Trent Piepho wrote: > The basic frequency calculation done in dvb-pll is to take the desired > frequency, add the IF frequency, and then divide by the reference > frequency. > > When dvb-pll does the division, it just rounds the result down. It would > make more sense to round to the nearest integer, which is done by adding > 1/2 the divisor (the reference frequency) before dividing. > > Some PLL definitions already do this, by adding one half the reference > frequency to the IF frequency. The effect is the same, except one looking > at the code doesn't know if they are seeing the IF frequency, or the IF > frequency plus 1/2 the reference frequency. Of course some PLL defintions > do it one way and some do it the other and there is no record of which is > which. > > I think it makes a lot more sense put just the IF frequency in the PLL > definition, and take care of rounding properly in the dvb-pll code. So I > have attached a patch which does this. In order to do this, I had to guess > which PLLs had stepsize/2 added to the offset and which didn't. > > The second patch moves the IF frequency out of the per-band data. There is > no reason for the IF to change from one band to another, and in all of the > PLLs defined the IF is constant across bands. > > As far as which PLLs had offsets with stepsize/2 added and which didn't, > I've made a list of all the IF frequencies defined in dvb-pll: > > dvb_pll_thomson_dtt7610 44 > dvb_pll_microtune_4042 44 > dvb_pll_thomson_dtt761x 44 > dvb_pll_lg_tdvs_h06xf 44 > dvb_pll_tdhu2 44 > dvb_pll_tuv1236d 44 > dvb_pll_samsung_tbmv 44 > dvb_pll_tua6010xs 36 1/8 > dvb_pll_thomson_dtt7579 36 1/6 > dvb_pll_tded4 36 1/6 > dvb_pll_tua6034 36 1/6 > dvb_pll_unknown_1 36 1/6 > dvb_pll_thomson_dtt759x 36 1/6 > dvb_pll_lg_z201 36 1/6 > dvb_pll_philips_td1316 36 1/6 (rounded to nearest kHz) > dvb_pll_tda665x 36 1/6 (rounded to nearest kHz) + step/2 > dvb_pll_fmd1216me 36 1/8 (rounded to two decimals) + step/2 > dvb_pll_thomson_fe6600 36 1/8 (rounded to two decimals) + step/2 > dvb_pll_env57h1xd5 36 1/8 + step > dvb_pll_philips_sd1878_tda8261 499 > > Anyway, from this list I think it's clear that the PLLs with a pre-adjusted > offset are dvb_pll_tda665x, dvb_pll_fmd1216me, dvb_pll_thomson_fe6600, and > dvb_pll_env57h1xd5. > > dvb_pll_philips_sd1878_tda8261 is an odd one, as it's the only satellite > PLL with zero-IF output in the list. It uses an offset of 499 with a > stepsize of 500 kHz so that it rounds _up_. I've left this PLL rounding > up, assuming there is a reason it was this way. > > Also, dvb_pll_env57h1xd5 is not 36 1/8 + step/2, but 36 1/8 + step. I > think this is a bug. If you go back to patch 1740 which created the > dvb-pll definition, you'll see it was taken from the dibusb driver. The > original code for this pll was: > > u32 freq_khz = fep->frequency / 1000; > u32 tfreq = ((freq_khz + 36125)*6 + 500) / 1000; > > If you multiple that out and reduce it, you get: > tfreq = (fep->frequency + 36125000 + 166667/2) / 166667; > > But the dvb-pll definition is using 36125000 + 166667. Trent, This looks good to me, pending review from the other dvb developers. Acked-by: Michael Krufky <mkrufky at linuxtv dot org> _______________________________________________ linux-dvb mailing list linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
