CODEWITHSUNDEEP
cmacros
debevv
debevv

Reputation: 143

Reference C #define from runtime parameters

I have a list of #define that describes a set of addresses:

#define DMA1_Stream0        ((DMA_Stream_TypeDef *) DMA1_Stream0_BASE)
#define DMA1_Stream1        ((DMA_Stream_TypeDef *) DMA1_Stream1_BASE)
#define DMA1_Stream2        ((DMA_Stream_TypeDef *) DMA1_Stream2_BASE)
#define DMA1_Stream3        ((DMA_Stream_TypeDef *) DMA1_Stream3_BASE)

(this is from a CMSIS header) and a function that should use one of them depending on the given parameters like:

void initDMAStream(uint8_t controller, uint8_t stream)
{
    DMA[controller]_Stream[stream]->CR = 0xdadadada;
    // etc...
}

I tried using a macro like

#define DMA_STREAM(c, s) DMA ## c ## _Stream ## s

but it's not working because it will replace c and s with the names of the function parameters, not with their values.

Is there some way to do this in C?

Upvotes: 0

Views: 77

Answers (1)

Nicu Stiurca
Nicu Stiurca

Reputation: 8677

It looks like you are trying to mix run-time and compile-time evaluation in an unholy way. In particular, you are trying to use run-time information at compile time.

You can make this work by throwing the compile-time constants into an array, and indexing into it at run-time. For example, set up the array as

DMA_Stream_TypeDef * DMAstreams[][4] = { {DMA0_Stream0, DMA0_Stream1, DMA0_Stream2, DMA0_Stream3}, {DMA1_Stream0, DMA1_Stream1, DMA1_Stream2, DMA1_Stream3}, // ... };

and access it with

DMAstreams[controller][stream]

at run-time.

Upvotes: 1

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