I am planning to design my own custom base board for Col VF61 which will run Angstrom. My application requires the use of time including milliseconds. Currently I have Iris Carrier board which has the option of CMOS battery to save the values of time when the power is turned off. But I am confused, angstrom takes time from its own kernel time or from the external RTC in iris board.
If it is fetching time from external RTC which is M41T0M6 then how it is calculating time in milliseconds. In my base board if I use external RTC, then do I have to do I2C communication to use the time or is it possible to use linux own time and just use CMOS battery. Please help.
Please read about RTC and systemtime on the developer website here. Also the linux man page which discusses time might be helpful. Note that all SoC’s used on our modules provide high resolution timers.
During the times your system is switched off the RTC keeps counting the time. During boot the systemtime is initialized from the RTC with a second resolution.
Once the system is booted you’re applications use the systemtime with a much better resolution than milliseconds. This is the time which is used with the system interface referenced in the time man page.
If you would need millisecond resolution to measure time across reboots you will need some other form of time keeping device than the RTC.
As a complement or replacement of the RTC time can also be acquired with the NTP protocol from a timeserver on the network.