Embedded C - Linux Device Driver - BSP - Interview Questions
C Questions
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1. Storage classes
2. const and volatile
3. How to allocate memory in c - malloc vs calloc
4. brk, sbark
5. Any other system call to allocate memory. mmap ; anonymous mapping
6. Memory barriers; Why are they required
7. Wild and dangling pointers
8. struct alignment and packing. Need of alignment
9. Pass by value and ref
10. Endianness
11. size of void pointer
12. What is thread safety
13. What is re-entrancy
14. far and near pointers
15. Verify if a number is a power of two
16. nth element from last in a linked list
OS Concepts
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1. Thrashing
2. Deadlock - example
3. MM - Segmentation, paging, swapping
4. Paging vs swapping
5. Different segments in a program
6. Does linux use segmentation
7. System boot sequence
8. What is DMA. Modes - cycle stealing/burst (blk transfer)/transparent
9. Cache coherency during dma. Which component handles it
Embedded Interview Questions:
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What part of kernel driver worked. Explain
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Difference between kernerl/user space
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How system call causes change from user to kernel space
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Which RTOS worked on. Difference between various OS/RTOS
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How to chose RTOS for a consumer product
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Measure of performance of OS. Define performance
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How to debug crash. Gdb
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What is object file, how its used in crash
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What are the various code optimization techniques used
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memory leak deduction and various ways of handling
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How to write own malloc call
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How to proceed if system is sluggish
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How to determine if some high prio task is hogging CPU
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How debug prints/system trace could help solve above issues
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Important things to look for in code reviews
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Experrience with Oscilloscope, logic analyzer, i2C sniffer
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Understanding of schematics
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Why driver code in not written in C++/Java
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How to debug while system is running
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Run Time optimization
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Estimate the requirement in BSP domain
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How to define the process of QNX/Arch delivery integration
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How many years of experience in BSP domain
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What part of kernel driver worked. Explain
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Difference between kernerl/user space
-
How system call causes change from user to kernel space
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Which RTOS worked on. Difference between various OS/RTOS
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How to chose RTOS for a consumer product
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Measure of performance of OS. Define performance
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How to debug crash. Gdb
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What is object file, how its used in crash
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What are the various code optimization techniques used
-
memory leak deduction and various ways of handling
-
How to write own malloc call
-
How to proceed if system is sluggish
-
How to determine if some high prio task is hogging CPU
-
How debug prints/system trace could help solve above issues
-
Important things to look for in code reviews
-
Experrience with Oscilloscope, logic analyzer, i2C sniffer
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Understanding of schematics
-
Why driver code in not written in C++/Java
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How to debug while system is running
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Run Time optimization
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Estimate the requirement in BSP domain
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How to define the process of QNX/Arch delivery integration
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How many years of experience in BSP domain
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what is repeate sequence in I2C?
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How this signal will look on CRO?
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How many lines required for SPI communication?
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Do you need to change Clock polarity and phase for SPI?
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Who has control of SPI clock?
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What is deadlock?
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How to come out of deadlock?
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what is difference between mutex and semaphore?
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Explain board bring up.
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What is the difference between inline and macro?
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Write program toreset bit in register if address of register is given
reset (int address, int bit)
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How do you implement malloc ?
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How to know size of memory allocated by malloc using pointer?
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What is the problem in following code
char * p = 'a';
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How to fix it?
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Explain cinit and bss section
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how will you verify I2C communication?How will you know if there was a software or hw problem?
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How will you know if the I2C lines are noisy?
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Have you worked in crash dump?
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How will you solve memory crash, what steps would you take if a crash occurs?
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Diff between mutex and semaphore? Can semaphore be used for data synchronisation purpose?
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Data sharing between ISR and threads?
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Whats the boot loading process from powerup? They wanted a detailed answer to this asking for detailed explanation for every step?
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what is NAND and NOR flash, diff between them?
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What execution in place?
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What monitoring tools have you used like I2C sniffer
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How many years of experience in BSP domain
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Details of performance related optimisation?
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Memory map of RAM
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Where do const variables get stored? (literal segment)
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Static, auto, etc
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Write a program to change endianness
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What is structure padding?
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Why does the compiler perform padding?
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How to send information over network? (structure packing)
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Declare an array of 10 integer pointers
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Volatile variable in-depth (definition, use case, impact, when to avoid, etc)
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Where does dynamic memory allocation get stored?
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What are the pros and cons of using dynamic memory allocation versus static memory allocation?
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If you had to allocate 1MB of memory that needs to be used for only a short time, which type of allocation would you use?
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Different types of schedulers (round robin, pre-emptive)
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Timeslice, jiffy
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Priority inversion, priority inheritance, priority ceiling
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Difference between semaphores & mutexes
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Write a program to implement memcopy.
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Optimize it such that it uses NO stack space at all
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How to handle situation when a program is too large for code space? (edit linker file)
1. Write a program to find little endian or Big endian?
2. Write a program to find the number of bit’s set in a given number?
3. Write a program to delete a node in linked list(Any kind of linked list)
4. Write a program for set clear toggle a bit and find the given bit is set or not?
5. Types of storage classes?
6. Explain each and every storage class? And where Register storage class variable will save when registers are full?
7. Static key word usage and limitations and scope and where it is usefull?
8. Extern key word and what is the use of extern and gloable keyword?
9. Why we need Extern when we have Global value to access throughout the program?
10. IPC Mechanism? Types of IPC?
11. Write a program for shared memory?
12. Difference between Mutex and semaphore?
13. Where to use mutex and semaphore?
14. Regarding Deadlock situation and how to avoid deadlocs?
15. Does Preemption is required if there is a deadlock situation?
16. What is critical section? What mechanism is required to lock the shared resource in threads?
17. Structure padding and use of structure bit fields and how is save in memory location?
18. Is it possible to declare a function in structure?
19. How we can declare if we want?
20. What is volatile keyword? And where we can use?
21. Does synchronization technics are required for Volatile variable?
22. How you will analyze a crash without having any info (Kernel crash)?
23. Which are the information required to analyze crash?
24. Do you know panic and oops errors in kernel crash?
25. Major and minor number ?
26. write a character driver ?
1.What is the difference between Linux and RTOS ?and Reason why linux is not Real time?
2.How User space buffer can be accessed from kernel level and viceversa?
3.How to debug different threads in GDB?
4.Comfort level in Assembly level language?
5.What are the kernel structures and which kernel structure used in device driver development?
6.What is interrupt nesting, How IRQ priority handled?
7.What is SERDES?
8.How do you pass data between kernel modules?
9.What are different embedded design patters?
10. Memmory Mapping, synchronization Techiniques , Interrupts , Mutes , Interprocess_communication?
1.Explain camera sensor project
2.How frame buffers are allocated in camera sensor project
3.how to debug your driver if u had any buffer issues
4.Do u know about V4L2 layer
5.Have u faced any page faults in driver and how u will solve that issue?
6.How the data is transferred from camera sensor to LCD display
7.Do u know about IOCTL operations? and have they been used in your camera sensor project.
8.what is softirq and tasklet and work queues?
9.how you select the bottom half mechanism and what are the differences between them
10.what in interrupt context and process context
11.what is context switch
12.what are kernel synchronization techniques
13.Difference between sempahore and mutex and when u select the semaphore and mutex to use in your driver
14.what is process management
15.What is kernel thread?
16.what is pthread?
17.Do u know about IPC mechnanisms?
18.what is shared memory
19.Explain MMU in Linux
20.what is /proc entry and how it is useful
21.how the device files are created in linux
22.Difference between structure and union
23.what is function pointer and how it is used?
24.can i call a function using the address of that function through a point variable?
1.what is a device driver and write a simple driver
and explain what happens when an insmod is done an module
2.How will you insert a module statically in to linux kernel.
3.what are IPC mechanisms and explain d/f between all types with example scenario
4.explain the synchronization mechanisms
5.Explain about file system in linux kernel and how a kernel handles any file when it was created.
6.what is file descriptor and what informtion it contains in file descriptor
7.How do u see system messages and how do find the issues in system by reading the proc file system or dmsg queues or sysfs information.
8.what all kind of info is present in procfs.
9.when do u select the semaphore and a mutex and binary sempahore.
10.what is an interrupt and difference between exceptions and signals
11.How many types of signals are present in linux kernel.
1.How to create buffers in Kernel?
2.What is the difference b/w kmalloc and vmalloc
3.How buffer is copied to user level
4.Explain working of interrupts
5.Expalin about the projects mentioned in CV?
6.How to search for a specific nth-node in a given unknown number of nodes in a linked list?
7.How to determine the size of structure with out using "sizeof" operator?
8.What is memory leak
9.Fucntion Signature of registering Interrupt handler?aned Flags used while requesting IRQ?
10.Explain Shared memory ,Message Queue Synchronization techniquies in Linux
1.What is Function Pointer?
2.What is Call back function?
3.How Call Function works?
4.What is the clock frequency used in your I2C driver designed?
5.What is the start bit condition in I2C?
6.How I2C protocol works?
7.What are different speeds the I2C had?
8.What is the path of your driver inside kernel?
9.Can interrupts sleep?why?
10.Types of interrupts?
11.What are the function names for the driver you designed?
12.How the master knows what is the start condition ?
13.while in between I2C communication what happens if clocks happends to be dragged low which is not as per i2c standard?
14.What if the slave device is not responding or no acknowledge bit is sent by slave device?
15.What is the difference between kmalloc and vmalloc?
16.how to get physically contiguousness memory allocation if kmalloc is giving logical contiguousness allocations?
17.How do a driver get registered to kernel?
18.What actually happens while interrupt occurs exactly explain in terms of context switching
,what happens to the current running process?
19.As their no code written to do context saving when a interrupt happens in any of the functions then which is responsible in doing this context saving and switching context?
20.How "Make" is performed in compiling a module?
21.What is VOLATILE keyword?
22.Write a program to perform a string copy without using string library functions?
1. What is your role in J6 board bring-up
2. How you initialized EMMC in J6 board
3. What are the difference between EMMC version V1 and V2?
4. Any board bring-up sequence?
5. How to find the given number is power of 2?(Explain the logic how N & N-1)
6. Set a bit / Clear a bit / Toggle a bit?
7. Thread related Question?
8. Write a program for PWM using 2 threads and both the threads should start at same time?
a. (1st thread square wave 0 1 0 1 0 1 0 1 0)
b. (2nd thread square wave 00 11 00 11 00 11 00)
9. Regarding memory speed for file transfer.
Requirement:1. Having 2000 files with 6MB size each
2. Time is 2 min
How much speed we need to transfer the data to copy the complete files into emmc/ any other?
10. What are the difference between SPI and I2C ?
11. What are the different speeds in I2C and explain the number of slaves connection and how the address formation will be?
12. What is the maximum speed of SPI?
13. How to find the given linked list is palindrome or not? (logic is required)
14. How many loops are required to find the given linked list is Palindrome or not?
15. Explain your project architecture and where is your contribution?
1. What are types of ARM exceptions
http://osnet.cs.nchu.edu.tw/powpoint/Embedded94_1/Chapter%207%20ARM%20Exceptions.pdf
2. What is data aboard,do you know this,which ARM exception does this comes in to.
3. How an exception was raised when encountered any mallicious code
4. How the malloc internally work
5. When an unallocated pointer is derefrenced ,who will check that this is invailid instructoin.
6. Does the translations ,page tables ,virtual to physical translations all these are done in s/w or h/w
7. About voltile keyword,how volatile ensure that to read current updated value.
8. As you wokred in USB skeletion driver ,and about controller driver reads the deive descriptors.
9. How does controller driver reads the device descriptors if it via buffers,how does buffers are manged like any DMA things to be taken care,like cache.
1.Explain Boot up sequence and project which you worked?
2.Related to memory questions?
1.Do you know about the company?
2. 2.What is the use of emmc?
3. 3.How you will proceed to bring up the board?
4. 4.What all things you need when you are bring up the board?
5. 5.How you will bring up the board if we replace the original EMMC with our own EMMC?
6. 6.Do you know about how android will launch?
7. 7.Previous project related questions?
8. 8.How fastboot will work?
9. 9.How you will communicate with kernel if you don’t have access?
10.How you will debug the memory issues?
11.Do you know about flash memory?
12.What is the difference between NAND and NOR?
1.Write a macro to swap the nibbles in the word ?
Ex:0x1234 output:2143
2.Differance between macro & micro Kernel.
3.what you observed difference between QNX & Linux
4.Difference between Semaphore & Mutex
5.Write a programme to delete a given node number in Single linked list.
6.difference between processes and thread
7.diffrence b/w RTOS & GPOS
8.code base query :
Need the out put to be printed as 10.
int a=10;
main()
{
int a=20;
printf("%d",a);
}
1.What are the projects you worked and breif them
2.What is the difference between I2C & SPI
3.How will you chosse which protocal to be used on board communicaiton
4.How the communication difference b/w I2C & SPI
5.Sceanrio based query:
Had 4 sensors on board,which communicaiton you will chose to establish communicaiton b/w the sensors
6.Code base query:
what is the output.
main()
{
int *p= &a;
int a= 5;
printf("%d %d",*p,a);
}
7.Diff types of storage classes and details of each storage class
8.Detailed discussion on Static like storage ,default ,scope,life time.
9.Code based query:
what is the output.
main()
{
int a= 5;
int *p= &a;
printf("%d %d",*p,a);
}
main()
{
int a= 5;
int *p= &a;
*p++;
p--;
printf("%d %d",*p,a);
}
main()
{
int a= 5;
int *p= &a;
(*p)++;
p--;
printf("%d %d",*p,a);
}
10.
const volatile int *ptr;
*const volatile int ptr;
What is the diff .
11.
which pointer value we can modify.
const volatile int *ptr;
*const volatile int ptr;
12.different IPC mechanisms in QNX & Linux
13.Discussion on Shared Memory
14.Roles & Responsibilities in the project
15.What is greb loader
16.Embedded board Booting sequence
17.Diff b/w MLO & IPL.
18.Who will provide MBR and is it possible to modify.
19.Debugging techniques.
1.Why are you leaving the company, what are the reasons.
2. Write a macro to swap the nibbles in the word ?
Ex:0x1234 output:2143
3. Thread locked a resource ,before releasing the resource an Interrupt got triggred ,here interrupt is also using the same resource.
How will you handle this scenario.
4.Having Three resources and 10 Threads,
out of 10 ,3 threads acquired the resources, How will handle the reaming 7 threads
which thread has to come first to take the release resources
Which type of mechanism will you use for synchronization.
5.Diff b/w Semphore & Mutex /binaru sema & Mutex.Is it possible to use the counting semaphore for above scenario
6.What is Bit Binding in I2C protocol
7.Multimaster & single slave communication
m1: 0001 0000
m2: 0101 1010
m3: 0000 1111
Which master will acquire I2C Bus
8.What is i2c clock stretching
9.Is clock stretching is for Master or Slave in I2C protocol
10.How Multiple Threading is handled in single CPU.
1.Is const volatile possible ?
2.Where a const volatile variable is used?
3.What is booting sequence of linux?
4.Booting Sequence of a board ?
5.Why primary boot loader and secondary boot loader required?
6.What are types of boot loader?
7.How a user mode is transferred to kernel mode?
1.What memcopy do? implement your own memcopy function?with optimization(less usage of variables?)
2. int *i
char *c
void *v
tell me the sizes ?
sizeof(*i)
sizeof(i)
sizeof(*c)
sizeof(c)
sizeof(*v)
sizeof(v)
3.What is big endian and little endian?
implement a function changes the endians
4.what is cache coherence?
5.what is critical section?
6.what is protection mechanism?
7.Can a scheduler can be locked?
8.How are the compiler optimization techniques?
9.what is user space and kernel space?
10.Main Advantages and disadvantages of having separate user space and kernel space?
11.what is scheduler?
12.who schedules the scheduler?
13.At what frequency scheduler looks for threads/processes ready for schedule?
14.what is tick?
15.what actually does a system does in a tick?
16.what is DMA?
17.When cahche is enabled in a operating system ,DMA is enabled,how does DMA access the cache?
18.what is scheduler algoritham?
19.How interrupts are generated?
20. write a programe which includes the variables should cover all the segments ?
21.Local Const variables reside in which segment?
22.Global const variables reside in which segment?
23. How many stack will present?
24.does each processes has it own stack ?
25.does each thread has its own stack?
26.what is context switch ?
27.when their context switch from thread t1 To thread t2 where does the stack information of t1 gets stored?
28.What is advantage of virtual memory?
why not directly the physical address?
29.What is MMU?
30.what is a page fault?
31.What is instruction pipelining?
32.What is page write back?
1.Difference btwn Process and Thread
2.Diff btwn mutex & semaphore
3.Bit operations
4.C program for factorial, prime number with recursion
5.About Booting process
6.Questions on Pointers
7.What is Process preemption
8.About priority inversion & priority inheritance
9.How priority inheritance will work
10.structure padding
11.about #pragma
12.How to avoid re declaration of header files
13.About Jtag
1.How you Evaluate the Driver
2.about ISR, Interrupts
3.about Synchronization mechanism where you used in real time(examples)
4.what happen if you use mutex in ISR, how you over come with that problem
5.about memory mapped files
6.about linker scripts
7.what is re entrant function
8.what is module
9. IPC mechanism
10.toggle alternate bits
11.about function pointers
12.Advantages of func pointers
13.Advantages of call back functions
14. Declare a array of function pointer of taking two arguments
15. How to find little endian and big endian
1. Implement your own memcpy function and Error handling in memcpy
2. How you handle errors with the pointers
3. About dynamic and static memory
4.about malloc in depth
5. about Null pointer
6. how can you determine whether your memory is in protected or un-protected mode
7. About memory layout
8.How you will think while writing a program in optimized way
9.They will ask most of the question from memory in this round please study MMU well.
1.About volatile and use cases
2.Why the first two parameters are of type void in memcpy
3.Are #pragramas Gerneric or processor specific
4.Enabling & Disabling of interrupts
5.C program to swap every 2 bits in a 8 bit binary number.
6.Write a program to find how many bit to toggle in 2 binary numbers so that they become equal
a. program for to get the number of bits toggle in 2 binary numbers and toggle them to make the numbers equal
7. what is user mode and kernel mode
1.How you Decide the stack size for the function or thread.
2.Booting Sequence
3.About JTAG
4.Diff btwn SPI & I2C
5.Memory Layout
6.what is your strength
7.About Disassembly file(Memory map file)
8. About clock & timers
9.About Stack
1. Booting sequence in embedded systems
2. How to decrease the time of booting processes
3. What is the functionality of PROBE function
4.How to detect whether a device is not detected?
5.Own Malloc implementations
6.memcpy implementation
7.Find a word from string
8.How to find if their is in repeating node in linked list
9.For a given array gather all 1's to one side and 0's to one side.
10.In a given byte interchage pair of bits
11.Reverse linked list
12.Reverse string
13.Reverse a word in a string
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