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USB OTG without external power supply

25th February 2014, 05:48 PM   |  #1  
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Hello! Most devices like Nexus 4 or our S4 Mini have problems with USB OTG functionality - they can't provide power to connected device. When I was browsing through some system folders, I've found a directory /d/regulator/8921_usb_otg/8921_usb_otg. In this directory, I can see voltage values, but I'm not able to edit them. Can someone help me how to edit max_uV and min_uV files? Folder called "enable" can be changed to 1, but other folders no.
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Last edited by lipalok; 8th April 2014 at 07:16 PM.
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25th February 2014, 07:38 PM   |  #2  
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Quote:
Originally Posted by lipalok

Hello! Most devices like Nexus 4 or our S4 Mini have problems with USB OTG functionality - they can't provide power to connected device. When I was browsing through some system folders, I found a directory /d/regulator/8921_usb_otg/8921_usb_otg. In this directory, I can see voltage values, but I'm not able to edit them. Can someone help me how to edit max_uV and min_uV files? Folder called "enable" can be changed to 1, but other folders no.

Use ES file explorer, tap the world icon on the top left, Tools, Root Explorer OFF To on, give root permissions, after tap on root explorer again (On the Word now, not on the "ON" button and tap Mount System R/W On the menu that will appear.

Sorry for my english
26th February 2014, 09:49 AM   |  #3  
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Quote:
Originally Posted by 96DANGER96

Use ES file explorer, tap the world icon on the top left, Tools, Root Explorer OFF To on, give root permissions, after tap on root explorer again (On the Word now, not on the "ON" button and tap Mount System R/W On the menu that will appear.

Sorry for my english

From the screenshots he has posted, the folder is already in R/W mode
@lipalok

All the files in that folder have readonly atttibutes set r--r--r--. Try copying the files to some folder in the sdcard, change them, then move them back to the folder and set the same permissions as before.
Last edited by gladson1976; 26th February 2014 at 09:52 AM.
26th February 2014, 10:19 AM   |  #4  
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Quote:
Originally Posted by gladson1976

From the screenshots he has posted, the folder is already in R/W mode
@lipalok

All the files in that folder have readonly atttibutes set r--r--r--. Try copying the files to some folder in the sdcard, change them, then move them back to the folder and set the same permissions as before.

It didn't work I'm not able to copy them. Try it on your phone, please.
Last edited by lipalok; 26th February 2014 at 10:26 AM.
26th February 2014, 02:08 PM   |  #5  
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Quote:
Originally Posted by lipalok

It didn't work I'm not able to copy them. Try it on your phone, please.

I've attached 8921_usb_otg folder with all the files here, use es file manager with root permissions to replace them.
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26th February 2014, 04:00 PM   |  #6  
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Quote:
Originally Posted by 96DANGER96

I've attached 8921_usb_otg folder with all the files here, use es file manager with root permissions to replace them.

What values should I use?

UPDATE: After trying it, copy task failed
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Last edited by lipalok; 26th February 2014 at 04:20 PM.
27th February 2014, 03:48 AM   |  #7  
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Quote:
Originally Posted by lipalok

It didn't work I'm not able to copy them. Try it on your phone, please.

Sorry about that. I don't have a S4 Mini (yet). Planning to get one next week.
23rd March 2014, 02:42 PM   |  #8  
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Hi guys!
The "file" you are trying to edit is not a file, but sysfs node.

To set or read a value you do this:
adb shell
su
cd /d/regulator/8921_usb_otg
echo 1 > enable
etc...

try to set max_uV to USB voltage which is 5V, it's in uV so:
echo 5000000 > max_uV
26th February 2014, 09:59 AM   |  #9  
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Quote:
Originally Posted by lipalok

Hello! Most devices like Nexus 4 or our S4 Mini have problems with USB OTG functionality - they can't provide power to connected device. When I was browsing through some system folders, I found a directory /d/regulator/8921_usb_otg/8921_usb_otg. In this directory, I can see voltage values, but I'm not able to edit them. Can someone help me how to edit max_uV and min_uV files? Folder called "enable" can be changed to 1, but other folders no.

I'll check my GS2 that has these values and write here...
5th April 2014, 07:43 PM   |  #10  
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good news. would be interesting to find out if another phone is using the same port and has otg, so a dev could take a look into kernel source of that device.
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