How to deal with a long time's Clock drift?

[mahone]

Hi,

I use to the nrf51422 with nordic's dev/ev kit.I want to build a project and the purpose is to get the sensor's date and use the ant protocol to deliver the date to another chip every 5 hours.The rest of the time the chip will go to sleep.But recently I test two board's clock drift,I find the clock will drift 1s every 10min.And my test is simple,I use the way: while(1) {
nrf_gpio_pin_set(Pin); nrf_delay_ms(1000); nrf_gpio_pin_clear(Pin); nrf_delay_ms(1000); } I don't know is there any solution can solve this problem? Thanks!

[Mike]

I'm not sure if I understood what you want to do. But I'll try to give you some hints. Correct me if I got you wrong. If you want your device to have accurate real world time and date (like 2014/04/04 - 10:25:58) than the easiest way is too use an external RTC chip (example, there are many other manufacturers: para.maximintegrated.com/search.mvp that counts the time for you. You can read the time and date from it over an SPI or I2C interface depending of the chip you choose.

The advantage is that you can really go to sleep with your nrf51422 because the RTC chip will do everything for you. On some RTC chips you can even set an one time alarm or a periodic alarm so the RTC chip will wake the nrf51422 up by triggering in interrupt on the GPIO.

If you want to use just nRF51422 internals to implement this you could use the RTC that is in the chip. But there are some disadvantages:

• The internal RTCs (there are two: RTC0 and RTC1) do not have date and time. It's just a 24 bit counter, you need some extra software that will make a time from and date from that.
• One of the internal RTCs is used by the softdevice so you cannot use it from your application.
• The other internal RTC is used by the app_timer.c library. You can decide not to use the app_timer.c lib so the RTC is yours. But a lot of the examples use the app_timer.c and it's actually a very useful feature that might help you develop your application.

That the experience I made while trying to implement something similar. Hope that helps you.

[mahone]

Hi Mike, Thank you for your reply,That's a good idea but there may be a little disadvantages cause using an external RTC chip(I don't know how much it is) will need external power and external money consume.I want to make a BLE project,so every costs is counted.So it is best to solve it from software or maybe add a crystal or something like that.