max80_fw/fw/irqasm.S

#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"
	.balign 4
	.globl _irq
	.option push
	.option norvc	// Alignment matters more here
_irq:
	addqxi sp,sp,0
	
	// s10 contains the IRQ return address, s11 the mask of
	// IRQs to be handled.
	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:
	// __irq_handler_table must be in the zero page
	// However, prevent the linker from incorrectly relaxing
	// this instruction.
	.option push
	.option norelax
	lw t0,%lo(__irq_handler_table)(s1)
	.option pop
	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
	.option pop