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[ARM] Trying to understand the Cube HAL library

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Prototype21

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Hey Guys,
I am new to edaboard and ARM microcontroller. I happened to encounter the following two macro definition in HAL library in STMCubeMX.

First:
Code: 
#define __HAL_DMA_GET_TC_FLAG_INDEX(__HANDLE__) \
(((uint32_t)((__HANDLE__)->Instance) == ((uint32_t)DMA1_Channel1))? DMA_FLAG_TC1 :\
 ((uint32_t)((__HANDLE__)->Instance) == ((uint32_t)DMA1_Channel2))? DMA_FLAG_TC2 :\
 ((uint32_t)((__HANDLE__)->Instance) == ((uint32_t)DMA1_Channel3))? DMA_FLAG_TC3 :\
 ((uint32_t)((__HANDLE__)->Instance) == ((uint32_t)DMA1_Channel4))? DMA_FLAG_TC4 :\
   DMA_FLAG_TC5)

Second:
Code: 
__HAL_DMA_CLEAR_FLAG(__HANDLE__, __FLAG__) (DMA1->IFCR = (__FLAG__))

In the c file, it called like

Code: 
__HAL_DMA_CLEAR_FLAG(hdma, __HAL_DMA_GET_TC_FLAG_INDEX(hdma));

I am little confused here. How can a macro behave like a function. Is it possible to pass __HAL_DMA_GET_TC_FLAG_INDEX(hdma) as a parameter to __HAL_DMA_CLEAR_FLAG. Whats happening here?
 

A macro will always be expanded to the corresponding text. It can be written with parameters (as in the '__HANDLE__' part here) which means it will substitute whatever text is in the macro invocation as part of the expansion.
For example:
Code: 
#define abc(d) d * 2
fred(abc(x));
will expand to
Code: 
fred(x * 2);
From this you should be able to see the answer to your second question: you are not passing the macro as a parameter, you will be passing the textual expansion of the macro - in this case it is an ugly nested ternary statement that will be evaluated at runtime and the result will be the parameter that is passed to the function.
Susan
 
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