Trouble of NIOS2's timer interrupt

HI everyone

i have purchased the NIOS2 evaluate board--EP1C12 from the Altera. and i program a timer interrupt routine to create a square wave based on the evaluate board's standard design. my routines is below:# include "system.h"# include "sys/alt_irq.h"# include "altera_avalon_pio_regs.h"# include "altera_avalon_timer_regs.h"# include "alt_types.h"

alt_u8 x = 0x55;

static void timer_interrupts(void* context, alt_u32 id)

{

IOWR_ALTERA_AVALON_TIMER_STATUS(SYS_CLOCK_TIMER_BASE, 0);

x = x ^ 0xFF;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, x);

}

int main()

{

alt_irq_register(SYS_CLOCK_TIMER_IRQ, 0, timer_interrupts);

IOWR_ALTERA_AVALON_TIMER_PERIODL(SYS_CLOCK_TIMER_BASE, 0x1F40);// timer interrupt period is 100us

IOWR_ALTERA_AVALON_TIMER_PERIODH(SYS_CLOCK_TIMER_BASE, 0x00);

IOWR_ALTERA_AVALON_TIMER_CONTROL(SYS_CLOCK_TIMER_BASE, 7);

while(1)

{

;

}

}

i download the routine into the evaluate board and run it, then the square wave's period is 200us as designed. when i add some float calculation in the ISR, the period changed and bacame more than designed. the ISR is below:

static void timer_interrupts(void* context, alt_u32 id)

{

float i;

IOWR_ALTERA_AVALON_TIMER_STATUS(SYS_CLOCK_TIMER_BASE, 0);

x = x ^ 0xFF;

for(i=0;i<100;i++);

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, x);

}

The period is 2.784ms!!!!!!

If "float" became "alt_u8", the period is 200us as designed.

static void timer_interrupts(void* context, alt_u32 id)

{

alt_u8 i;

IOWR_ALTERA_AVALON_TIMER_STATUS(SYS_CLOCK_TIMER_BASE, 0);

x = x ^ 0xFF;

for(i=0;i<100;i++);

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, x);

}

I wonder if there can not be float calculation in the timer interrupt or the float calculation is very slow in NIOS2????