kme
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 4:31 am

I\'m having a little trouble to understand the current flows on the USB bus. I realize that a Raspberry-PI itself can\'t feed anything more power demanding than a keyboard, mouse or USB storage stick. No 2½\" HD and such.

But what if I have a powered USB hub like i.e this: www.amazon.co.uk/Edimax-EU-4230-USB-100 ... B0029VJK5E

This one can power down stream devices by its own PSU, but can it also feed the R-PI upstream? R-PI uses less power than a 2½\" disk.

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abishur
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 6:22 am

The only real issue I foresee with powering the r-pi off any USB hub is the initial power on. As I understand it, a USB hub only sends 100 mA until the device negotiates for more power. Will the r-pi be able to do that from an off state? I don\'t think so. If I understand this correctly, it\'s a micro USB port in form factor only (I don\'t believe it actually connects to a USB port). So if we treat it as a regular power jack, then it won\'t get the power it needs until the hub sends enough power, which the hub won\'t do until it\'s asked for more power.... well you see where I\'m going with this. But I\'ve heard of pandaboard or beagleboard people doing this so either there must be a way to get the hub to send out more power on one of the ports all the time and not just on request.
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 12:41 pm

Thank your for your answer abishur.

To me there is two very different scenarios here:
1) The hub power the P-PI via the normal USB port. This might be behaving like you describe.
2) The hub is connected to R-PI with USB-microUDB cable. If I have understood the Universal Phone Charger standard the microUSB connectror isn\'t a data line but only a plain two wire DC connector. If this is so, the R-PI has no way to signal to the hub to wait before giving full power, and it must be full power instantly. Or am I wrong?

The down side of 2) is that you take up two ports on the hub (one for normal USB operation, one for power feed) and that makes a three port hub pointless. And so far I\'ve only found three ports hubs if I also want a LAN port (I do).

My goal have a B model with more ports but minimal external stuff, so I was thinking of the A model and said hub and trying not to have two DC adapters. That\'s simply too clumpsy.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 2:15 pm

The second one is what I\'m describing in my above post. It\'s my understanding that it is a usb port in form on (so saying that you\'re using a port just for power might be a misnomer as it wasn\'t an additional port to begin with and you\'re still starting off the the advertised one or two USB ports)
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 2:19 pm

Dealeted - Combined posts to the single post that follows.

hippy
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 2:19 pm

[quote]Quote from kme on October 30, 2011, 04:31
But what if I have a powered USB hub ... This one can power down stream devices by its own PSU, but can it also feed the R-PI upstream? R-PI uses less power than a 2½\" disk.[/quote]

As abishur says it will depend on the hub. If the hub provides enough power when turned on it will work but a USB specification compliant hub should not provide more than 100mA so will not work.

The following are the two standard ways to use an R-Pi ( and any other device ) -

[img]http://www.raspberrypi.org/wp-content/u ... -NOHUB.gif[/img]
[img]http://www.raspberrypi.org/wp-content/u ... LUSHUB.gif[/img]

A third option is to simply split the power supply for the hub to also provide power to the R-Pi. This will only work if the hub supply is compatible with the R-Pi power input. The simple solution there is to find a hub which uses a 5V supply and has a PSU that is compatible with the R-Pi power intput.

[img]http://www.raspberrypi.org/wp-content/u ... LITHUB.gif[/img]

If the split power supply is undesirable because it uses two cables ( power and USB to hub ), then a slightly more complex splitting arrangement can bring those down a single cable as below -

[img]http://www.raspberrypi.org/wp-content/u ... LITBES.gif[/img]

Advanced hardware hackers can start cutting tracks on the R-Pi and within the hub and do all the splitting internally, giving an elegant, one \'normal USB cable connection\' and nothing else between R-Pi and hub, but that\'s probably not recommended for most cases. The splitters will not be that complicated to construct.

Because the R-Pi cannot be powered through its outgoing (host) USB ports, only the micro-USB power input, and the hub will not provide power back through its input connection, it\'s no simpler to take power from a hub output, it would still require some additional splitting to use a single cable, and you lose access to one of the hub outputs -

[img]http://www.raspberrypi.org/wp-content/u ... HUBPWR.gif[/img]

There\'s no real gain in that so my suggestion is not to worry about powering the R-Pi from a hub but to look at the simpler method of splitting the power supply before the hub. That\'s also going to work for USB specification compliant hubs.

The case where taking power from a hub output would make sense is where the hub is not powered by a 5V supply; where you will be using the hub to create a stable 5V supply for the R-Pi.

I\'ve rated the power supplies for the maximum devices connected ( up to a four port hub ) and assumed 700 mA current draw for the R-Pi ( adjust as appropriate ).

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 2:59 pm

Hippy - several of your suggestions require that the hub PSU supplies a stable, regulated 5.0 V and I think this is a bit dangerous assumption to make. Voltage regulation might easily go on inside the hub.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 3:14 pm

[quote]Quote from kme on October 30, 2011, 14:59
Hippy - several of your suggestions require that the hub PSU supplies a stable, regulated 5.0 V and I think this is a bit dangerous assumption to make. Voltage regulation might easily go on inside the hub.[/quote]

Thanks. I realised that and was editing while you posted that, and you are absolutely correct. It does rely upon a PSU that is regulated enough to provide correct R-Pi power.

The splitting arrangement for a hub that took in other than 5V power would be as below -

[img]http://www.raspberrypi.org/wp-content/u ... BSPLIT.gif[/img]

Whether that works or not rests, as mentioned, on whether the hub puts out 5V > 500mA when turned on and in use. USB specification compliant hubs should not permit that.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 4:01 pm

Thanks for the illustration hippy. No. 3 is what I\'ve been using for a year now on my Beagleboard. Didn\'t use the rather flimsy wall wart style PSU that came with the hub and bought a proper \"power brick\" regulated one. Spliced, switched and fused and now feeds board and hub independently. Makes for a clean installation and provides a dependable power supply solution. Easy when you\'re able to power both from a 5V source so I welcome this move for the Raspberry Pi of course.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 4:18 pm

Thanks for the very complete and legible post, Hippy.
I\'m shooting for yet something else for my hack RPi: powering it off my PC\'s USB port, and not connecting it to anything else since I\'ll be sshing into it to mess around.
My server RPi won\'t need a hub, and I think its 3.5\" HD takes 12V not 5V, so it will have its own, dedicated PSU, probably the leftover one from my Touchstoned HP Touchpad, if it deigns to work on non HP stuff (my Nook Color\'s USB cable doesn\'t want to charge anything but the Nook....).
I\'m sure the nice folks at the Foundation will accept slightly-smoke-smelling RPi returns under warranty ^^

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 4:39 pm

Well, does this mean that my phone actually asks for more power even when turned off?And there are some cables (according to some site, perhaps even wikipedia) in which the data lines are shorted, and I\'m expecting that the power cannot be negotiated when you have no data line? So I hope there are ways to power the Raspi out from a standard hub.
On a side note, I would expect some setup similar to the proposed ones being done with the A model too, that means you have to spare as many USB ports as you can (since you only get 3 if you power the raspi from the hub), so I hope there are some other ways to inject power directly into your raspi.
BTW: the USB+ethernet hub posted by OP made me wonder: if a standard USB hub has 4 outputs (4xUSB or 3xUSB+LAN), what happened to the last USB on the internal raspi hub? (lan + 2xUSB + one gone missing?)
I ask because a 3xUSB out could really remove the need for an external USB hub for adecent chunk of users (especially people originally intended as an audience) (and I do understand this is not happening anytime soon).

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 4:48 pm

@ Tide: You may be right this is the most feasible solution. Not exactly what I was looking for though.

Can you recommend a commonly available high power (15+ W) regulated PSU? I\'m after an off-the-shelf solution but during my googling I came across this diagram for a 25 W unit:
http://www.simple-electronics.com/2011/ ... upply.html
Although I don\'t know much about electronics, even I can see the components are very cheap.

Maybe such a PSU is an item for the Raspberry shop? Most people would be happy with the default UCS but some can\'t resist to make problems for themselves :-)

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 5:00 pm

Strangely, the USB+Ethernet chip used for the Model B does only have 2xUSB and 1x ethernet. No hidden nor wasted 3rd USB port here. That\'s a bit weird, especially because the pure USB circuit from the same supplier does have 4xUSB.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 5:09 pm

The question is if the hub senses the power draw or looks for activity on the data lines. If it senses the power draw and ramps the power level up to the demand topping at 500ma then it will be no problem to run a line right from the hub to the power port of the RasPi. I suspect that the cheaper hubs do work this way, if they just do not supply power all the time. The power saver hubs will probably be the most problem. They might look for activity on the data lines.

Number two will probably be the easiest for the majority of people. Number three will probably be used a lot by us hobbyist. Number five is going to be more popular than you think it will @hippy, the number of ports needed for most RasPii is going to be rather low. Example for a model B, 1 RasPi port to the hub, the other RasPi port to a keyboard, you still have three more ports on the powered hub now. This assumes they only buy a 4 port hub instead of a seven port.

@kme so now you are on the other side of the argument, a true debater you are then! lol!

@hippy good post! You only forgot one method, the one I will use.
A 12v into the router, then a inline 5v regulator to the RasPi. Probably a second regulated 5v to a stripped down powered hub. I had hoped to fit it all inside, the routers case, but it probably will not all fit now that the RasPi is only 5v. I will have to move it all to a project case now. And I wanted that innocent \"I\'m just a router\" look. Oh well!
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 5:30 pm

[quote]Quote from obarthelemy on October 30, 2011, 17:00
Strangely, the USB+Ethernet chip used for the Model B does only have 2xUSB and 1x ethernet. No hidden nor wasted 3rd USB port here. That\'s a bit weird, especially because the pure USB circuit from the same supplier does have 4xUSB.[/quote]

The LAN9512 and the LAN9514 both have the same number of pins. It is my guess that the pins that empty have the connections broke inside the IC. There are six unused pins in the 9514. Two for power a four for data. And of course the RasPi has no lines to USB ports for a 9514. This was discussed in another post.
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 5:41 pm

[quote]@kme so now you are on the other side of the argument, a true debater you are then! lol![/quote]Well, I would be an idiot if I didn\'t listen to sensible arguments and as my original idea isn\'t feasible I just have to evaluate options. I just want more USB ports and minimum clutter. I couldn\'t care less if the hub feeds the R-PI or the R-PI feeds the hub, but I can not accept to have two PSUs and just the external hub with cable is bad enough already. And I do need LAN and more than two USB for my intended purpose.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 5:52 pm

[quote]Quote from kattle87 on October 30, 2011, 16:39
Well, does this mean that my phone actually asks for more power even when turned off?
[/quote]

Quite possibly, but it helps to remember that most people charge their phones with special chargers that came with said phone providing for a quick charge, these devices tend to work like other standard battery chargers and ignore the fact that it\'s a USB port (that is to say they charge for a short time at high mA, then a lower steady current, and finally a very low floating top off charge to keep things fresh). When it\'s connected to a computer, however, I\'ve noticed that my phones have tended to take an extremely long amount of time to charge even when powered off. If this is because it doesn\'t auto-negotiate, or because the 100 mA gives it enough power to turn on just enough to negotiate for more power, but 500 mA is still lower than the output of the charger that came with my phone... well I\'m sure that varies by manufacturer.

[quote]
And there are some cables (according to some site, perhaps even wikipedia) in which the data lines are shorted, and I\'m expecting that the power cannot be negotiated when you have no data line? So I hope there are ways to power the Raspi out from a standard hub.
[/quote]

That again would be cables that came with the special charger shipped explicitly for phones. It essentially ignores the fact that it\'s usb and just uses a regular charger hooked up to a usb form factor. As such one might describe the charger as forcing the current down rather than the device requesting the increased draw.

[quote]
BTW: the USB+ethernet hub posted by OP made me wonder: if a standard USB hub has 4 outputs (4xUSB or 3xUSB+LAN), what happened to the last USB on the internal raspi hub? (lan + 2xUSB + one gone missing?)
I ask because a 3xUSB out could really remove the need for an external USB hub for adecent chunk of users (especially people originally intended as an audience) (and I do understand this is not happening anytime soon).[/quote]

[Off Topic]
As Obart said, there\'s no hidden USB port I fear. The chip being use (LAN9152) is a combo usb hub and usb->ethernet adapter and while it might seem odd there\'s actually several reasons it\'s being used

1. By having the ethernet and usb on the same chip it both saves money and keeps the total size of the pcb down (which saves more money) and removes the need for additional data lines and possibly even another layer (which saves even more money!)

2. By using the 2 port model rather than the 4 port model they (are you ready for this?) save money :P :D Not only is the chip cheaper and not only do they save money on not have to place the additional two ports on the board (thereby keeping the footprint down, etc, etc), but one thing we often forget is that the PCB is incredibly small, to add the 4 extra data lines and 4 extra power lines is an incredibly difficult task. Indeed, they already had to drive the layers from 4 to 6 layers. 8 lines would probably create the need for a seventh layer.

While these costs are undoubtedly under 10 dollars per board in the long run, on a project that is coming down to the penny to meet a low price point, each additional dollar adds up in a big way! Plus I\'d wager that most the applications a hobbyist would use a board in would require 2 or less usb ports (media center for TV, web server, proxy filter, arduino substitute, security system (just thought of that one ;) ), the list goes on). Even for a desktop replacement, the only pinch point would be the printer, and if each board cost me an extra 5 bucks a pop, I\'d be better off buying a cheap print server and making my printer a network printer than having to pay an additional price on each board I planned on buying.

Well that was rather off topic, but I hope it answered your questions ;)
[/Off Topic]
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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 6:15 pm

by \"buying a cheap print server\", you mean, \"buying a Pi and setting it up as a print server\", riiiiight ?

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 6:48 pm

[quote]Quote from Lob0426 on October 30, 2011, 17:09
@hippy good post! You only forgot one method, the one I will use.
A 12v into the router, then a inline 5v regulator to the RasPi.[/quote]

Good point, and for completeness -

[img]http://www.raspberrypi.org/wp-content/u ... HUBREG.gif[/img]

That 5V regulator could either be a 7805-style ( would need some heatsinking ) or a switching regulator.

There are also power bricks for many products which can deliver 12V and 5V and thus deliver the two supplies to hub and R-Pi - I was recently looking at XBOX 360 PSU\'s and those give something like 12V at 10A and 5V at 1A which could work in this setup. A genuine PC PSU would work, and even power bricks for external CD-Rom etc. There\'s nothing to stop someone building a complete PSU for themselves if they want. It\'s really just a question of how to best wire things up, how to split power to the right places.

A supply with beefy 12V would also be handy if one wanted to put the R-Pi in a case with a LAN router/switch as well.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 6:49 pm

Usb as a power source in r-pi is great idea and I think single psu for hub and r-pi would be really practical! I use similar sized freescale imx53qsb board (I know this HW is different) and I can confirm that external psu power is needed only when you turn on board. Once it is on and connected to usb hub you can disconnect boards psu and it won\'t power off. I don\'t know if this is side affect of badly designed hub or bug in board layout.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 6:58 pm

[quote]Even for a desktop replacement, the only pinch point would be the printer, and if each board cost me an extra 5 bucks a pop, I\'d be better off buying a cheap print server and making my printer a network printer than having to pay an additional price on each board I planned on buying.[/quote]You must be living in a different world than me. One keyboard and one mouse and you are currently out of ports. No space for a USB storage unit (and you want one - running off the SD will be painfully slow) and no spare port for i.e. the printer. Buy a printer server? Sure nice. Around here that is ~35-40 USD without local VAT and without shipping (which will be ~9 USD). And no, it isn\'t something fancy, just quite minimal (http://www.hardware-store.dk/printerser ... _2861.html). An external hub will be about the same.

So would I happily pay 10-20 bucks extra for a four port Model B? Hell yes, that would be a bargain. And no hardware clutter.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 7:57 pm

[quote]Quote from obarthelemy on October 30, 2011, 16:18
I\'m shooting for yet something else for my hack RPi: powering it off my PC\'s USB port, and not connecting it to anything else since I\'ll be sshing into it to mess around.
[/quote]

That should work. Again, as long as the PC\'s USB supplies enough current, and if not it should be easy to swap the the USB socket to use the PC\'s PSU 5V if it\'s on a cable to motherboard connection. Add a fuse or use a 5V regulator from 12V if wanting to protect the PC from fault conditions on the R-Pi.

Though an R-Pi USB port could be jumpered over to the mini-USB it seems both PC and R-Pi will be USB hosts so not possible to simply add some USB network drivers to both and have a single USB cable network connection between the two.

Given that, it may be better to do the same sort of thing as described, but use a splitter ( or jumper the RJ45 to micro-USB socket ) and inject power up the LAN cable PoE-style. It won\'t be IEEE 802.3af compatible but many people have used the technique to carry 12V or 5V to where needed.

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Re: Can a powered hub feed R-PI?

Sun Oct 30, 2011 11:36 pm

No need for a 4 port USB, but a 3 would be nice... you could probably even fit that more or less \"comfortably\" by placing the third port vertically and not horizontal. But well, my use for the raspi gonna be headless server or mobile computing, that means I will be either getting model B with no hub or model A with a hub. It\'s just that the model B is a bit less... \"flexible\" then one might expect.
I repeat, it fits perfectly my needs, therefore I\'m really happy because I\'m saving money, but I guess it won\'t be the same for some people (children?).
And anyway, since they went 6 layers, they probably have enough spare space around for the extra 6 lines for the third USB! (I\'m joking don\'t worry).
I guess a keyboard with additional trackball is gonna be the favored input device by most people... I really suggest selling one as an optional! (it really makes sense: a keyb&track is even easier to move around then a keyboard with mouse).

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Re: Can a powered hub feed R-PI?

Mon Oct 31, 2011 12:17 am

[quote]Quote from kme on October 30, 2011, 18:58
[quote]Even for a desktop replacement, the only pinch point would be the printer, and if each board cost me an extra 5 bucks a pop, I\'d be better off buying a cheap print server and making my printer a network printer than having to pay an additional price on each board I planned on buying.[/quote]

You must be living in a different world than me. One keyboard and one mouse and you are currently out of ports. No space for a USB storage unit (and you want one - running off the SD will be painfully slow) and no spare port for i.e. the printer. Buy a printer server? Sure nice. Around here that is ~35-40 USD without local VAT and without shipping (which will be ~9 USD). And no, it isn\'t something fancy, just quite minimal (http://www.hardware-store.dk/printerser ... _2861.html). An external hub will be about the same.

So would I happily pay 10-20 bucks extra for a four port Model B? Hell yes, that would be a bargain. And no hardware clutter.[/quote]

Really, dang you live in an area with expensive print servers. I\'d definitely go with obart\'s idea and just use an r-pi.

And yes, as I said I have one r-pi which I would need more ports on. One of the 5 I\'m planning on getting initially (albeit spread out as the pocket book allows ;) ) But, as I said, I\'m not buying each one to be a desktop replacement nor would I expect the majority of model B\'s being sold to need the second port. The media server only needs a wireless keyboard/mouse combo attached to it and an HDMI cable (and even if I had to separate them out that would still fit on two usb ports). The web server is headless and only has an ethernet cable. My NAS will also be headless with a single external hard drive connected to it... I guess now that I\'m thinking about it I\'m not using the r-pi for any purpose in which I would need more than two USB ports.

Which really is my point here. For most the applications an r-pi would be used for by hobbyists, two ports will be sufficient, for the small number who would need more they\'d come out ahead buying a single external hub. It also makes sense from a finical point of view for the community at large, why burden everyone with ports they don\'t use so that the few who would need it on one or two of the pis don\'t have to pay for an external hub? Humorously, I just looked at the back of my desktop PC. It uses one USB port, the keyboard is PS/2 (They\'ll have to pry that keyboard from my cold dead hands!) Not even my main rig needs more than two slots. (Though I will freely admit it helps that it has all the internal storage it needs)
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Re: Can a powered hub feed R-PI?

Mon Oct 31, 2011 1:14 am

[quote]Really, dang you live in an area with expensive print servers. I\'d definitely go with obart\'s idea and just use an r-pi.[/quote]Right - $25 for an A model and a UCS adapter to at least the same price and as we all know $50 is less than $35-40... Lehman Brothers didn\'t exists in vain.

The fact is that the LAN9514 and an extra two-port USB stack is max $5 extra in components and no matter how I twist things I\'m going to pay at least $30 extra if I want extra USB ports. The party killer for a fictional 9514 solution is if it\'s completely impossible to accommodate the extra four data lines for the extra two-port stack. The power lines are there already and both the LAN9512 and 9514 are non-powered so extra power lines isn\'t likely to be needed (maybe a bit wider though).

Never mind, this isn\'t going to happen so I just have to figure out how to make the least cluttered setup and then pay what it takes. I was just hoping I could somehow feed USB power-only, but it seems not likely.

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