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Tips on redefining a register bitfield in C


Tips on redefining a register bitfield in C

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Tips on redefining a register bitfield in C
Tag : c , By : Jonathan Bernard
Date : January 02 2021, 06:48 AM


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Register management tips


Tag : cpp , By : changke
Date : March 29 2020, 07:55 AM
wish helps you I don't think this is a problem of the machine, instead it is a problem of the programmer of the machine. What you can do(IMO) is just to provide the means to move the values of the registers into memory back and forth. Problem solved :)

Type of lvalue.bitfield when the underlying bitfield type is not int in C


Tag : c , By : yossi
Date : March 29 2020, 07:55 AM
I wish this helpful for you Someone drew my attention to the following program: , 6.7.2.1 paragraph 10 (emphasis added):

Is it possible to cast one type of bitfield to another type of bitfield with the same total number of bits?


Tag : c , By : user90210
Date : March 29 2020, 07:55 AM
wish of those help Anyone could tell if its possible to assign one type of bitfield to other type? With support of C90 compiler. , What you probably want here is a union:
typedef union {
    struct {
        //unsigned int:1;        // padding bit either here...
        unsigned int ERA:2;
        unsigned int destar:2;
        unsigned int srcar:2;
        unsigned int opcode:4;
        unsigned int grp:2;
        unsigned int dumy:3;
        //unsigned int:1;         // ...or here, depending on how you want to read it
    } cmd;
    uint16_t word;
} Cmd;

int main(int argc, const char * argv[]){
    Cmd cmd;
    cmd.cmd.grp = 2;
    printf("word=%u\n", cmd.word);
}

Does setting a 1-bit wide bitfield to 2 mean the bitfield is set or unset?


Tag : cpp , By : kakashi_
Date : March 29 2020, 07:55 AM
will be helpful for those in need [expr.ass]/6:

Union with bitfield gives unexpected value to bitfield members


Tag : cpp , By : chintown
Date : September 26 2020, 07:00 AM
seems to work fine Long story short - casting data via union is undefined behaviour, regardless of what you are doing. So it works and does not work just by accident. Only thing you are allowed to do with union is read the member you wrote to last time. You do anything other and your program is invalid.
EDIT:
struct {
    unsigned int a      : 12;
    unsigned int a_align: 20;
    unsigned int b      : 12;
    unsigned int b_align: 20;
    unsigned int c      : 12;
    unsigned int c_align: 20;
    unsigned int d      : 12;
    unsigned int d_align: 20;
    unsigned int unused : 16;
    unsigned int unused_align: 16;

};
unsigned mask12 = 0xFFF;//1 on first 12 least significant bits
unsigned a = data & mask12;
unsigned b = (data >> 12) & mask12;
unsigned c = (data >> 24) & mask12;
unsigned d = (data >> 36) & mask12;
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