Embedded C

Storage class

Static

1. Static Local Variables

   Value is retained between function calls

2. Static Global Variables & Static Functions

   Scope is limited to the file in which it is declared

Extern

The extern keyword is used to declare a variable or function that is defined in another file

Pointer

// p is a pointer to a constant type uint8_t variable
uint8_t const \*p = (uint8_t\*)0x1234;
// p is a constant pointer to a uint8_t variable
uint8_t \*const p = (uint8_t\*)0x1234;
// p is a constant pointer pointing constant data of type uint8_t
uint8_t const \*const p = (uint8_t\*)0x1234;

Structure

To reduce padding

• Group similar types together
• Order by size, largest first

Memory Sections

+------------------+
|   Text Segment   |  // Code and read-only data
+------------------+
| Initialized Data |  // Global and static variables with initial values
+------------------+
| Uninitialized    |  // Global and static variables without initial values (BSS)
| Data (BSS)       |
+------------------+
|      Heap        |  // Dynamic memory allocation (grows upwards)
+------------------+
|      Stack       |  // Local variables, function parameters (grows downwards)
+------------------+

Floating Point

• Floating-point types (float, double, long double) are used to represent real numbers in Embedded C.
• Consider the performance, memory usage, and precision when using floating-point operations in embedded systems.
• Ensure that your microcontroller and compiler support floating-point arithmetic.

#include <stdio.h>
 
int main() {
    float a = 3.14f;
    double b = 3.141592653589793;
    long double c = 3.14159265358979323846L;
 
    printf("float: %f\n", a);
    printf("double: %lf\n", b);
    printf("long double: %Lf\n", c);
 
    return 0;
}

MCDC Coverage

Ensures that each condition in a decision has been tested to independently affect the decision’s outcome. MCDC can be covered by normal gcov/lcov tools if the conditions in code only written in tree like format.

typedef struct vs struct

• struct: Requires the struct keyword for each declaration. Useful for emphasizing the structure type.
• typedef struct: Creates an alias for the structure type, making the code cleaner and easier to read. Commonly used in libraries and APIs.

Access level of the processor

• Default run in previleged mode