Function level optimization

Jon Zarate

Expert 1190 points

I need to perform a delay without interrupts, so I have an empty loop with just a counter.

The optimization erases the functions since it's useless, but I need it.

I don't want to turn off all the optimization of the project.

The attribute __attribute__((optimize("-Ooff")) can't be used in the TI compiler (mspgcc).

Source, page 119, 5.16.2, Function Attributes.

Any idea on how to approach this ? A #pragma maybe ?

Thanks.

over 7 years ago

0 George Mock over 7 years ago

TI__Guru**** 232670 points

Use the __delay_cycles intrinsic. Please search for it in the MSP430 compiler manual.

Thanks and regards,

-George

0 Jon Zarate over 7 years ago in reply to George Mock

Expert 1190 points

How does __delay_cycles work ? Does it use a Timer ?

I can't use any type of interrupts (project limitation).

Apart from that, can you think of any other way ? (I will need to explain why I used that way, so all information is appreciated).

0 Archaeologist over 7 years ago in reply to Jon Zarate

TI__Guru* 84225 points

It implements a loop in the assembly code that does nothing. Have the compiler keep the assembly code and see for yourself.

0 Chester Gillon over 7 years ago in reply to Jon Zarate

Guru 92251 points

Jon Zarate said:
Does it use a Timer ?

__delay_cycles doesn't use a timer, but generates code to generate a delay assuming zero-wait states.

If you are using MSP430 FRAM based device and the __delay_cycles code is running from FRAM with wait-states enabled there may be a potential for the actual delay may be longer if the code for the delay doesn't fit in the FRAM cache.

[I haven't investigated the accuracy of __delay_cycles in MSP430 FRAM devices with wait states enabled, but have seen longer delays than requested in ARM devices with wait states - see https://e2e.ti.com/support/development_tools/code_composer_studio/f/81/t/410025]

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Function level optimization