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Date: Mon, 04 Jul 2011 17:06:54 +0200
From: Fabien Chouteau <chouteau@adacore.com>
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Subject: Re: [Qemu-devel] [PATCH V2] [PowerPC][RFC] booke timers
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To: Scott Wood <scottwood@freescale.com>
Cc: qemu-devel@nongnu.org

On 01/07/2011 22:22, Scott Wood wrote:
> On Fri, 1 Jul 2011 16:13:41 +0200
> Fabien Chouteau <chouteau@adacore.com> wrote:
>> +static void booke_update_fixed_timer(CPUState         *env,
>> +                                     uint8_t           target_bit,
>> +                                     uint64_t          *next,
>> +                                     struct QEMUTimer *timer)
>> +{
>> +    ppc_tb_t *tb_env = env->tb_env;
>> +    uint64_t lapse;
>> +    uint64_t tb;
>> +    uint64_t period = 1 << (target_bit + 1);
>> +    uint64_t now;
>> +
>> +    now = qemu_get_clock_ns(vm_clock);
>> +    tb  = cpu_ppc_get_tb(tb_env, now, tb_env->tb_offset);
>> +
>> +    if (tb <= (1 << target_bit)) {
>> +        lapse = (1 << target_bit) - tb;
>> +    } else {
>> +        lapse = period - ((tb - (1 << target_bit)) % period);
> 
> We know period is a power of two, so just do "& (period - 1)".
> 
> That should let you get rid of the special case for
> "tb <= (1 << target_bit)" as well.
> 

Do you mean "lapse = period - ((tb - (1 << target_bit)) & (period - 1));" ?

I don't see how this solves the "tb <= (1 << target_bit)" case.

-- 
Fabien Chouteau