Qualcomm Interview Question for Software Engineer / Developers






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ISR's should not invoke functions which may cause ``blocking'' of the caller. An ISR must not perform I/O, A call to a device driver may block the system if the caller needs to wait for the device.

- Anonymous October 16, 2008 | Flag Reply
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Nothing more than calling the respective sys_foo from the syscall table.

- XYZ October 29, 2008 | Flag Reply
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A real time example, There are three people sitting in front of white board, a pen placed with that white board. Now one person start writing on the board others has to wait until he finished, once he finished writing then he will replace that pen, now next person will get chance to start write on that board. similarly for other one. her only one pen is available so other can't start until he replace that pen.

- Vishnu December 11, 2008 | Flag Reply
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One should never sleep in an Interrupt handler. Things that might cause blocking/sleeping are:
1. Using semaphore to lock a shared data structure
2. Calling functions that might sleep
3. Allocating memory

Also one should not perform time consuming tasks in an ISR.

- Sandip July 31, 2009 | Flag Reply
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You can allocate memory in ISR at least in Linux. Use function get_free_pages(). If the memory is not available, it will return immediately and thus does not block.

- Anonymous November 30, 2010 | Flag


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