Skeletons for remaining paging files to be implemented

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@2863 42af7a65-404d-4744-a932-0658087f49c3

8 files changed, 464 insertions, 6 deletions

diff --git a/nuttx/arch/arm/src/arm/up_allocpage.c b/nuttx/arch/arm/src/arm/up_allocpage.c
new file mode 100755
index 000000000..499edc9da
--- /dev/null
+++ b/nuttx/arch/arm/src/arm/up_allocpage.c
@@ -0,0 +1,114 @@
+/****************************************************************************
+ * arch/arm/src/arm/up_allocpage.c
+ * Allocate a new page and map it to the fault address of a task.
+ *
+ *   Copyright (C) 2010 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 <debug.h>
+
+#include <nuttx/sched.h>
+#include <nuttx/page.h>
+
+#ifdef CONFIG_PAGING
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_allocpage()
+ *
+ * Description:
+ *  This architecture-specific function will set aside page in memory and map
+ *  the page to its correct virtual address.  Architecture-specific context
+ *  information saved within the TCB will provide the function with the
+ *  information needed to identify the virtual miss address.
+ *
+ *  This function will return the allocated physical page address in vpage.
+ *  The size of the underlying physical page is determined by the
+ *  configuration setting CONFIG_PAGING_PAGESIZE.
+ *
+ *  NOTE 1: This function must always return a page allocation. If all
+ *  available pages are in-use (the typical case), then this function will
+ *  select a page in-use, un-map it, and make it available.
+ *
+ *  NOTE 2: Allocating and filling a page is a two step process.  up_allocpage()
+ *  allocates the page, and up_fillpage() fills it with data from some non-
+ *  volatile storage device.  This distinction is made because up_allocpage()
+ *  can probably be implemented in board-independent logic whereas up_fillpage()
+ *  probably must be implemented as board-specific logic.
+ *
+ * Input Parameters:
+ *   tcb - A reference to the task control block of the task that needs to
+ *         have a page fill.  Architecture-specific logic can retrieve page
+ *         fault information from the architecture-specific context
+ *         information in this TCB to perform the mapping.
+ *
+ * Returned Value:
+ *   This function will return zero (OK) if the allocation was successful.
+ *   A negated errno value may be returned if an error occurs.  All errors,
+ *   however, are fatal.
+ *
+ * Assumptions:
+ *   - This function is called from the normal tasking context (but with
+ *     interrupts disabled).  The implementation must take whatever actions
+ *     are necessary to assure that the operation is safe within this
+ *     context.
+ *
+ ****************************************************************************/
+
+int up_allocpage(FAR _TCB *tcb, FAR void **vpage);
+{
+# warning "Not implemented"
+  return -ENOSYS;
+}
+
+#endif /* CONFIG_PAGING */
diff --git a/nuttx/arch/arm/src/arm/up_checkmapping.c b/nuttx/arch/arm/src/arm/up_checkmapping.c
new file mode 100755
index 000000000..9f7aa5c3f
--- /dev/null
+++ b/nuttx/arch/arm/src/arm/up_checkmapping.c
@@ -0,0 +1,103 @@
+/****************************************************************************
+ * arch/arm/src/arm/up_checkmapping.c
+ * Check if the current task's fault address has been mapped into the virtual
+ * address space.
+ *
+ *   Copyright (C) 2010 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 <debug.h>
+
+#include <nuttx/sched.h>
+#include <nuttx/page.h>
+
+#ifdef CONFIG_PAGING
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_checkmapping()
+ *
+ * Description:
+ *  The function up_checkmapping() returns an indication if the page fill
+ *  still needs to performed or not. In certain conditions, the page fault
+ *  may occur on several threads and be queued multiple times. This function
+ *  will prevent the same page from be filled multiple times.
+ *
+ * Input Parameters:
+ *   tcb - A reference to the task control block of the task that we believe
+ *         needs to have a page fill.  Architecture-specific logic can
+ *         retrieve page fault information from the architecture-specific
+ *         context information in this TCB and can consult processor resources
+ *         (page tables or TLBs or ???) to determine if the fill still needs
+ *         to be performed or not.
+ *
+ * Returned Value:
+ *   This function will return true if the mapping is in place and false
+ *   if the mapping is still needed.  Errors encountered should be
+ *   interpreted as fatal.
+ *
+ * Assumptions:
+ *   - This function is called from the normal tasking context (but with
+ *     interrupts disabled).  The implementation must take whatever actions
+ *     are necessary to assure that the operation is safe within this
+ *     context.
+ *
+ ****************************************************************************/
+
+bool up_checkmapping(FAR _TCB *tcb)
+{
+# warning "Not implemented"
+  return false;
+}
+
+#endif /* CONFIG_PAGING */
diff --git a/nuttx/arch/arm/src/arm/up_pginitialize.c b/nuttx/arch/arm/src/arm/up_pginitialize.c
new file mode 100755
index 000000000..7c6268217
--- /dev/null
+++ b/nuttx/arch/arm/src/arm/up_pginitialize.c
@@ -0,0 +1,92 @@
+/****************************************************************************
+ * arch/arm/src/arm/up_pginitialize.c
+ * Initialize the MMU for on-demand paging support.
+ *
+ *   Copyright (C) 2010 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 <debug.h>
+
+#include <nuttx/sched.h>
+#include <nuttx/page.h>
+
+#include "up_internal.h"
+
+#ifdef CONFIG_PAGING
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_pginitialize()
+ *
+ * Description:
+ *  Initialize the MMU for on-demand paging support..
+ *
+ * Input Parameters:
+ *   None.
+ *
+ * Returned Value:
+ *   None.  This function will crash if any errors are detected during MMU
+ *   initialization
+ *
+ * Assumptions:
+ *   - Called early in the platform initializatin sequence so that no special
+ *     concurrency protection is required.
+ *
+ ****************************************************************************/
+
+void up_pginitialize(void)
+{
+# warning "Not implemented"
+}
+
+#endif /* CONFIG_PAGING */
diff --git a/nuttx/arch/arm/src/common/up_internal.h b/nuttx/arch/arm/src/common/up_internal.h
index bff20e8b3..d8928a428 100644
--- a/nuttx/arch/arm/src/common/up_internal.h
+++ b/nuttx/arch/arm/src/common/up_internal.h
@@ -177,20 +177,26 @@ extern void up_puts(const char *str);
 extern void up_lowputs(const char *str);
 
 #ifdef CONFIG_ARCH_CORTEXM3
+
 extern uint32_t *up_doirq(int irq, uint32_t *regs);
 extern int  up_svcall(int irq, FAR void *context);
 extern int  up_hardfault(int irq, FAR void *context);
-#else
+
+#else /* CONFIG_ARCH_CORTEXM3 */
+
 extern void up_doirq(int irq, uint32_t *regs);
 #ifdef CONFIG_PAGING
+extern void up_pginitialize(void);
 extern void up_dataabort(uint32_t *regs, uint32_t far, uint32_t fsr);
-#else
+#else /* CONFIG_PAGING */
+# define up_pginitialize()
 extern void up_dataabort(uint32_t *regs);
-#endif
+#endif /* CONFIG_PAGING */
 extern void up_prefetchabort(uint32_t *regs);
 extern void up_syscall(uint32_t *regs);
 extern void up_undefinedinsn(uint32_t *regs);
-#endif
+
+#endif /* CONFIG_ARCH_CORTEXM3 */
 
 /* Defined in up_vectors.S */
 
diff --git a/nuttx/arch/arm/src/lpc313x/Make.defs b/nuttx/arch/arm/src/lpc313x/Make.defs
index 799984b07..66435f5b8 100755
--- a/nuttx/arch/arm/src/lpc313x/Make.defs
+++ b/nuttx/arch/arm/src/lpc313x/Make.defs
@@ -46,6 +46,10 @@ CMN_CSRCS	= up_assert.c up_blocktask.c up_copystate.c up_createstack.c \
 		  up_sigdeliver.c up_syscall.c up_unblocktask.c \
 		  up_undefinedinsn.c up_usestack.c
 
+ifeq ($(CONFIG_PAGING),y)
+CMN_CSRCS	+= up_pginitialize.c up_checkpaging.c up_allocpage.c
+endif
+
 CGU_ASRCS	= 
 CGU_CSRCS	= lpc313x_bcrndx.c lpc313x_clkdomain.c lpc313x_clkexten.c \
 		  lpc313x_clkfreq.c lpc313x_clkinit.c lpc313x_defclk.c \
diff --git a/nuttx/configs/ea3131/src/Makefile b/nuttx/configs/ea3131/src/Makefile
index 264b6902f..07443cc87 100755
--- a/nuttx/configs/ea3131/src/Makefile
+++ b/nuttx/configs/ea3131/src/Makefile
@@ -44,6 +44,9 @@ CSRCS		= up_boot.c up_buttons.c up_clkinit.c up_leds.c up_mem.c up_spi.c
 ifeq ($(CONFIG_EXAMPLES_NSH_ARCHINIT),y)
 CSRCS		+= up_nsh.c
 endif
+ifeq ($(CONFIG_PAGING),y)
+CSRCS		+= up_fillpage.c
+endif
 ifeq ($(CONFIG_EXAMPLE),usbstorage)
 CSRCS		+= up_usbstrg.c
 endif
diff --git a/nuttx/configs/ea3131/src/up_fillpage.c b/nuttx/configs/ea3131/src/up_fillpage.c
new file mode 100755
index 000000000..f72b88ec9
--- /dev/null
+++ b/nuttx/configs/ea3131/src/up_fillpage.c
@@ -0,0 +1,125 @@
+/****************************************************************************
+ * configs/ea3131/src/up_fillpage.c
+ * arch/arm/src/board/up_fillpage.c
+ *
+ *   Copyright (C) 2010 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 <debug.h>
+
+#include <arch/nuttx/sched.h>
+#include <arch/nuttx/page.h>
+
+#ifdef CONFIG_PAGING
+
+/****************************************************************************
+ * Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+ /****************************************************************************
+ * Name: up_fillpage()
+ *
+ * Description:
+ *  After a page is allocated and mapped by up_allocpage(), the actual
+ *  filling of the page with data from the non-volatile, must be performed
+ *  by a separate call to the architecture-specific function, up_fillpage().
+ *  This function is non-blocking, it will start an asynchronous page fill.
+ *  The common paging logic will provide a callback function, pg_callback,
+ *  that will be called when the page fill is finished (or an error occurs).
+ *  This callback is assumed to occur from an interrupt level when the
+ *  device driver completes the fill operation.
+ *
+ *  NOTE: Allocating and filling a page is a two step process.  up_allocpage()
+ *  allocates the page, and up_fillpage() fills it with data from some non-
+ *  volatile storage device.  This distinction is made because up_allocpage()
+ *  can probably be implemented in board-independent logic whereas up_fillpage()
+ *  probably must be implemented as board-specific logic.
+ *
+ * Input Parameters:
+ *   tcb - A reference to the task control block of the task that needs to
+ *         have a page fill.  Architecture-specific logic can retrieve page
+ *         fault information from the architecture-specific context
+ *         information in this TCB to perform the fill.
+ *   pg_callbck - The function to be called when the page fill is complete.
+ *
+ * Returned Value:
+ *   This function will return zero (OK) if the page fill was successfully
+ *   started (the result of the page fill is passed to the callback function
+ *   as the result argument).  A negated errno value may be returned if an
+ *   error occurs.  All errors, however, are fatal.
+ *
+ *   NOTE: -EBUSY has a special meaning. It is used internally to mean that
+ *   the callback function has not executed.  Therefore, -EBUSY should
+ *   never be provided in the result argument of pg_callback.
+ *
+ * Assumptions:
+ *   - This function is called from the normal tasking context (but
+ *     interrupts siabled).  The implementation must take whatever actions
+ *     are necessary to assure that the operation is safe within this context.
+ *   - Upon return, the caller will sleep waiting for the page fill callback
+ *     to occur.  The callback function will perform the wakeup.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_PAGING_BLOCKINGFILL
+int up_fillpage(FAR _TCB *tcb, FAR void *vpage)
+{
+# warning "Not implemented"
+  return -ENOSYS;
+}
+#else
+int up_fillpage(FAR _TCB *tcb, FAR void *vpage, up_pgcallback_t pg_callback)
+{
+# warning "Not implemented"
+  return -ENOSYS;
+}
+#endif
+
+#endif /* CONFIG_PAGING */
diff --git a/nuttx/include/nuttx/page.h b/nuttx/include/nuttx/page.h
index 1e5ed4449..a279dcc47 100755
--- a/nuttx/include/nuttx/page.h
+++ b/nuttx/include/nuttx/page.h
@@ -184,7 +184,6 @@ EXTERN void pg_miss(void);
  * Name: up_checkmapping()
  *
  * Description:
- *   
  *  The function up_checkmapping() returns an indication if the page fill
  *  still needs to performed or not. In certain conditions, the page fault
  *  may occur on several threads and be queued multiple times. This function
@@ -226,10 +225,16 @@ EXTERN bool up_checkmapping(FAR _TCB *tcb);
  *  The size of the underlying physical page is determined by the
  *  configuration setting CONFIG_PAGING_PAGESIZE.
  *
- *  NOTE:  This function must always return a page allocation. If all
+ *  NOTE 1: This function must always return a page allocation. If all
  *  available pages are in-use (the typical case), then this function will
  *  select a page in-use, un-map it, and make it available.
  *
+ *  NOTE 2: Allocating and filling a page is a two step process.  up_allocpage()
+ *  allocates the page, and up_fillpage() fills it with data from some non-
+ *  volatile storage device.  This distinction is made because up_allocpage()
+ *  can probably be implemented in board-independent logic whereas up_fillpage()
+ *  probably must be implemented as board-specific logic.
+ *
  * Input Parameters:
  *   tcb - A reference to the task control block of the task that needs to
  *         have a page fill.  Architecture-specific logic can retrieve page
@@ -264,6 +269,12 @@ EXTERN int up_allocpage(FAR _TCB *tcb, FAR void **vpage);
  *  This callback is assumed to occur from an interrupt level when the
  *  device driver completes the fill operation.
  *
+ *  NOTE: Allocating and filling a page is a two step process.  up_allocpage()
+ *  allocates the page, and up_fillpage() fills it with data from some non-
+ *  volatile storage device.  This distinction is made because up_allocpage()
+ *  can probably be implemented in board-independent logic whereas up_fillpage()
+ *  probably must be implemented as board-specific logic.
+ *
  * Input Parameters:
  *   tcb - A reference to the task control block of the task that needs to
  *         have a page fill.  Architecture-specific logic can retrieve page