ULP Advisor > Rule 8.1 Use 'static' & 'const' modifiers for local variables

ULP Advisor - Rule Table ULP 1.1 Ensure LPM usage ULP 2.1 Leverage timer module for delay loops ULP 3.1 Use ISRs instead of flag polling ULP 4.1 Terminate unused GPIOs ULP 5.1 Avoid processing-intensive operations: modulo, divide. ULP 5.2 Avoid processing-intensive operations: floating point ULP 5.3 Avoid processing-intensive operations: (s)printf() ULP 6.1 Avoid multiplication on devices without hardware multiplier ULP 6.2 Use MATHLIB for complex math operations ULP 6.3 Use Low Energy Accelerator (LEA) software library ULP 7.1 Use local instead of global variables where possible ULP 8.1 Use 'static' & 'const' modifiers for local variables ULP 9.1 Use pass by reference for large variables ULP 10.1 Minimize function calls from within ISRs ULP 11.1 Use lower bits for loop program control flow ULP 11.2 Use lower bits for port bit-banging ULP 12.1 Use DMA for large memcpy() calls ULP 12.1b Use DMA for potentially large memcpy() calls ULP 12.2 Use DMA for repetitive transfer ULP 13.1 Count down in loops ULP 14.1 Use unsigned variables for indexing ULP 15.1 Use bit-masks instead of bit-fields Let us know what you think! Feedback, suggestions & comments are welcome @ ULPAdvisorFeedback@list.ti.com

What it means

In an MSP430 C function, local variables without any modifiers are dynamically allocated upon each function call. This requires additional code & RAM space and the impact increases depending on the function call frequency. On the other hand, when declared as 'static', the variables are only generated once and remain available throughout the lifetime of the application. This minimizes the amount of code needed to re-allocate/re-initialize the variables every time the function is invoked. Alternatively, when the const modifier is used, the variable is stored as data in flash as part of the function, hence requiring no further re-allocation for each function entry.

Risks, Severity

Using local variables without 'static' or 'const' modifier requires additional code execution to reallocate & reinitialize the variables each time the function is invoked.

Why it is happening

The project code contains a function with local variables that are not but can be declared with the 'static' and/or 'const' modifiers.

Remedy

Use 'static' and/or 'const' modifiers for all applicable local variables (i.e. variables that do not change in values).

Code Example

void functionA(void) 
{ 
 static const variable1 = 0xFA;
 
 P1DIR = variable1;

} 

See the rest of the code examples for all MSP430 devices here!

More Resources

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