Improve Cortex-A5 context switching so that a little less copying is done

configs/sama5d3x-ek/ostest/defconfig

@@ -93,6 +93,8 @@ CONFIG_ARCH_CHIP="sama5"
 CONFIG_ARCH_HAVE_FPU=y
 CONFIG_ARCH_FPU=y
 # CONFIG_ARCH_HAVE_MPU is not set
+CONFIG_ARCH_HAVE_LOWVECTORS=y
+CONFIG_ARCH_LOWVECTORS=y
 CONFIG_PGTABLE_VADDR=0x20000000
 # CONFIG_ARCH_ROMPGTABLE is not set
 # CONFIG_PAGING is not set

configs/sama5d3x-ek/scripts/ddram.ld

@@ -36,11 +36,14 @@
 /* The SAMA5D3 has 128 KB of ISRAM beginning at virtual address 0x0030:0000.
  * This memory configuration, however, loads into the 64 MB SDRAM on board
  * the SAMA5D3x-EK which lies at 0x2000:0000
+ *
+ * Vectors in low memory are assumed and 16KB of ISRAM is reserved at the
+ * high end of ISRAM for the page table.
  */
 
 MEMORY
 {
-	isram (W!RX) : ORIGIN = 0x300000, LENGTH = 128K
+	isram (W!RX) : ORIGIN = 0x300000, LENGTH = 128K - 16K
 	sdram (W!RX) : ORIGIN = 0x20000000, LENGTH = 64M
 }
 

configs/sama5d3x-ek/scripts/isram.ld

@@ -33,11 +33,15 @@
  *
  ****************************************************************************/
 
-/* The SAMA5D3 has 128 KB of ISRAM beginning at virtual address 0x0030:0000. */
+/* The SAMA5D3 has 128 KB of ISRAM beginning at virtual address 0x0030:0000.
+ *
+ * Vectors in low memory are assumed and 16KB of ISRAM is reserved at the
+ * high end of ISRAM for the page table.
+ */
 
 MEMORY
 {
-	isram (W!RX) : ORIGIN = 0x300000, LENGTH = 128K
+	isram (W!RX) : ORIGIN = 0x300000, LENGTH = 128K - 16K
 }
 
 OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")

configs/sama5d3x-ek/scripts/pg-sram.ld

@@ -60,6 +60,9 @@
  * get a link time error saying that the locked region is full, you may have to
  * re-organize this memory layout (here and in defconfig) to make the locked
  * region even bigger.
+ *
+ * NOTE 3: Vectors in low memory are assumed and 16KB of ISRAM is reserved at
+ * the high end of ISRAM for the page table (?).
  */
 
 MEMORY