questions about nios interrupts

hi everyone.

there are 2 interrupts in my project

interrupt A has lower poriority than interrupt B

i think if the interrupt B comes when the code is executing the interrupt A's handler, the code should go to the interrupt B's handler.the code return to the interrupt A's handler after finish the interrupt B's handler.

but in my project, in debug mode, i set a breakpoint at the begining of interrupt A's handler, i resume the code (F8), then i let interrupt A happen, so the code stop at the break point, then i let interrupt B happen, i press F5, let the code run single step, the code did not go to interrupt B's handler, and i find the code go to interrupt B's handler untill finish the interrupt A's handler.

why this happed?

# include "alt_types.h"# include "altera_avalon_pio_regs.h"# include "sys/alt_irq.h"# include "system.h"# include <stdio.h># include <unistd.h>

alt_u8 find_zero_counter=0;

alt_32 zero_position[255]={0};

void ft245_interrupt() //lower poriority interrupt

{

//

alt_u32 i=0;

alt_u16 j=0;

alt_u16 a=0;

i=alt_irq_enabled();//

j=IORD_16DIRECT(FT245_IRQ_1_0_BASE,0x0); //

a=(j|0x4000);

IOWR_16DIRECT(FT245_IRQ_1_0_BASE,0,0xc000); //clear interrupt

for(;;)

{

j=IORD_16DIRECT(FT245_IRQ_1_0_BASE,0x0);

if ((j&0xc000)==0) break;

}

IOWR_16DIRECT(FT245_IRQ_1_0_BASE,0,0x8000); //tell ft245_driver to read from ft245

}

void encoder_find_zero() //higher poriority interrupt

{

alt_u32 i=0;

alt_32 xifen=0,forward=0,backward=0;

i=alt_irq_enabled();//

IOWR_32DIRECT(INC_CALC_0_BASE,0,0xc0000000); // clear interrupt

while(1)

{

i=IORD_32DIRECT(INC_CALC_0_BASE,0);//

if ((i&0xf0000000)==0x0) break; //

}

IOWR_32DIRECT(INC_CALC_0_BASE,0,0x60000000); // prepare S_inc_xifen_at_zero_reg, S_inc_forward_at_zero_reg,S_inc_backward_at_zero_reg, return S_inc_xifen_at_zero_reg,nios should read after interrupt

while(1)

{

xifen=IORD_32DIRECT(INC_CALC_0_BASE,0);//

if ((xifen&0xf0000000)==0x0) break; //

if ((i&0xf0000000)==0xf0000000) break;//

}

}

int main()

{

alt_u32 i=0;

alt_u32 error_signal_address=0;

alt_u16 j=0;

alt_u32 moire_sin[256]={0};

alt_u32 moire_cos[256]={0};

alt_32 xifen=0,forward=0,backward=0,position=-5;

alt_u16 a=0;

i=alt_irq_enabled();

//register interrupt handler of lower poriority interrupt

alt_ic_isr_register (FT245_IRQ_1_0_IRQ_INTERRUPT_CONTROLLER_ID,

FT245_IRQ_1_0_IRQ,

ft245_interrupt,

NULL,

NULL);

//register interrupt handler of higher poriority interrupt

alt_ic_isr_register (INC_CALC_0_IRQ_INTERRUPT_CONTROLLER_ID,

INC_CALC_0_IRQ,

encoder_find_zero,

NULL,

NULL);

//enable interrupt

j=alt_ic_irq_enable(FT245_IRQ_1_0_IRQ_INTERRUPT_CONTROLLER_ID,FT245_IRQ_1_0_IRQ);//

j=alt_ic_irq_enable(INC_CALC_0_IRQ_INTERRUPT_CONTROLLER_ID,INC_CALC_0_IRQ);//

i=alt_irq_enabled();

IOWR_16DIRECT(FT245_IRQ_1_0_BASE,0,0x8000); //tell ft245_driver to read from ft245

while (1)

{

}

return 0;

}