HI all!
I'm learning to write a timer interrupt handler by my own on
mips32(xls416 with 32bits cross compiled) , but to find that, eret
failed to quit.
detail:
I took the following steps:
1) copy exception vector to the physical address 0x180, then set ebase with it.
that is , memcpy these three instructions to 0x80000180,with
size 0x80 bytes:
lui k1, HIGH(handle_int)
addiu k1, k1, LOW(handle_int)
jr k1
2) this is handle_int , which is the entry of interrupts
LEAF(handle_int)
nop
la t9,do_IRQ
nop
jalr t9
nop
eret
nop
END(handle_int)
ps:
'nop' is used to avoid delay slot, and I did not add 'SAVE_ALL' or
'RESTORE_ALL' in handle_int, because it is just a demo, I want the
interrupt return
immediately.
3) this is do_IRQ
void do_IRQ(void)
{
ack_irq(); /* ack with compare register ,which is used to
generate timer interrupt*/
print("do_irq enter\n");
}
4) there is a main loop like this:
void main_loop()
{
local_irq_enable(); /* enable timer interrupt*/
while(1)
{
print("loop...\n");
}
}
I found that , the message in do_IRQ prints every 4s (I' ve set
timer of 4 seconds), however, the message in main_loop did not appear
q1: does that mean, the timer interrupt has never quit to main_loop ,
but a nested interrupt?
q2: that is to say, eret in handle_int failed to quit to main_loop?
q3: why this happend?
Thank you !
