Add irqasm.S... still no interrupts, but no crashes either...

fw/irqasm.S

@@ -0,0 +1,53 @@
+#include "picorv32.h"
+
+	// The IRQ dispatch code is written in assembly to make
+	// better use of the register bank switching: can simply
+	// use the saved registers here, no saving needed.
+	// registers need to be 
+	.pushsection ".init.irq","ax"
+	.globl _irq
+_irq:
+	addqxi sp,sp,0
+	
+	// s10 contains the IRQ return address, s11 the mask of
+	// IRQs to be handled.
+	lui s0, %hi(__irq_handler_table)
+	li s1, 0
+.Lirq_loop:
+	// ctz would make this more efficient...
+	slli t0,s11,16
+	bnez t0,1f
+	srli s11,s11,16
+	addi s1,s1,16*4
+1:
+	zext.b t0,s11
+	bnez t0,2f
+	srli s11,s11,8
+	addi s1,s1,8*4
+2:
+	andi t0,s11,15
+	bnez t0,3f
+	srli s11,s11,4
+	addi s1,s1,4*4
+3:
+	andi t0,s11,3
+	bnez t0,4f
+	srli s11,s11,2
+	addi s1,s1,2*4
+4:
+	andi t0,s11,1
+	bnez t0,5f
+	srli s11,s11,1
+	addi s1,s1,1*4
+5:
+	add t0,s0,s1
+	lw t0,%lo(__irq_handler_table)(t0)
+	srli a0,s1,2
+	jalr t0
+	srli s11,s11,1
+	addi s1,s1,4*1
+	bnez s11,.Lirq_loop
+
+	mret
+	.type _irq, @function
+	.size _irq, . - _irq