Re: [avr-gcc-list] 12 Bit vars

[Michael Tsao]

> i have to store many values with a size of 12 Bits into the RAM. Is there a
> efficient way to do this with avr-gcc without wasting memory ?

Torsten,

These suggestions aren't specified to avr-gcc or AVR, but they might help. 
Experiment with this C construct:

struct DISK_REGISTER  {
    unsigned ready:1;
    unsigned error_occured:1;
    unsigned disk_spinning:1;
    unsigned write_protect:1;
    unsigned head_loaded:1;
    unsigned error_code:8;
    unsigned track:9;
    unsigned sector:5;
    unsigned command:5;
};

This tells the compiler the bit-width of each field, allowing it to pack the 
values into sub-byte spaces. I imagine you could pack two 12-bit values into 
three bytes, though I'm not sure how efficiently an 8-bit processor would be 
able to handle it.

Also, there is the packed #pragma, but I can't remember whether that's 
specific to Microsoft's C compiler or is also implemented in gcc.

Play around with these and see what you get. If you succeed, please tell the 
list!

Mike

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