#include #include #include #include .text .set mips1 .set reorder .set macro .set noat .align 5 # MIPS has 16 exception vectors numbered 0 to 15 # vector number 0 is for interrupts and the others are for various exceptions # The following code is installed as the handler for exception 0 # There are 8 possible interrupts that can cause this exception. # The cause register indicates which are pending # The status register indicates which are enabled # This code segment basically will decipher which interrup occurred (7 downto 0) # and pass an integer indicating which was the highest priority pending interrupt # to the do_IRQ routine. NESTED(hpIRQ, PT_SIZE, sp) SAVE_ALL CLI # Important: mark KERNEL mode ! /* * Get pending interrupts */ mfc0 t0,CP0_CAUSE # get pending interrupts mfc0 t1,CP0_STATUS # get enabled interrupts and t0,t1 # isolate allowed ones andi t0,0xff00 # isolate pending bits sll t0,16 # shift the pending bits down beqz t0,3f # no pending intrs, then spurious nop # delay slot /* * Find irq with highest priority * FIXME: This is slow - use binary search */ la a0,7 1: bltz t0,2f # found pending irq subu a0,1 sll t0,1 b 1b nop # delay slot call_do_IRQ: 2: move a1,sp jal do_IRQ nop # delay slot j ret_from_irq nop /* mfc0 t0,CP0_STATUS # disable interrupts ori t0,1 xori t0,1 mtc0 t0,CP0_STATUS la a1, ret_from_irq jr a1 */ 3: j spurious_interrupt END(hpIRQ)