Array initialization

Basic initialization

int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };

other syntax 

int myArray[10] = { [4] = 5, [2] = 5 }; 

is equivalent to

int myArray[6] = { 0, 0, 5, 0, 5, 0 };

initialize a range of elements to the same value

int myArray[10] = {[0 ... 9] = 5};

Elements with missing values will be initialized to 0:

int myArray[10] = { 1, 2 }; // initialize to 1,2,0,0,0...

So this will initialize all elements to 0:

int myArray[10] = { 0 }; // all elements 0(only for Zero initial)

Remember that objects with static storage duration will initialize to 0 if no initializer is specified:

static int myArray[10]; // all elements 0

In C++, an empty initialization list will also initialize every element to 0. This is not allowed with C:

int myArray[10] = {}; // all elements 0 in C++

And that "0" doesn't necessarily mean "all-bits-zero", so using the above is better and more portable than memset(). (Floating point values will be initialized to +0, pointers to null value, etc.)
Reference
[1] http://stackoverflow.com/questions/201101/how-to-initialize-an-array-in-c
[2] https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
[3] http://www.lemoda.net/c/array-initialization/ (experiment)

Inline Functions versus Macros

add my commend into the content

1. Inline functions follow all the protocols of type safety enforced on normal functions.
• more safe then the macro, especially, for the type defination.
• for the type check, macro is checked by prepocessor, and inline functions is checked by compilar.
2. Inline functions are specified using the same syntax as any other function except that they include the inline keyword in the function declaration.
• only difference is keyword “inline”
3. Expressions passed as arguments to inline functions are evaluated once. In some cases, expressions passed as arguments to macros can be evaluated more than once.
• more variable for arguments
4. There is no risk if called multiple times. But there is risk in macros which can be dangerous when the argument is an expression.
5. functions can include multiple lines of code without trailing backlashes.
6. functions have thier own scope for variables and they can return a value.
7. debuging

Reference

[1] http://msdn.microsoft.com/en-us/library/bf6bf4cf.aspx

[2] http://www.thegeekstuff.com/2013/04/c-macros-inline-functions/

function and function-like macro

if we use the same name for those things. avoid the prepocessor will expand the function first, we usaully add parenthese to prevent.

simple example

#include <stdio.h>
#define test(x) __test(x)
#define __test(x) printf("\n%d\n", x + 1);

int test(int x);
#undef test

int main()
{
    test(1);
}
int (test)(int x)
{
    printf("\n%d\n", x);
}

Referemce

http://stackoverflow.com/questions/13600790/what-do-the-parentheses-around-a-function-name-mean

samba

 

smbpasswd

-a add new accout

-U change password

Reference

[1] https://www.samba.org/samba/docs/man/manpages/smbpasswd.8.html

CRP

CRP(Code read protection) is a way to avoid someone to get code from flash.

CRP

In C, Keyword “static”

#include <stdio.h>
 
int global_var;        //statically allocated as a global variable
static int static_var; //statically allocated but only accessible within file
 
void my_function(void){
     static int my_static = 0; //statically allocated, accessible within my_function
     int my_stack = 0; //allocated on the stack
 
     printf("my_static:%d, my_stack:%d\n", my_static, my_stack);
     my_stack++;
     my_static++;
}

Answer: 

my_static:0, my_stack:0
my_static:1, my_stack:0
my_static:2, my_stack:0
my_static:3, my_stack:0
my_static:4, my_stack:0

Reference

[1] http://coactionos.com/embedded%20design%20tips/2013/10/18/Tips-RAM-Flash-Usage-in-Embedded-C-Programs/

RAM/Flash Usage in Embedded C Programs

 

Read-only memory(Flash)

Data Section

int data_variable = 500;

Read-only date

constant

const int read_only_variable = 2000;

Text(code)

“literal pool” may in the function.

void my_function(void){
     int x;
     x = 200;
     printf("X is %d\n", x);
}

Read-Write Data(RAM)

Data section

int data_var = 500; //require flash memory to stored.

BSS section

int bss_var0;
int bss_var1 = 0;

//doesn’t need require flash memory to stored.

Heap section

static int static_var;

buffer = malloc(512);

Stack section

int my_function(int a, int b, int c, int d)

Reference

[1] http://coactionos.com/embedded%20design%20tips/2013/10/18/Tips-RAM-Flash-Usage-in-Embedded-C-Programs/

Assembly command note

 

The syntax of MOV can also be more complex as the following examples show.^[7]

MOV EAX, [EBX]	  ; Move the 4 bytes in memory at the address contained in EBX into EAX
MOV [ESI+EAX], CL ; Move the contents of CL into the byte at address ESI+EAX

 

Reference

[1] http://en.wikipedia.org/wiki/Assembly_language

Time Stamp

for keil compilar environment, they had a defination for time stamp, therefore we could use that to be a release note for product purpose.

how to use?

printf("%s %s",__DATE__,__TIME__);

or you could assign memory for them.

U8 KC_DATA Datestring[sizeof(__DATE__)];
U8 KC_DATA Timestring[sizeof(__TIME__)];


memcpy(Datestring, &__DATE__, sizeof(__DATE__));
memcpy(Timestring, &__TIME__, sizeof(__TIME__));

 

Reference

[1] http://www.keil.com/forum/2789/display-time-and-date/

compilar a specific memory address for variable and function

Compiler-specific Features [4]

function attributs

assign a section for place function code [1,2]

Variable attributs

locating a variable at absolute memory address [3]

Reference

[1] http://www.keil.com/support/man/docs/armccref/armccref_Cacbgief.htm

[2] http://www.keil.com/forum/13875/-at-for-function-address/

[3] http://www.keil.com/support/docs/2829.htm

[4] http://www.keil.com/support/man/docs/armccref/armccref_chdfijae.htm