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chill is offline chill
2014-08-07 , 03:51
Posts: 252 | Thanked: 221 times | Joined on Jul 2010
#41
Originally Posted by Estel View Post
Sure, I'll gladly answer The things are easy once you know them, but can be confusing at the start. I remember how many times I had problems with it in the past...

That's why I have put quotas there - I meant general instructions from USB Mode or H-E-N (I assume, that you're using USB Mode).
Hmmm I don't see any USB Mode (I am using it, yes) instruction telling me when to turn on a particular mode if an external +5V source is attached.

Originally Posted by Estel View Post

But, it's all not entirely related to hostmoding on N900. I meant that - in funny twist - those non-compliant hubs are better for N900, as they try to give peripherals connected to them as much current as needed, and can draw those power from N900's side (which can be already "augmented" with power from 3th branch of Y-cable) - which mean that those passive hubs act entirely like active hubs, for all intents and purposes.
Ok, but if you are not hostmoding on the N900, why else would you attach/power peripherals to the N900? In other words, why would you use the N900 purely as a +5V source? Also note that the N900 isn't much of a source anyway, it gives only 200mA.

Originally Posted by Estel View Post
Yes, see above. By the way, if you tinker with it a little, active hub can be powered from the same +5V power source as your N900 is charged from (via 3th branch of Y-cable) - this way, you can carry just one charger with you, instead of two. But for this, you need powerful enough +5V power source. I use a 2A +5V charger, that I have modified to contain two USB ports. I connect 3th branch of Y-cable to it (for charging N900), and another cable for powering active hub, to the 2nd port.
l33t splicing skillz.

One question remains: when you power the peripherals with the N900 (host mode+boost) and an external +5V source, do peripherals draw current from the N900? I am asking because I don't want the N900 battery drained when I have a powered hub at hand, and I can't seem to tell USB mode to go into "host mode+charging" then. Note the powered hub does not (as you mentioned earlier) charge the N900; I guess this is why USB mode won't let me select the charging mode. In fact, as I was switching back and forth between the modes in USB mode, the N900 rebooted.
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Estel is offline Estel
2014-08-07 , 14:23
Posts: 5,028 | Thanked: 8,613 times | Joined on Mar 2011
#42
Originally Posted by chill View Post
l33t splicing skillz.
Veri phunny

Originally Posted by chill View Post
One question remains: when you power the peripherals with the N900 (host mode+boost) and an external +5V source, do peripherals draw current from the N900? I am asking because I don't want the N900 battery drained when I have a powered hub at hand, and I can't seem to tell USB mode to go into "host mode+charging" then. Note the powered hub does not (as you mentioned earlier) charge the N900; I guess this is why USB mode won't let me select the charging mode. In fact, as I was switching back and forth between the modes in USB mode, the N900 rebooted.
The thing will draw only marginal current from N900, but N900 itself uses quite a current (additional ~150 to 200 mA) for the sole fact that it's hostmoding. No idea why. So, it's better to always hostmode+charge, when you have possibility to do so.

As for the thing about passive hubs acting as active ones if they're not standard compliant - scratch it, I can't seem to explain it in understandable way, it seems, and it is not very important thing anyway. Just to clear it up, it doesn't have anything to do with powering things from N900's 200 mA (out of hostmoding).

/Estel
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chill is offline chill
2014-08-18 , 23:14
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#43
Just for the record, I've done it and it works.

The N900 runs warmer: normally it's 33 C when idle, but with host mode it's at 38 C. This goes up to 43-44 C while it's being used intensively.

One thing still doesn't compute, though: if the N900 can provide at most 200mA, and the hub takes one unit of 100mA for itself, there is only 100mA left for the devices. A USBEthernet adapter uses >100mA, so how is it possible that it works? Note the hub is passive, i.e. this is before connecting the external +5V. The only possible explanation is that the hub does not reserve 100mA for itself. My understanding of "non-compliant" was that it gives as much power to the peripheral as needed; I guess mine is "doubly non-compliant" in that it doesn't reserve 100mA for itself.
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Estel is offline Estel
2014-08-19 , 22:26
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#44
Originally Posted by chill View Post
I guess mine is "doubly non-compliant" in that it doesn't reserve 100mA for itself.
That's possible, and encountered quite often. In case of intensive current draw, your hub would just "faint" due to low power, silently. The plus side, is that you can enumerate, and as responsible user, you add external power to y-cable power branch, before starting to use network heavily. In many times, lack of idiot-proof safeguards in hardware can be very helpful

I'm really glad, that you've got it working. BTW, if someone thinks that we're "screwed" due to our 200mA limitation and hostmode implementation - some android tablets were so painfully screwed hardware-wise, that they can't provide *any* power at all, while still capable of hostmoding when correctly hacked kernel gets loaded - it means that they need voodoo'ing with attaching external power to enumerate *anything*, including things like ensuring that power comes to the device to power it up and start enumerating process, but not to the whole line and host, as it would prevent enumerating... (setup based on diodes).

/Estel
__________________
N900's aluminum backcover / body replacement
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N900's HDMI-Out
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Camera cover MOD
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Measure battery's real capacity on-device
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TrueCrypt 7.1 | ereswap | bnf
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Hardware's mods research is costly. To support my work, please consider donating. Thank You!
Last edited by Estel; 2014-08-19 at 22:30.
 

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pichlo is offline pichlo
2014-08-22 , 07:22
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#45
Originally Posted by chill View Post
One thing still doesn't compute, though: if the N900 can provide at most 200mA, and the hub takes one unit of 100mA for itself, there is only 100mA left for the devices.
Not necessarily. To be more precise, USB 2 specifies power in up to 5 steps in 100mA increments. Every device must start as a low power device, consuming one power unit. That is up to 100mA, not necessarily 100mA. Only after a successful enumeration and negotiation with the host for more power is the device allowed to switch to consuming more power unit, up to a maximum of 500mA. At least such is the theory. In practice, this is simplified to "low power" (up to 100mA) and "high power" (up to 500mA).

I have seen compliant devices that take exactly 0mA in the "low power" mode. For example the N900 itself, when connected to the PC. I have also seen non-compliant devices that take more than 500mA before they even connect properly. For example el-cheapo USB HDD enclosures.

Your hub is unlikely to consume the full 100mA. It is probably a low-power device and is allowed up to that much by the standard, but it is more likely to take only about 20mA, leaving a bit more for any attached devices.

When in doubt, invest in one of these gizmos and measure it yourself.
 

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juiceme is offline juiceme
2014-08-22 , 08:52
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#46
Originally Posted by pichlo View Post
When in doubt, invest in one of these gizmos and measure it yourself.
Beautiful!

I was not aware a device like this exists. I'll have to get one of those for myself!
OTOH, it's not that difficult to make a breakout USB cable and insert a Fluke ammeter there in the loop...
 

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