For reasons of efficiency it is sometimes necessary to embed simple assembly language instructions in-line, for example to enable and disable interrupts. If this is necessary, then it is recommended that it be achieved by using macros, or for C99, inline functions.

Encapsulating assembly language is beneficial because:

It improves readability;
The name, and documentation, of the encapsulating macro or function makes the intent of the assembly language clear;
All uses of assembly language for a given purpose can share the same encapsulation which improves maintainability;
The assembly language can easily be substituted for a different target or for purposes of static analysis.

Note: the use of in-line assembly language is an extension to standard C, and therefore violates Rule 1.2.

Example

#define NOP asm("    NOP")

MISRA-C 2004 Rule 2.1 (required): Assembly language shall be encapsulated and isolated

[Unspecified 11]

Where assembly language instructions are required it is recommended that they be encapsulated and isolated in either (a) assembler functions, (b) C functions or (c) macros.

For reasons of efficiency it is sometimes necessary to embed simple assembly language instructions in-line, for example to enable and disable interrupts. If it is necessary to do this for any reason, then it is recommended that it be achieved by using macros.

Note that the use of in-line assembly language is an extension to standard C, and therefore also requires a deviation against Rule 1.1.

Example

#define NOP asm("   NOP")

MISRA C++ 2008 Rule 7—4—3 (required): Assembly language shall be encapsulated and isolated.

Rationale

Ensuring that assembly language code is encapsulated and isolated aids portability.

Where assembly language instructions are needed, they shall be encapsulated and isolated in either assembler functions or C++ functions.

Example

void Delay ( void )
{
   asm ( "NOP" ); // Compliant
}
void fn ( void )
{
   DoSomething ( );
   Delay ( ); // Assembler is encapsulated
   DoSomething ( );
   asm ( "NOP" ); // Non-compliant
   DoSomething ( );
}