Bit manipulations good practices

Question

As a beginner C programmer, I am wondering, what would be the best easy-to-read and easy-to-understand solution for setting control bits in a device. Are there any standards

Answer 1

The old-school C way is to define a bunch of bits:

#define WORD  0x04
#define GO    0x08
#define I_EN  0x10
#define LEEN  0x80

Then your initialization becomes

DMA_base_ptr[DMA_CONTROL_OFFS] = WORD | GO | LEEN;

You can set individual bits using |:

DMA_base_ptr[DMA_CONTROL_OFFS] |= I_EN;

You can clear individual bits using & and ~:

DMA_base_ptr[DMA_CONTROL_OFFS] &= ~GO;

You can test individual bits using &:

if(DMA_base_ptr[DMA_CONTROL_OFFS] & WORD) ...

Definitely don't use bitfields, though. They have their uses, but not when an external specification defines that the bits are in certain places, as I assume is the case here.

See also questions 20.7 and 2.26 in the C FAQ list.