7 Replies Latest reply on Oct 22, 2015 9:08 AM by mikalhart

    Minimal Power On Requirements?


      In another thread (Divorce from Adapters: Taking the Custom "Block" Plunge), I alluded to this question, but let me say ask it directly here.  I want to see if I can understand the minimum requirements to get Edison to boot without either of the breakout boards.  The question is:


      • What is the minimal set of buses/signals that need to be manipulated to get Edison to boot from a 3.7V LiPo battery?


      Power rails

      Obviously, we need to connect the positive battery terminal to VSYS and the negative to GND.



      It's been recommended that we strap PWRBTN# to VSYS with a 10K resistor.  (Both the mini breakout and the SparkFun console block do this.)



      The breakout guide says

      • DCIN is a signal that indicates whether Edison is being powered from a battery or from an external power source. DCIN also sets the voltage level required on VSYS in order to boot. When DCIN is floating or tied to ground, the voltage on VSYS must rise from 2.5 to 3.5 V in 10 ms; otherwise the boot is aborted. When the boot is aborted, power must be cycled below 2.5 V. If DCIN is connected to VSYS, Edison will start to boot when VSYS is above 2.5 V for 100 ms.
      • Note:  When DCIN is connected to VSYS, boot will occur whenever the voltage is above 2.8 V for 100 ms. The DCIN signal is attached to VSYS on the PCB.


      I can't quite parse this.  How exactly does one tell the Edison that it's powered from battery?  Also it would seem that the "Note" completely overrides the bold sentence immediately prior.  What do we need to do with this DCIN signal?  Is this relevant to applications that don't use the breakouts?



      The mini-breakout board straps this to 1.8V via a 10K resistor, but I think this is just for the green "all's well" LED.  Do we have to do anything with this signal?




      Thank you,


      Mikal Hart

        • 1. Re: Minimal Power On Requirements?

          Hi mikalhart,


          Reading the Intel® Edison Compute Module Hardware Guide I understand you should connect VSYS to a 3.3V - 4.5V voltage source. Connect DCIN to VSYS. PWRBTN# is an input, and it should connect to VSYS in the same way showed in Intel® Edison Breakout Board Schematic (pdf), page 7. RESET_OUT# is an output to indicate a system reset.


          That is my interpretation about the info in the documentation, do you have the same interpretation or another one?




          • 2. Re: Minimal Power On Requirements?

            I think you just treat DCIN as a signal to tell Edison that there's a DC power supply connected.


            If you leave DCIN floating (I assume it's pulled down) and the voltage on Vsys is below 3.5V, it assumes that the battery attached to it is flat (3.5V with a small load is pretty much completely flat for a single LiPo cell) and aborts the boot sequence. Presumably if it doesn't rise from 2.5V to 3.5V in 10ms then that implies a substantial resistance in the supply wires, which is also a good reason to stop booting.


            If you tie DCIN high (ie to Vsys) then you're telling it "this is a power supply". This means that Edison doesn't care if the supply appears to be "flat", and it doesn't impose a limitation on the supply rise time (power supplies with big output capacitors can take a while to reach the right voltage).


            Having Vsys and DCIN separated by the power outputs is a bit annoying (hard to connect them together). I've ended up ignoring the Edison voltage outputs and putting my own 1.8V regulator elsewhere on the board.

            • 3. Re: Minimal Power On Requirements?

              Thank you, @Slayte and @Diego_Intel.  I'm starting to come around to understand that


              DCIN floating or low = "battery attached: don't boot if it's flat"

              DCIN pulled to VSYS = "Power supply attached or ignore battery".


              I sort of read the documents the same way.  But I have two problems with this (besides the fact that the documentation doesn't read very clear to me):


              1. I am tying DCIN to VSYS in the custom Edison "block" I mention in the other thread.  But my Edison doesn't seem to boot when I attach a fully charged battery.  This same Edison does boot when attached to either USB-powered breakout.  Perhaps there is something else wrong with my board.  I'll keep investigating.

              2. The SparkFun people seem to be tying DCIN to VSYS in all their blocks, including the "battery block".  If it's important to signal to Edison that there is a (possibly dying) battery attached, why don't the SparkFun people do it?


              What is the benefit of telling Edison "please don't boot if this battery is flat" anyway?

              • 4. Re: Minimal Power On Requirements?

                (1) That is very odd. I can't see any reason why a fully charged battery (I assume this is a 1S LiPo) wouldn't work when USB does. I assume you've connected the power/reset pins the same as on the Sparkfun boards?


                (2) For hobbyists it probably makes more sense to just boot regardless of the voltage and assume that the user knows what they're doing (some might be using LiFe batteries or a couple of NiMH ones). Better than dealing with all the support requests for "Edison won't boot" that turn out to be because the battery isn't a LiPo, or because they're just running it off a 3.3V power supply, etc. I guess there's a potential for problems to occur if it loses power during boot, but that could happen when run from a power supply too.


                I suspect that this is "the power management chip supports this feature so we might as well have a pin for it" more than anything else.

                • 5. Re: Minimal Power On Requirements?

                  Thanks Slatye.  I hope to get a pre-release SparkFun console block soon.  I'll use that to examine the boot spew (if any) and hopefully get to the root of the problem.


                  > I assume you've connected the power/reset pins the same...

                  Well, not the resetout# pin because DiegoV_Intel said that was an output-only pin?  I guess I'll try wiring it up like SparkFun does to see if it makes any difference.  Thanks!

                  • 6. Re: Minimal Power On Requirements?

                    Hi mikalhart,


                    Yes, the RESET_OUT# pin is an output pin to indicate a system reset. It can be used for example, to inform to an external hardware when the system reset occurs.




                    • 7. Re: Minimal Power On Requirements?

                      I just thought I'd make a happy update to this ancient post.


                      Just to recap, back in November I created my own Sparkfun-esque Edison GPS "block", but when I attached it to my Edison and applied power, it didn't boot.  So it sat on the shelf for 11 months.  Recently I got it back down and had a little "eureka!" moment.  I now know why it doesn't boot, and I have fixed it!


                      Here's what happened.  I had routed the GPS RX signals through UART2 a.k.a. /dev/ttyMFD2.  That's the serial port we know as the "console", or "kernel spew" port.  I was thinking that since the kernel spew goes in one direction (TX) and the GPS stream goes in the other (RX), I could use the same port for both.  The problem is that there's one point early in the boot process where it invites the user to "press any key to abort boot...", and of course the GPS stream triggers this boot abort.  I cut the UART2 traces to my board and reattached the GPS to UART1, and now it boots beautifully.  Very happy!


                      Many thanks to the Sparkfun "base" block for allowing me to finally figure this out!