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Re: [Qemu-devel] [PATCH v3 5/9] openrisc: remove muldiv64()
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [PATCH v3 5/9] openrisc: remove muldiv64() |
Date: |
Tue, 8 Sep 2015 14:54:19 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
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);
> }
>
>
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