reload the original data segment descriptor */
-	mov		ds, %bx
-	mov		es, %bx
-	mov		fs, %bx
-	mov		gs, %bx
+	mov		%ds, %bx
+	mov		%es, %bx
+	mov		%fs, %bx
+	mov		%gs, %bx
 
 	popa						/* Pops edi,esi,ebp... */
 	add		%esp, 8				/* Cleans up the pushed error code and pushed ISR number */
 	sti
 	iret						/* Pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP */
+#ifndef __CYGWIN__
+	.size	irq_common, . - irq_common
+#endif
 	.end
 #endif /* CONFIG_X86_NASM */
diff --git a/nuttx/configs/qemu-i486/include/board.h b/nuttx/configs/qemu-i486/include/board.h
index 35f98987c..31ae72dc4 100755
--- a/nuttx/configs/qemu-i486/include/board.h
+++ b/nuttx/configs/qemu-i486/include/board.h
@@ -49,6 +49,10 @@
 
 /* Clocking *************************************************************************/
 
+/* Programmable interval timer (PIT) */
+
+#define PIT_CLOCK 1041816 /* PIT input clock */
+
 /* LED definitions ******************************************************************/
 
 /* Button definitions ***************************************************************/