I received my RAK19007 base board, RAK4631 core, and RAK12501 GPS module to start a personal project of mine. Initial testing has gone great and I’m parsing the NMEA messages fine to write over serial and I decided some benchmarking was in order. Interested in testing the cold/warm/hot start claims from the product page, I tried understanding the schematics to see how to put it into standby. That’s when I realized, it does not appear we’re capable of doing so.
If I understand the schematics correctly, standby is paired with the reset so when I pull P1_02 I’m completely killing the power to the module, no? A critical reason I chose this module was to be capable of putting it into standby with decent cold and warm start times (my aim is to hold it in standby for a while and only bring it back to keep the almanac or ephemeris valid, depending on how frequent I want it to wake). My assumption appears correct in benchmarking, where my TTF averages 20 seconds with best cases being barely under the claimed <15 cold start and worst cases being well into the 30s. The chip manufacturer being used only claims <30 cold start, so why does RAK advertise better?
The module can be put in low power mode by switching of 3V3_S (through WB_IO2). The last location will still be available on next power up because the V_BCKP is always powered through 3V3.
My testing when pulling that low is that it appears to lose its RAM and takes just as long to get a fix no matter what. I will attempt to get a voltage off of V_BCKP in the process to see.
I believe you got a fast cold start. Neither your docs or manufacturer specifications document a warm start, and within 300 seconds you should have gotten a <2 second hot start (I don’t see how you would’ve had an invalid ephemeris that fast unless you were unlucky), which seems to prove what I believe is the case? I’ve also had sub-15 second cold starts every now and then.
