Well, making a long story short:
http://yarchive.net/comp/linux/bitfields.html
Regards,
Christian.
Am 16.10.2014 um 16:14 schrieb Alex Deucher:
As part of the amdgpu transition, we are moving to using database
generated register and packet headers. We have a number of options
for formatting, some of which involve bitfields (don't worry there
will also be shift/mask style headers as well which is mainly what we
use in the code). I think these formats are cleaner for a number of
cases, however, as far as I know, C does not define the ordering of
bits within bitfields. That said, every compiler I've used seems to
do what you would expect. It makes coding a lot cleaner as less
error-prone in certain cases. Here are a couple of example of what
I'm talking about:
A register example:
union GRPH_SWAP_CNTL {
struct {
#if BIG_ENDIAN
unsigned int : 20;
unsigned int GRPH_ALPHA_CROSSBAR : 2;
unsigned int GRPH_BLUE_CROSSBAR : 2;
unsigned int GRPH_GREEN_CROSSBAR : 2;
unsigned int GRPH_RED_CROSSBAR : 2;
unsigned int : 2;
unsigned int GRPH_ENDIAN_SWAP : 2;
#else
unsigned int GRPH_ENDIAN_SWAP : 2;
unsigned int : 2;
unsigned int GRPH_RED_CROSSBAR : 2;
unsigned int GRPH_GREEN_CROSSBAR : 2;
unsigned int GRPH_BLUE_CROSSBAR : 2;
unsigned int GRPH_ALPHA_CROSSBAR : 2;
unsigned int : 20;
#endif
} bitfields, bits;
unsigned int u32All;
signed int i32All;
float f32All;
};
A packet example:
typedef union PM4_TYPE_3_HEADER
{
struct
{
#if BIG_ENDIAN
unsigned int type : 2; ///< packet identifier. It should
be 3 for type 3 packets
unsigned int count : 14;///< number of DWORDs - 1 in the
information body.
unsigned int opcode : 8; ///< IT opcode
unsigned int reserved1 : 6; ///< reserved
unsigned int shaderType: 1; ///< 0: Graphics, 1: Compute Shader
unsigned int predicate : 1; ///< predicated version of packet when set
#else
unsigned int predicate : 1; ///< predicated version of packet when set
unsigned int shaderType: 1; ///< 0: Graphics, 1: Compute Shader
unsigned int reserved1 : 6; ///< reserved
unsigned int opcode : 8; ///< IT opcode
unsigned int count : 14;///< number of DWORDs - 1 in the
information body.
unsigned int type : 2; ///< packet identifier. It should
be 3 for type 3 packets
#endif
};
unsigned int u32All;
} PM4_TYPE_3_HEADER;
//--------------------MEM_SEMAPHORE--------------------
enum MEM_SEMAPHORE_signal_type_enum {
signal_type_mem_semaphore_SIGNAL_TYPE_INCREMENT_0 = 0,
signal_type_mem_semaphore_SIGNAL_TYPE_WRITE_1 = 1 };
enum MEM_SEMAPHORE_client_code_enum { client_code_mem_semaphore_CP_0 =
0, client_code_mem_semaphore_CB_1 = 1, client_code_mem_semaphore_DB_2
= 2, client_code_mem_semaphore_RESERVED_3 = 3 };
enum MEM_SEMAPHORE_sem_sel_enum {
sem_sel_mem_semaphore_SIGNAL_SEMAPHORE_6 = 6,
sem_sel_mem_semaphore_WAIT_SEMAPHORE_7 = 7 };
typedef struct _PM4_MEM_SEMAPHORE
{
union
{
PM4_TYPE_3_HEADER header; ///header
unsigned int ordinal1;
};
union
{
struct
{
#if BIG_ENDIAN
unsigned int address_lo:29;
unsigned int reserved1:3;
#else
unsigned int reserved1:3;
unsigned int address_lo:29;
#endif
} bitfields2;
unsigned int ordinal2;
};
union
{
struct
{
#if BIG_ENDIAN
MEM_SEMAPHORE_sem_sel_enum sem_sel:3;
unsigned int reserved4:3;
MEM_SEMAPHORE_client_code_enum client_code:2;
unsigned int reserved3:3;
MEM_SEMAPHORE_signal_type_enum signal_type:1;
unsigned int reserved2:3;
unsigned int use_mailbox:1;
unsigned int address_hi:16;
#else
unsigned int address_hi:16;
unsigned int use_mailbox:1;
unsigned int reserved2:3;
MEM_SEMAPHORE_signal_type_enum signal_type:1;
unsigned int reserved3:3;
MEM_SEMAPHORE_client_code_enum client_code:2;
unsigned int reserved4:3;
MEM_SEMAPHORE_sem_sel_enum sem_sel:3;
#endif
} bitfields3;
unsigned int ordinal3;
};
} PM4MEM_SEMAPHORE, *PPM4MEM_SEMAPHORE;
Are there any strong objections to these sorts of structures?
Thanks,
Alex
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