Time spent in ticks...

[Sebastian Huber]

----- Am 13. Okt 2016 um 18:21 schrieb Jakob Viketoft jakob.viketoft at aacmicrotec.com:

[...]
> Even though _Watchdog_Tick() "only" takes ~100 us now, it still sound much
> higher than your total tick with a slower system (we're running at 50 MHz).
> 
> Is there anything we can do to improve these numbers? Is Clock_isr intended to
> be run uninterrupted as it is now? Can't see that much of the BSP patch code
> has anything to do with the speed of what I'm looking at right now...

It seems that the or1k has no support for add with carry? This makes basic 64-bit operations quite expensive. How fast are the shift instructions on your processor? Does it support 32-integer multiplication instructions?

On the soft-core Nios 2 processor you get for example (nios2-rtems4.12-gcc -O2 -mhw-mulx -mhw-mul -mhw-div):

uint64_t add(uint64_t a, uint64_t b)
{
  return a + b;
}

uint64_t mul(uint64_t a, uint64_t b)
{
  return a * b;
}

        .size   rs, .-rs
        .align  2
        .global add
        .type   add, @function
add:
        add     r2, r4, r6
        cmpltu  r4, r2, r4
        add     r3, r5, r7
        add     r3, r4, r3
        ret
        .size   add, .-add
        .align  2
        .global mul
        .type   mul, @function
mul:
        mul     r5, r5, r6
        mul     r7, r7, r4
        mulxuu  r3, r4, r6
        mul     r2, r4, r6
        add     r5, r5, r7
        add     r3, r5, r3
        ret
        .size   mul, .-mul