nios custom ip interrupt questions.

hi, everyone, i am new to nios and i have some questions about coustom ip interrupt.

my nios' frequence is 100MHz, in my custom ip, i creat a irq signal that last for 10 clk periods, in debug mode, the interrupt failed, the code can not go into the interrupt handler. then i change the irq signal, make it last 128 clk periods, then the interrupt works.

i have some questions:

1. how long should the irq signal last?

2. how the irq works, edge trigger or level trigger?

if it is edge trigger, why my interrupt failed if it only last for 10 clk periods?

if it is level trigger, my irq signal last 127 clk periods, will it cause another interrupt before my interrupt handler finish?

thanks