Setting Time From PSP

[jeffstjean]

I have a cFS bundle targeting a Linux environment. I have a cFS app that interfaces with some hardware to read time from an external GPS and the GPS' PPS is connected to the device. I'm a little confused about the correct way to configure time services to support this setup. My current plan is to:

1. Set CFE_PLATFORM_TIME_CFG_SERVER to true
2. Set CFE_PLATFORM_TIME_CFG_SOURCE to true
3. Set CFE_PLATFORM_TIME_CFG_SRC_GPS to true
4. Call CFE_TIME_ExternalTone() when a PPS signal is received
5. Call CFE_TIME_ExternalGPS() after the PPS is received with the time from the GPS

Is this the correct configuration?

Also, I have been supporting a local ("native") build where there is no PPS signal but the cFS app that reads the GPS can still read the time from a simulated hardware app running in parallel. To achieve this, I have the normal pc-linux PSP and a similar but modified hw-linux PSP where the platform-specific PPS code can be called.

For the hw-linux build, I can was planning on calling CFE_TIME_ExternalTone() from the PPS handler in the PSP and calling CFE_TIME_ExternalMET from the hardware cFS app. For the pc-linux build, to keep things similar to the hw-linux build, I was planning on using a 1Hz timer in the pc-linux PSP impl to call CFE_TIME_ExternalTone() and then immediately call CFE_TIME_ExternalMET with the local operating system time.

The major issue I see here is that the PSP obviously does not have visibility into the cFE - as it shouldn't. So, this is making me take a step back and evaluate if this is even the right path forward or if there's an easier way to accomplish this?

Edit: I'm also realizing that I could just handle a lot of this in the cFS hardware app. If I exposed some functionality in the PSP such that apps can register a callback for PPS signals then the hardware app can handling the tone and setting the time. The hw-linux PSP can call the callback when a PPS is received and the pc-linux can call it when its local timer expires.

[jeffstjean]

Just coming back on this as I came across a solution that appears to be working as expected.

I ended up writing a PPS API in the PSP to allow applications to register a callback to be invoked when the PPS is detected. It means that all platforms must exposes some PPS functionality but that works for my use-case. I then had my hardware-specific app make the call to CFE_TIME_ExternalTone() and set a flag for the main thread of the app to use CFE_TIME_ExternalMET() to send the time soon after the tone is sent.

This worked quite well until I realized scheduler (SCH rc-2.2.2) wasn't working as expected. This was tough to diagnose because SCH would throw errors about a noisy major frame, leading me to think it was an issue with how I was triggering the tone and time at tone. Turns out, there is a bug in SCH's minor frame callback. I didn't need all the complexity of the minor framing so I used @jphickey's gist showcasing some simplified SCH logic.

With that, I was successfully able to synchronize cFE time services with my external hardware. I haven't looked too much into the effects of using this simplified SCH logic but, from a first glance, it seems as though it fits my needs.

[RichLandau]

Thank you for the update. Part of the issue is that the open source SCH app hasn't been updated in some time due to some processes on our end. We're working to try to get it updated with numerous changes we have made internally and can revisit the issue after we get that through.