Re: [Xenomai-core] ns vs. tsc as internal timer base

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Philippe Gerum wrote:
 > static inline unsigned long long ns_2_cycles(unsigned long long ns)
 > {
 >      return ns * ns2cyc_scale >> NS2CYC_SCALE_FACTOR;

This multiplication is 64 bits * 32 bits, the intermediate result may
need more than 64 bits, so you should compute it the same way as the
beginning of ullimd. Something like:

static inline unsigned long long ns_2_cycles(unsigned long long ns)
{
    unsigned nsh, nsl, tlh, tll;
    unsigned long long th, tl;

    __rthal_u64tou32(ns, nsh, nsl);
    tl = rthal_ullmul(nsl, ns2cyc_scale);
    __rthal_u64tou32(tl, tlh, tll);
    th = rthal_ullmul(nsh, ns2cyc_scale);
    th += tlh;

    tll = (unsigned) th << (32 - NS2CYC_SCALE_FACTOR) | tll >> NS2CYC_SCALE_FACTOR;
    th >>= NS2CYC_SCALE_FACTOR;
    return __rthal_u64fromu32(th, tll);
}


-- 


					    Gilles Chanteperdrix.