On Wed, 18 Apr 2001, Gabriel Paubert wrote: > On Wed, 18 Apr 2001, Grant Erickson wrote: > > >From the looks of drivers/char/rtc.c it would appear that this kernel > > driver only supports bus-attached RTCs such as the mentioned MC146818. Is > > this correct? > > I think so. > > > What is the correct access method / kernel tie-in for supporting such an > > I2C-based RTC device using the "standard" interfaces? > > Adding a new kind of clock to the kernel and setting the correct pointers > in ppc_md seems the right (if not necessarily simple) solution to your > problem.
As per Wolfgang's follow-on comments, it looks like there are actually two places I need to connect things. First, /dev/rtc such that 'hwclock' can get into the game. Second, the ppc_md interfaces, presumably so when either ntpd is running or the user does 'date MMDD...' both the Linux notion of time and the RTC get updated. > I wonder how you calibrate the decrementer frequency on this machine... As far as I can see, the decrementer frequency is set based on the 405GPs 64-bit decrementer. > ...I2C is too slow to get any precision, unless you accept to wait for > one minute or so at boot. I still have problems of reproducibility of > clock frequency measurements with bus attached RTC (on machines on > which the RTC is the only moderately precise timing source and its > interrupt line is unfortunately not connected). In light of this, after looking at the PPC kernel code again, it looks like I might NOT want to set get_rtc_time but just set_rtc_time to get the ntpd/date functionality. Thanks for the feedback. Regards, Grant Erickson -- Grant Erickson University of Minnesota Alumni o mail:erick205 at umn.edu 1996 BSEE o http://www.umn.edu/~erick205 1998 MSEE ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
