Am Freitag, 12. April 2019, 14:32:08 CEST schrieb Christoph Müllner: > > On 12.04.19 14:21, Heiko Stübner wrote: > > Hi Christoph, > > > > Am Freitag, 12. April 2019, 14:12:52 CEST schrieb Christoph Müllner: > >> On 12.04.19 13:52, Heiko Stübner wrote: > >>> Am Mittwoch, 3. April 2019, 11:42:24 CEST schrieb Elaine Zhang: > >>>> From: Finley Xiao <finley.xiao@xxxxxxxxxxxxxx> > >>>> > >>>> From Rockchips fractional divider usage, some clocks can be generated > >>>> by fractional divider, but the input clock frequency of fractional > >>>> divider should be less than a specified value. > >>>> > >>>> Signed-off-by: Finley Xiao <finley.xiao@xxxxxxxxxxxxxx> > >>>> Signed-off-by: Elaine Zhang <zhangqing@xxxxxxxxxxxxxx> > >>> > >>> can you tell me where these maximum input values come from? > >>> > >>> I talked to Christoph from Theobroma (Cc'ed) last week and he mentioned > >>> that they're using the fractional divider with a higher input frequency > >>> to create a very specific frequency [some details are gone from my memory > >>> though] they can't get otherwise. > >>> > >>> So I really don't want to break their working setup by introducing barriers > >>> that are not strictly necessary. > >>> > >>> @Christoph: can you describe the bits from your fractional setup that > >>> I've forgotten please? > >> > >> We need to set the I2S0 clock to 24.56 MHz. > >> > >> When restricting the input frequency to a maximum of 600 Mhz, > >> we could use the integer divider to get 400 Mhz (dividing by 2). > >> However, with the 400 Mhz as input to the frac divider, > >> we run into the problem, that the maximum possible output frequency > >> is 20 MHz (there is another restriction which states that the > >> fraction input : output frequency must be >= 20). > > > > just for clarification, what is the current input frequency you > > already use sucessfully? > > Our working setup uses the integer divider to reduce to 400 MHz > and uses the frac divider to get something near 24.56 MHz. > I have to admit I have never measured what's on the clock line. Ah ok, so the 600MHz input maximum is ok for your setup and the "< 20" ratio is the question. I thought I remembered you using a higher than 600MHz input rate. [bad memory on my side] _______________________________________________ Linux-rockchip mailing list Linux-rockchip@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-rockchip
