doveman
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Excessive current usage

Thu Jul 25, 2013 8:22 pm

I've got three Belkin F5u700 USB2 hubs. I've disconnected the LEDs from one of them to see if they were generating the heat but it's not that.

All three get awfully hot when connected to the RPi. I'm using the LED-less one at the moment and whilst it's not quite burning temperature but it's still quite uncomfortable to put my finger on the usb ports and there's also a lot of heat coming from the top and bottom of it.

I've plugged one of the spares, with the LEDs intact, to a hub connected to my PC and that hasn't got warm at all. The 7-port desktop PC hub it's plugged into, with about 5 devices connected, is a bit warm on the top and bottom but not at all around the ports. I also connected it directly to the PC in case that might make a difference. Windows detected it and installed drivers but it's still not heating up.

I only had a Remote receiver plugged in the hub connected to the RPi, so I disconnected that but it still stayed just as hot. Then I disconnected the external power (coming from a ubec), so just the RPi lead is connected and it's still just as hot. If I disconnect the RPi lead and just connect the ubec power, it doesn't get warm, so it seems the RPi must be doing something strange to it!
Last edited by doveman on Thu Aug 01, 2013 4:26 pm, edited 1 time in total.

jdb
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Re: Hub getting hot

Thu Jul 25, 2013 8:38 pm

Weird.

What is your TP1-TP2 voltage on the Pi with the Pi's power supply on?

The only thing I can think of is internal and external power supplies fighting each other. Can you do a "loopback" power test? i.e. use hub external power, then plug one of the downstream hub ports with a USB A - micro B cable, then power the Pi from that?
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doveman
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Re: Hub getting hot

Thu Jul 25, 2013 10:01 pm

I get about 5.11-5.15v across TP1-TP2.

It can't be the power supplies fighting each other as it gets hot with just the RPi USB cable connected to the hub, so the hub is only getting power from the RPi.

I'll try powering the hub and then the RPi from the hub as you suggest though, rather than through the GPIO, to see if it makes any difference.

doveman
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Re: Hub getting hot

Fri Jul 26, 2013 2:13 pm

Well powering the RPi from the hub's no good as I only get around 4.6v across TP1-TP2 and weird things were happening after it booted.

The whole point of getting a ubec was to provide stable power to the RPi, so I really need to power it that way.

I can only think there must be something wrong with the RPI's USB A ports (or more likely the firmware controlling them) so that it's causing activity on the hub's chips when it shouldn't be. I'm not sure I can but I guess if I could measure the current draw in the hub when connected to the RPi as compared to when it's connected to my PC that would confirm this.

doveman
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Re: Hub getting hot

Fri Jul 26, 2013 5:48 pm

I tried running it with just the cable from the RPi to the hub and without the SD card in and it doesn't get warm at all like that. With just the SD card in and not the USB stick, which /storage is on, so that OpenElec can't finish loading and halts at the OE splashscreen, the hub does get hot, so it's either the firmware or something in the initial stages of OE that's causing this.

doveman
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Re: Hub getting hot

Mon Jul 29, 2013 5:25 pm

I've tested with a completely different make of hub that I've borrowed from someone now and that gets hot as well. It's the two controller chips on the underside of the board (it's a 7-port hub, so basically two hubs cascaded internally) that are getting hot. Plugged into my PC, these chips stay completely cool.

I've also tested with a Raspbian Wheezy image I downloaded from http://www.raspberrypi.org/downloads just to check it wasn't something peculiar to OpenElec but that's just the same, so it seems it must either be the firmware or a fundamental fault in the boards (seeing as I've tested two and they both cause this).

So do I have to return them for a refund or was there just a bad batch that were affected by this fault and so any replacement I accept will not have this problem?

jdb
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Re: Hub getting hot

Mon Jul 29, 2013 11:03 pm

Can you substitute the A-B connector from the Pi to the hubs for another? One possibility is a cable with a short in it. If not, then if you substitute the Pi for another, do the hubs still stay hot?

If your problem goes away when substituting the Pi for another then the Pi is defective and should be RMA'd.
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doveman
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Re: Hub getting hot

Mon Jul 29, 2013 11:41 pm

Yep, I've tried several cables, several hubs and two RPi and have the same problem with all of them. I think I've ruled out the cables or hubs being a problem as using them on my PC the hubs don't have this problem.

doveman
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Re: Hub getting hot

Wed Jul 31, 2013 1:18 pm

I've done some further tests with two RPi and a PC for comparison:

Code: Select all

RPI powered from 1A phone charger:

 USB Hub not connected at all:
     RPI Voltage (TP1-TP2): 4.62v
     USB output voltage: 4.58v
     USB TX line (pin x): 0.0v (with respect to ground)
     USB RX line (pin y): 0.110 - 0.150v (with respect to ground) 

 USB Hub not-powered and connected to RPI (USB power lines only):
     RPI Voltage: 4.6v
     USB output voltage: 4.58 VDC
     Current Drawn: LED Hub 9.23ma, other model (non-lit) hub 6.87ma

 USB Hub not-powered and connected to RPI (all four USB lines connected):
     RPI Voltage: 4.55VDC
     USB output voltage: 4.53VDC
     Current Drawn: LED Hub 139.5ma
     borrowed hub (non-lit) hub 109.6ma

 2nd RPi:
Belkin LED USB Hub not-powered and connected to RPI (all four USB lines connected):
     RPI Voltage: 4.64v
     USB output voltage: 4.69v
     Current Drawn: 145.0ma
     USB TX line (green): 0.100v (with respect to ground)
     USB RX line (white): 0.097v (with respect to ground)

 2nd RPi:
 borrowed (unlit) USB Hub not-powered and connected to RPI (all four USB lines connected):
     RPI Voltage: 4.75v (4.77v without network cable connected, was plugged into 1st RPi for all tests)
     USB output voltage: 4.75v (4.77v without network cable connected)
     Current Drawn: 110.0ma
     USB TX line (green): 0.104v (with respect to ground)
     USB RX line (white): 0.102v (with respect to ground)
As you can see, the 2nd RPi has somewhat higher voltage both on the board and coming out the USB socket. The hub chips are heating up just the same with both RPis though.

I did a couple of tests with the PC which I think show the problem. The current draw with the Belkin LED hub is initially 125ma but then quickly drops to 78ma and then settles at 12ma, so I presume the initial higher draw is just whilst Windows detects and installs the device, whereas the RPi appears to be keeping it at full draw when idle. If I plug the remote receiver into the hub however, it goes back up to 125-130ma. I'm not sure what to make of this, as the hub still doesn't get hot when connected to the PC with the remote receiver plugged in.

The borrowed hub goes 80ma, 50ma, 8ma. With this hub however, when I plug the remote receiver in, it only goes up to 22ma.

So the problem appears to be that the RPi is making the hubs run at full power all the time for some reason.

doveman
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Re: Excessive current draw

Thu Aug 01, 2013 4:25 pm

I did some more testing. I've discovered that the borrowed hub is USB 1.1, not 2.0 like the Belkin, so it's probably not surprising that it uses a bit less power. Also probably obvious but I've realised that plugging devices in the 2nd half of a cascaded hub result in more power draw, because it has to power both chips. This isn't really an issue with the RPi though as it doesn't support cascaded hubs, so the second half/set of ports can't be used anyway. It also appears that my meter in the circuit is preventing devices plugged into the hub from working properly on the RPi so it's hard to get an exact figure for the draw from active devices.

Still there's clearly a problem in that the RPi keeps whichever hub I use at full load (110-150ma), whereas on the PC they will idle at 7-12ma, which I think is a shocking waste of power on what's meant to be a low-power, green and cheap to run device (not to mention the extra wear it must cause on the hub and maybe the RPi as well). In the UBS1 hub the remote receiver uses 142ma on the RPi compared to 79ma on the PC and in the USB2 hub it uses 162ma compared to 109ma in the PC.

Code: Select all

borrowed (unlit) USB 1.1 Hub not-powered and connected to RPI (all four USB lines connected):

Raspbian Wheezy:
Empty/Idle - 109ma
Keyboard - 110ma
Remote receiver - 142ma

on PC: 
Empty/Idle - 7.9ma
Keyboard - 12.3ma (but not working)
Remote Receiver - 72ma on 1st hub chip, 98ma on 2nd hub chip (was properly installed but couldn't test if working)


LED USB 2.0 Hub not-powered and connected to RPI (all four USB lines connected):

Raspbian Wheezy:
Empty/Idle - 151.4ma (whilst booting and at desktop), 
Keyboard - 153.6ma
Remote receiver - 162ma

With PC:
Empty/Idle - 12ma (120ma whilst installing), 
Keyboard - 87ma on first hub chip, 129ma on 2nd hub chip
remote receiver - 109ma on 1st hub chip, 143ma on 2nd hub chip

Frodo 12.1:
Empty/Idle: 
10ma at power on, 87-127ma during OE splashscreen, 98ma after splashscreen disappears and at XBMC Home

With remote receiver connected (to first hub chip):
24ma at power on, 167ma during boot and at XBMC Home

broo0ose
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Re: Excessive current usage

Thu Aug 01, 2013 8:53 pm

Interesting, I had one Pi that was always loosing its WiFi signal. When I took the USB adaptor out it was really hot so I wondered if it was overheating. I have now put it on the end of a USB extension cable and it seems to be keeping its signal (touch wood).

Obviously I have not reduced the current, I've probably increased it slightly. But maybe the combined heat from the USB port and the adaptor was enough to overheat it.

doveman
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Re: Excessive current usage

Fri Aug 02, 2013 12:41 am

I too found I couldn't put my USB remote receiver directly in the RPi without the receiver locking up within minutes but it worked OK in the hub.

I tested it earlier using an extension cable and that worked so maybe that also helped by reducing the heat, although I was using Frodo 12.1 at the time so maybe there's just a bug with Gotham, which is what I was using when I first encountered the problem.

I measured the current used by the remote receiver on the extension cable in the RPi and it was around 37ma, rising to 47ma when receiving a signal. Even in the USB2 hub connected to the PC it uses 109ma, which seems a lot of overhead for the hub but it's still quite a bit lower than the 162ma when it's connected to the RPi.

doveman
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Re: Excessive current usage

Sun Aug 04, 2013 1:35 am

Did a quick test with a recent Gotham build.

With the hub powered straight from the 5v ubec and not through the RPi, there's only 0.17ma on the USB cable with the remote receiver plugged into the hub. Once I disconnect the power cable from the hub, this shoots up to 194ma, which is higher than Frodo 12.1 at 167ma.

Either way the hub gets just as hot even when empty, so the problem is clearly that the RPi is causing the hub to run at 100% unnecessarily.

Interestingly, I just read this which says that self-powered hubs are limited to a max of 100ma which is exceeded by either of the hubs I've tested on the RPi (and with the Belkin, on the PC for that matter).

http://www.edn.com/design/wireless-netw ... management

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FTrevorGowen
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Re: Excessive current usage

Sun Aug 04, 2013 2:03 pm

doveman wrote: ...
Interestingly, I just read this which says that self-powered hubs are limited to a max of 100ma which is exceeded by either of the hubs I've tested on the RPi (and with the Belkin, on the PC for that matter).
...
My understanding (which may be incorrect) was "100mA per port" ie. for a 4-port hub 400mA for the 4 ports + 100mA for the hub (electronics) = 500mA = the maximum for a "powered hub port". However, virtually all of the, albeit "low-cost", hubs I've investigated, powered or unpowered, seem to have all of the ports power connections "in parallel" (see http://www.cpmspectrepi.webspace.virgin ... allXP.html ) and I've certainly been able to passively draw >500mA from some (see http://www.cpmspectrepi.webspace.virgin ... st_Results ).
Trev.
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, B2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, A+ and a B2) but Buster on the P4B's. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

doveman
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Re: Excessive current usage

Sat Aug 17, 2013 1:55 pm

FTrevorGowen wrote: My understanding (which may be incorrect) was "100mA per port" ie. for a 4-port hub 400mA for the 4 ports + 100mA for the hub (electronics) = 500mA = the maximum for a "powered hub port". However, virtually all of the, albeit "low-cost", hubs I've investigated, powered or unpowered, seem to have all of the ports power connections "in parallel" (see http://www.cpmspectrepi.webspace.virgin ... allXP.html ) and I've certainly been able to passively draw >500mA from some (see http://www.cpmspectrepi.webspace.virgin ... st_Results ).
Trev.
Yeah, 100ma per hub wouldn't make much sense would it, when each PC port can supply 500ma.

Anyway, I'm disappointed no-one's acknowledged the problem, let alone suggested it might be fixed. My hub is close to hot enough to burn my finger on the ports, which is just wrong. I connected my large desktop 7-port hub and that didn't get warm but then again I couldn't boot from the USB stick plugged into it either, so it probably isn't compatible and was just totally inactive.

I don't think I could have misread the meter but I'm not sure that 150ma could be causing so much heat, so I'm not sure what to make of it. Maybe there's only some hubs that the RPi can use them without overheating them but I don't have a supply of different hubs to check if that's the case.

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Re: Excessive current usage

Sat Aug 17, 2013 8:07 pm

I have found out the probable reason why your hub draws full active current on the Pi and not when plugged into the PC.

It's because the kernel is currently configured without autosuspend support for USB. The PC, on detecting no devices plugged into the hub, will issue a suspend command that will put the hub into a low power state. Without this suspend, devices will draw normal operational current continuously.

If you leave the upstream port of a self-powered hub disconnected, it will suspend itself.

Lack of autosuspend isn't why your hubs are getting too hot - your hubs have a poor thermal design if the sockets get so hot you can barely touch them. 160mA at 5V is 0.8 watts, which for a box the size of a pack of playing cards is... not a lot.

It would be useful to support though - it would probably stop other devices using lots of current as well. I would need to test various scenarios to ensure that the dwc driver does actually support suspending the root port properly.

[quote="doveman"]This isn't really an issue with the RPi though as it doesn't support cascaded hubs, so the second half/set of ports can't be used anyway.[/quote]

It does, because when you plug a hub into the model B's ports you are cascading the ethernet chip's internal USB hub with the downstream hub.

There is however a limitation on the number of cascaded hubs you can successfully operate with.

USB2.0 spec is for devices plugged into a cascade of 5 compliant hubs to work correctly, the Pi's host USB port currently will operate with USB2.0 devices attached to a cascade of max 3 compliant hubs. USB1.1 devices should operate correctly on the end of a cascade of 4 compliant hubs. These numbers are not inclusive of the model B's own USB2.0 hub.

"Bad" hubs or devices will affect the number of cascaded hubs you can operate successfully - you may have to go down to plugging problematic devices into the Pi's ports directly. USB3.0 devices appear to be a lot worse at operating in a cascade than USB2.0 devices.
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doveman
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Re: Excessive current usage

Sat Aug 17, 2013 11:00 pm

Thanks jbd, I appreciate you looking into this and replying :)

If the kernel could have autosuspend enabled it might help, certainly for those who don't normally have anything plugged into their hubs and just use them to plug in usb sticks occasionally.

However, I have my remote receiver plugged into the hub, so it's never going to be completely idle, yet on my PC the hub barely gets warm like this but gets hot with the RPi, so if it's not lack of autosuspend there must be something else missing on the RPi that the PC does that stops it getting hot. Maybe autosuspend will suspend the second chip and this is what the PC is doing and the RPi isn't that is causing the difference in temperatures, or maybe the PC is able to suspend all the ports except for those in use?

Regarding cascaded hubs, all I can tell you is that I tested my usb sticks on my Belkin hub and on the second set of ports they only manage 700-800KB/s, whilst on the first set they manage a more normal 10MB/s. I can't recall if I tested both USB2 and USB3 sticks but nonetheless, that's only one cascaded hub/chip away from the Pi.

As for plugging troublesome devices into the Pi directly, my remote receiver works fine in the hub but locks up whenever I've tried it in the RPi, so I don't know what to make of that. I imagine it's only a USB1.1 device but I'm not sure.

doveman
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Re: Excessive current usage

Wed Sep 11, 2013 3:08 pm

I'm currently using my second RPi and have it powered the same way, via an UBEC connected to the GPIO but I'm powering the Belkin hub with it's own PSU for now, rather than taking power from the UBEC. Not only is the hub still getting rather hot but so is it's PSU, which is rather alarming, so I hope something can be done to reduce the current draw of hubs connected to the RPi soon.

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