Worth Read #24

Q: The circle can rotate clockwise and back. Use minimum hardware to build
a circuit to indicate the direction of rotating. 
A: 2 sensors are required to find out the direction of rotating. They are placed like at the drawing. One of them is connected to the data input of D flip-flop, and the second one - to the clock input. If the circle rotates the way clock sensor sees the light first while D input (second sensor) is zero - the output of the flip-flop equals zero, and if D input sensor "fires" first - the output of the flip-flop becomes high, please go through the link frenz....

enjoy...

Worth Read #23

Critical Frequency (in terms of radio- electronics)

The critical frequency is an important figure that gives an indication of the state of the ionosphere and the resulting HF propagation. It is obtained by sending a signal pulse directly upwards. This is reflected back and can be received by a receiver on the same site as the transmitter. The pulse may be reflected back to earth, and the time measured to give an indication of the height of the layer. As the frequency is increased a point is reached where the signal will pass right through the layer, and on to the next one, or into outer space. The frequency at which this occurs is called the critical frequency.

The equipment used to measure the critical frequency is called an ionosonde. In many respects it resembles a small radar set, but for the HF bands. Using these sets a plot of the reflections against frequency can be generated. This will give an indication of the state of the ionosphere for that area of the world

Worth Read #22

main()
{
float me = 1.1;

double you = 1.1;
if(me==you)
printf("I love U");
else
printf("I hate U");
}

Answer:
I hate U

Explanation:
For floating point numbers (float, double, long double) the values cannot be predicted
exactly. Depending on the number of bytes, the precession with of the value represented varies. Float
takes 4 bytes and long double takes 10 bytes. So float stores 0.9 with less precision than long double.
Rule of Thumb:
Never compare or at-least be cautious when using floating point numbers with relational
operators (== , >, <, <=, >=,!= ) .

Worth Read #21

punter pointer! :D

main()
{

char s[ ]="man";
int i;
for(i=0;s[ i ];i++)
printf("\n%c%c%c%c",s[ i ],*(s+i),*(i+s),i[s]);
}

Answer:
mmmm
aaaa
nnnn

Explanation:
s[i], *(i+s), *(s+i), i[s] are all different ways of expressing the same idea. Generally array
name is the base address for that array. Here s is the base address. i is the index number/displacement from
the base address. So, indirecting it with * is same as s[i]. i[s] may be surprising. But in the case of C it is
same as s[i].

Worth Read (and answer) #20

49 most important interview questions... 

1. What are static variables?
2. What are volatile variables?
3. What do you mean by const keyword ?

4. What is interrupt latency?
5. How you can optimize it?
6. What is size of character, integer, integer pointer, character pointer?
7. What is NULL pointer and what is its use?
8. What is void pointer and what is its use?
9. What is ISR?
10.What is return type of ISR?
11.Can we use any function inside ISR?
12.Can we use printf inside ISR?
13.Can we put breakpoint inside ISR?
14.How to decide whether given processor is using little endian format or big endian format ?
15.What is Top half & bottom half of a kernel?
16.Difference between RISC and CISC processor.
17.What is RTOS?
18.What is the difference between hard real-time and soft real-time OS?
19.What type of scheduling is there in RTOS?
20.What is priority inversion?
21.What is priority inheritance?
22.How many types of IPC mechanism you know?
23.What is semaphore?
24.What is spin lock?
25.What is difference between binary semaphore and mutex?
26.What is virtual memory?
27.What is kernel paging?
28.Can structures be passed to the functions by value?
29.Why cannot arrays be passed by values to functions?
30.Advantages and disadvantages of using macro and inline functions?
31.What happens when recursion functions are declared inline?
32.#define cat(x,y) x##y concatenates x to y. But cat(cat(1,2),3) does not expand but gives
preprocessor warning. Why?
33.Can you have constant volatile variable? Yes, you can have a volatile pointer?
34.++*ip increments what? it increments what ip points to
35.Operations involving unsigned and signed — unsigned will be converted to signed
36.malloc(sizeof(0)) will return — valid pointer
37.main() {fork();fork();fork();printf("hello world"); } — will print 8 times.
38.Array of pts to functions — void (*fptr[10])()
39.Which way of writing infinite loops is more efficient than others? there are 3ways.
40.Who to know whether system uses big endian or little endian format and how to convert
among them?
41.What is forward reference w.r.t. pointers in c?
42.How is generic list manipulation function written which accepts elements of any kind?
43.What is the difference between embedded systems and the system in which RTOS is running?
44.How can you define a structure with bit field members?
45.How do you write a function which takes 2 arguments - a byte and a field in the byte and
returns the value of the field in that byte?
46.Which parameters decide the size of data type for a processor ?
47.What is job of preprocessor, compiler, assembler and linker ?
48.What is the difference between static linking and dynamic linking ?
49.How to implement a WD timer in software ?

ENJOYYYYYYYYYYYYYY.................

Worth Read #19

Obscure syntax 

C allows some appalling constructs. Is this construct legal, and if so what does this code do? 

int a = 5, b = 7, c;
c = a+++b;
This question is intended to be a lighthearted end to the quiz, as, believe it or not, this is perfectly legal syntax. The question is how does the compiler treat it? Those poor compiler writers actually debated this issue, and came up with the "maximum munch" rule, which stipulates that the compiler should bite off as big (and legal) a chunk as it can. Hence, this code is treated as:

c = a++ + b;
Thus, after this code is executed, a = 6, b = 7, and c = 12.
If you knew the answer, or guessed correctly, well done. If you didn't know the answer then they wouldn't consider this to be a problem. they find the greatest benefit of this question is that it is good for stimulating questions on coding styles, the value of code reviews, and the benefits of using lint.

Enjoy :)

Worth Read #18

Typedef 
Typedef is frequently used in C to declare synonyms for pre-existing data types. It is also possible to use the preprocessor to do something similar. For instance, consider the following code fragment: 

#define dPS struct s *

typedef struct s * tPS;
The intent in both cases is to define dPS and tPS to be pointers to structure s. Which method, if any, is preferred and why?
This is a very subtle question, and anyone who gets it right (for the right reason) is to be congratulated or condemned ("get a life" springs to mind). The answer is the typedef is preferred. Consider the declarations:

dPS p1,p2;
tPS p3,p4;
The first expands to:

struct s * p1, p2;
which defines p1 to be a pointer to the structure and p2 to be an actual structure, which is probably not what you wanted. The second example correctly defines p3 and p4 to be pointers.