Hi I just started working on arm and I want to know Can we access or fetch a specific file( text,hex) from pendrive to arm controller to update controller firmware.
"I just started working on arm"
Maybe start here, then: www2.keil.com/.../learn
See also: http://www.keil.com/books/
Note that neither USB nor firmware update are beginner projects, though.
"Can we access or fetch a specific file( text,hex) from pendrive ..."
It has nothing specifically to do with ARM.
The USB functionality is provided by and proprietary to the particular chip manufacturer - so you will have to refer to the manufacturer's documentation for details of capabilities and restrictions.
But, yes, that would be a pretty standard thing to do with a USB Host - you will most probably find that the chip manufacturer provides (an) example(s) of doing exactly that.
Keil has middleware for doing that: www2.keil.com/.../middleware
Many 3rd-party middleware libraries are available.
"... to arm controller to update controller firmware"
Again, for the capabilities and restrictions of a particular chip to update its own firmware, you will have to refer to the manufacturer's documentation for that chip.
It is commonly supported - you will need a bootloader.
Sir can you suggest a controller for this problem statement