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User avatar
By naltieri
#220132
Assuming the RTC of the Artemis Open log has been synchronized to GPS when the board is first powered up, then GPS board is disabled, then using pin 11 as a trigger input to the open log board applying a 2 Volt rising edge, what is maximum permitted trigger rate that the Artemis Open log can trigger and time stamp date and time.
Hopping the trigger input can cope with a trigger rate of several hundred Hz ?
Assuming all onboard sensors are disabled, serial logging is disable, analog logging is disabled and I only wish to record the absolute date and time when pin 11 is triggered by a rising edge.
Not sure what the timing drift is on the RTC but if the board is powered by an external battery figured the RTC should remain precise for a long time as long as the battery is topped up from a USB charger.
Thanks.
User avatar
By PaulZC
#220133
Hi Nick,
You are entering unchartered territory! In theory, you should be able to achieve the same maximum rate as what the OLA achieves when logging "freely". The interrupt code is very efficient and should not slow down the logging rate at all. Please test it and let us know what you find.
Best wishes,
Paul
User avatar
By naltieri
#220137
Hi Paul,
Thanks, I'll see what I find out, once Iv'e done some tests. When the OLA is triggered using pin 11 and logs absolute time, what is minimum time format resolution can be achieved in its log, is it to just to nearest millisecond or lower resolution microsecond or even nanosecond. i.e. HR:MM:ss.SSSSSSSSS
Thanks,
User avatar
By naltieri
#220139
Apologies for confusion but think number format i.e. HR:MM:ss.SSSSSSSSS may be something different.
So more interested to know how many decimal places the time stamp data has. so if board is triggered at 10am , is it recorded as 10:00:00.000000000
i.e with 9 decimal places gives nano second resolution. But I can live with microsecond time stamp resolution.
User avatar
By PaulZC
#220160
Hi Nick,
This is going to be difficult to achieve...
The OLA code logs time from the internal Real Time Clock and that has a resolution of 0.01 seconds.
It would be straight forward to add a feature to let you log the microsecond count from the processor too BUT you need to be aware that that value will reset if the OLA goes into its low power mode. If you are logging continuously, then this should not be a problem for you.
Nanosecond resolution is not possible.
If this is something you need then please raise a "Feature Request" issue on GitHub:
https://github.com/sparkfun/OpenLog_Artemis/issues
Here is a recent example:
https://github.com/sparkfun/OpenLog_Artemis/issues/42
Best wishes,
Paul
User avatar
By naltieri
#220595
Hi Paul,
Was wondering whether it is possible to consider the feature request idea for a firmware update to the OLA to improve the precision of the triggered time stamp from its current 10ms down to mico second ideally or at least 10 microsecond.
Best regards, Nick
User avatar
By PaulZC
#220675
Hi Nick,
Don't worry - we haven't forgotten about your request. These things go in cycles. I'm working on other projects at the moment but will be revisiting the OLA in the next 1-2 weeks. Thank you for your patience.
Best wishes,
Paul
User avatar
By naltieri
#221205
Hi Paul,
Just tried out V 1.8, thats looking good, I was initially a little confused as the microseconds log appears as a separate column and not joined up with the milliseconds from the main time stamp. As the main time stamp has a resolution of 10milli second, am assuming the number on the left side of the microsecond log is 1 millisecond, the next number being 100 micro second resolution and so on. Would be great if the microsecond log count was joined up with the main time stamp time instead of being a separate column.
Best regards, Nick
User avatar
By naltieri
#221225
Noted one other observation that sometimes the log data for the microseconds can show a negative symbol before its number which I dont understand, seen this a couple of times, normally after enabling and disabling various logging options from the main menu, its micro log can get confused ?
User avatar
By PaulZC
#221374
Hi Nick,

Thank for spotting the negative micros issue. I will need to investigate that. I have opened an Issue here:
https://github.com/sparkfun/OpenLog_Artemis/issues/57

Re. 'linking' the RTC and micros timestamps: I really don't think it would be sensible to do that. The hours, minutes and seconds come from the Artemis' Real Time Clock, whereas the microseconds come from an internal counter. Micros will reset whenever the Artemis goes into deep sleep, whereas the RTC keeps going. Thus you would have discontinuities each time this happened. I'm afraid you will need to manually 'add' the two columns when you analyze your data.

Also, please be aware that micros uses a 32-bit unsigned integer and so it will wrap around to zero every 71.583 minutes.

Best wishes,

Paul
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