Real-Time Measurement and Control

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cRIO Linux RTOS usb power management


Hello Community,

I have a question about the power management of the cRIO usb ports.

I'm using the cRIO-9034 for the RT test bench and one of the requirement is to swith on/off the power of usb port to stress the external device.


I try to found the query that I can set to the command ligne in my RT app that will enable/disable or power on/off a usb port.

Actually I'm blocked because in the std Linux distribute I have an acces to this path : 

echo disable > /sys/bus/usb/devices/usb1/power/wakeup 

and then I can

echo on > /sys/bus/usb/devices/usb1/power/level       # turn on
echo suspend > /sys/bus/usb/devices/usb1/power/level  # turn off

 But the RTOS of my cRIO hasn't the "power" folder. I've tried to change the value of bMaxPower file (default it is 500mA) but I have no permissions.


Today I have no idea is it possible to do without any external device.

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Have you tried changing the permissions of the bMaxPower file? Try calling a chown with your user name on that file.

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Yes, I've tried it also. 

The problem is that the folder with bMaxPower (that influence the connection) not exists before the connection of the external device (port definition, etc). When I connect the device, It creates with the default parameters and when I change the value it is not instantly applied. If I restart the cRIO the default value is in place.


Finally I see that the Linux RTOS of cRIO has too much restriction, I will use the DO of the NI c-series module to drive directly the power of external device or to drive the external USB digital switch based on transistor switch.

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