[Hardware Bug] pi-top Prevents full PowerCycle

@duwudi and @wil, I think this will be most relevant to you guys. Currently, while I’m waiting for the display bridge, I’ve been playing around with swapping ad cards and other operating systems, etc. However, with the display adapter and FHD display, I’ve noticed that I keep wracking my head when swapping cards.

Then I noticed that the red power led doesnt go out when shutting down. Turns out that the raspberry pi inside is receiving power through the mini-HDMI connector from the display adapter. If you dont swap any sd cards, it’s great! But the moment you start changing OS’es by changing cards, it hasnt completed a full power cycle and fails to even start reading the card.

In a nutshell, you can power off, power on, restart and be on your happy way while still being plugged in to everything. But if you swap sd cards, you need to unplug the mini-HDMI connector before the red power light will go out and it completes a power cycle.

1 Like

Thanks for the report @Supernovali

To clarify, what OS are you using when the Raspberry Pi / pi-top isn’t fully shutting down?

If not using pi-topOS, you’ll need to have a few pi-top services installed on whatever alternative OS you’re using. These inform the hub inside the pi-top that the RasPi intends to shutdown, and that the hardware should follow suit and stop supplying 5V.

@pi-topMIKE Do we have the procedure for installing pi-top drivers on alternative OS’s written up somewhere? I know we’ve talked about it a lot but can’t remember if it’s documented yet.


Also from your description there, I’m 90% sure that the strange behaviour you’re seeing with the micro-HDMI isn’t back-power (AFAIK this isn’t possible) - it’s the pi-top hub MCU deliberately keeping the system up. Figuring out exactly when the RasPi has finished shutting down (and so knowing it’s safe to kill its 5V supply) is a more complicated task than it sounds. We use the detection of a valid video signal, among other things, as an indicator that the RasPi is still ‘alive’, cutting power only when the ‘valid signal’ condition is no longer met. I suspect this is what you were seeing, but I’d have to know more about your setup to be sure.

1 Like

Whether it is RaspbianOS or SiriusOS (pi-topOS), it doesn’t make a difference. Even after making sure everything is up to date and all eeprom firmware is up to date as well.

That makes sense… I wonder what is causing a valid signal to persist then, and why it fails to boot from a new SD card after shutting down until the video cable is removed. I’m glad I figured it out though, I was wracking my head for about an hour haha

1 Like

Ah, so it happens when swapping from one SD card with pi-topOS on it, to another SD card with pi-topOS on it? Well now this just got interesting :nerd_face:

Is it possible there’s something interfering with your I2C lines (GPIO2&3?) We’ve seen situations before where blocked I2C lines stop the Pi from telling the hub to shutdown… what’s your full setup, would you mind sharing a picture?

1 Like

No, I’ve nothing connected to the GPIO at the moment. Yeah, when I get home tonight, I’ll send a picture of it. It is really a clean configuration, mostly just USB being used with power coming in from USB C

But yeah, the process is:

  1. shutdown, red light stays on, swap SD card, and try to boot. You get nothing.
  2. shutdown, redlight statys on, swap SD card, remove then insert mini-HDMI, and try to boot. Works 100% of time

Oh oh oh! Do you guys send I²C over mini-HDMI or does the USB interact with the I²C? I know the FHD display uses I²C because I had to run lines on my display bridge. If it interacts with it, then that could hold the lines busy.

I’ll also check with my other monitor and see what the results are when I get home too

That I2C is purely the HDMI one coming from the pi’s HDMI ports, nothing to do with GPIO.

The issue with back-powering over HDMI needs to be resolved on a future iteration of the Display Adapter - we just need to add an ideal diode reverse current block. Something like the following diagram:



Ok, yeah. I’ll have to add it to the design for my final revision too then

You shouldn’t need to do this for the adapter as the display will never be powered from any other port apart from your adapter. The only reason it’s a problem on the Display adapter is because there are multiple ports with two-way power on them

1 Like

Ah, good point. Needless to say, I’m tired. Its midnight-30 over here haha

Ohhhh wait a second, sorry guys, when you’ve been talking about using the “display adapter”, you’re talking about one of these things:


Sorry @Supernovali, I misunderstood your set up … I haven’t seen many of these ‘in the wild’ so I just assumed you meant pi-top display cable, and was a bit confused. My bad, I should have asked for clarification before jumping to conclusions! I can now see how back-powering could happen there… although I have to admit I’m surprised that the RPi hardware even allows this to happen :crazy_face:

1 Like

Hahaha, no worries! I called it that but I don’t know if that’s the official name. I bought the DIY version of the pi-top and didn’t get the display adapter so I’ll have to wait for my display bridge to get here (when ever that is going to be) to get rid of the jubmle of wires hahaha.

I’m surprised it allows it too! I mean it makes sense that power can be sent over the HDMI for small screens that don’t draw more than 500mA or so, but still haha

PS. I got so tired last night, we didn’t leave my moms house until 1030 and by the time I got home, it was too late to test with other monitors. But my guess is that normal monitors don’t supply power over HDMI… do you know if this assumption would be correct? It would save me moving the “jumble” around to find out hahahaha

The display adapter comes with the FHD screen not the pi-top :stuck_out_tongue:

HDMI actually has the capability to carry power, audio (both ways), video and even Ethernet but sadly no one actually uses the Ethernet capabilities, imagine the jumble of mess of wires that would be tidied up if you could network with HDMI?

1 Like

Oh, I have a 25’ HDMI cable but It’s one thic-boy though hahaha :joy::rofl: inuuendoe’s aside, hehe, I think I made a typo and meant display cable, not display adaptor. The display adaptor seems to back-feed power to the pi through the mini-HDMI port, where-as the display cable provides power to the display through the pi-top. It’s just a nuisance as it prevents the pi from completing a power cycle :confused: