Implements support for smaller interrupt tables as described at http://www.nuttx.org/doku.php?id=wiki:howtos:smallvectors . This is largely the work of Mark Schulte. However, I have made several changes to match with the Wiki document. If you like the change, thanks go to Marc. For any errors you can blame me.

arch/Kconfig

@@ -621,6 +621,44 @@ config ARCH_RAMVECTORS
 		If ARCH_RAMVECTORS is defined, then the architecture will support
 		modifiable vectors in a RAM-based vector table.
 
+config ARCH_MINIMAL_VECTORTABLE
+	bool "Minimal RAM usage for vector table"
+	default n
+	---help---
+		Use a minimum amount of RAM for the vector table.
+
+		Instead of allowing irq_attach() to work for all interrupt vectors,
+		restrict to only working for a select few (defined in your board
+		configuration). This can dramatically reduce the amount of RAM used
+		be your vector table.
+
+		To use this setting, you must have a file in your board config that
+		provides:
+
+		  #include <nuttx/arch.h>
+		  const irq_t g_irqmap[NR_IRQS] =
+		  {
+		    ... IRQ to index mapping values ...
+		  };
+
+		This table is index by the hardware IRQ number and provides a value
+		in the range of 0 to CONFIG_ARCH_NUSER_INTERRUPTS that the new,
+		mapped index into the vector table.  Unused, unmapped interrupts
+		should be set to (irq_t)-1.  So, for example, if g_irqmap[37] == 24,
+		Then the hardware interrupt vector 37 will be mapped to the interrupt
+		vector table at index 24.  if g_irqmap[42] == (irq_t)-1, then hardware
+		interrupt vector 42 is not used and if it occurs will result in an
+		unexpected interrupt crash.
+
+config ARCH_NUSER_INTERRUPTS
+	int "Number of interrupts"
+	default 0
+	depends on ARCH_MINIMAL_VECTORTABLE
+	---help---
+		If CONFIG_ARCH_MINIMAL_VECTORTABLE is defined, then this setting
+		defines the actual number of valid, mapped interrupts in g_irqmap.
+		This number will be the new size of the OS vector table
+
 comment "Board Settings"
 
 config BOARD_LOOPSPERMSEC