Re: [Qemu-devel] [PATCH v3 5/9] openrisc: remove muldiv64()

[Laurent Vivier]

ping ?

On 27/08/2015 21:33, Laurent Vivier wrote:
> Originally, timers were ticks based, and it made sense to
> add ticks to current time to know when to trigger an alarm.
> 
> But since commit:
> 
> 7447545 change all other clock references to use nanosecond resolution 
> accessors
> 
> All timers use nanoseconds and we need to convert ticks to nanoseconds, by
> doing something like:
> 
>     y = muldiv64(x, get_ticks_per_sec(), TIMER_FREQ)
> 
> where x is the number of device ticks and y the number of system ticks.
> 
> y is used as nanoseconds in timer functions,
> it works because 1 tick is 1 nanosecond.
> (get_ticks_per_sec() is 10^9)
> 
> But as openrisc timer frequency is 20 MHz, we can also do:
> 
>     y = x * 50; /* 20 MHz period is 50 ns */
> 
> Signed-off-by: Laurent Vivier <address@hidden>
> ---
>  hw/openrisc/cputimer.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/openrisc/cputimer.c b/hw/openrisc/cputimer.c
> index 9c54945..560cb91 100644
> --- a/hw/openrisc/cputimer.c
> +++ b/hw/openrisc/cputimer.c
> @@ -22,7 +22,7 @@
>  #include "hw/hw.h"
>  #include "qemu/timer.h"
>  
> -#define TIMER_FREQ    (20 * 1000 * 1000)    /* 20MHz */
> +#define TIMER_PERIOD 50 /* 50 ns period for 20 MHz timer */
>  
>  /* The time when TTCR changes */
>  static uint64_t last_clk;
> @@ -36,8 +36,7 @@ void cpu_openrisc_count_update(OpenRISCCPU *cpu)
>          return;
>      }
>      now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> -    cpu->env.ttcr += (uint32_t)muldiv64(now - last_clk, TIMER_FREQ,
> -                                        get_ticks_per_sec());
> +    cpu->env.ttcr += (uint32_t)((now - last_clk) / TIMER_PERIOD);
>      last_clk = now;
>  }
>  
> @@ -59,7 +58,7 @@ void cpu_openrisc_timer_update(OpenRISCCPU *cpu)
>      } else {
>          wait = (cpu->env.ttmr & TTMR_TP) - (cpu->env.ttcr & TTMR_TP);
>      }
> -    next = now + muldiv64(wait, get_ticks_per_sec(), TIMER_FREQ);
> +    next = now + (uint64_t)wait * TIMER_PERIOD;
>      timer_mod(cpu->env.timer, next);
>  }
>  
>