On Wed, Sep 14, 2016 at 10:26:19PM +0200, Richard Cochran wrote: > On Wed, Sep 14, 2016 at 04:02:29PM +0300, Grygorii Strashko wrote: > > + clocks_calc_mult_shift(&mult, &shift, freq, NSEC_PER_SEC, maxsec); > > + > > + cpts->cc_mult = mult; > > + cpts->cc.mult = mult; > > In order to get good resolution on the frequency adjustment, we want > to keep 'mult' as large as possible. I don't see your code doing > this. We can rely on the watchdog reader (work queue) to prevent > overflows.
I took a closer look, and assuming cc.mask = 2^32 - 1, then using clocks_calc_mult_shift() produces good results for a reasonable range of input frequencies. Keeping 'maxsec' constant at 4 we have: | Freq. MHz | mult | shift | |-----------+------------+-------| | 100 | 0xa0000000 | 28 | | 250 | 0x80000000 | 29 | | 500 | 0x80000000 | 30 | | 1000 | 0x80000000 | 31 | Can the input clock be higher than 1 GHz? If not, I suggest using clocks_calc_mult_shift() with maxsec=4 and a setting the watchdog also to 4*HZ. Thanks, Richard
