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Compiler: clpru 2.2.1 does not recognize "#pragma pack" ?

Joierg Hoppe
Prodigy 150 points

Tool/software: TI C/C++ Compiler

Paltform is BeagleBone Black under Debian, I have a ARM/PRU project.

I've a struct in shared memory, to communicate with the ARM under Debian. I must  force the struct to same byte layout under ARM and under PRU, so I used "#pragma pack"

<codesnippet>
/***** start of shared structs *****/
#pragma pack(4)


typedef struct {
    uint32_t    addr ; // register 0..7
    uint32_t    bitmask ; // change only these bits in register
    uint32_t    val ; // value set/get.
} mailbox_buslatch_t;
</codesnippet>

But clpru says

"../common/mailbox.h", line 28: warning #163-D: unrecognized #pragma

According to manual, #pragma pack(4) is supported.

Full call line:

/home/joerg/retrocmp/dec/pdp11/UniBone/91_3rd_party/pru-c-compile/ti-cgt-pru_2.2.1//bin/clpru --include_path=/home/joerg/retrocmp/dec/pdp11/UniBone/91_3rd_party/pru-c-compile/ti-cgt-pru_2.2.1//include --include_path=/home/joerg/retrocmp/dec/pdp11/UniBone/91_3rd_party/pru-c-compile/pru-software-support-package/include --include_path=/home/joerg/retrocmp/dec/pdp11/UniBone/91_3rd_party/pru-c-compile/pru-software-support-package/include/am335x --include_path=../common -v3 -O3 --auto_inline --display_error_number --endian=little --hardware_mac=on --obj_directory=../bin-bbb --pp_directory=../bin-bbb -ppd -ppa --c_src_interlist --optimizer_interlist --absolute_listing -fe ../bin-bbb/pru1_main.object pru1_main.c
"../common/mailbox.h", line 28: warning #163-D: unrecognized #pragma

Thnaks fpr caring

Joerg Hoppe

  • 0
    TI__Guru**** 249390 points

    On PRU, all types are byte aligned.  See the section titled Data Types in the PRU compiler manual.  Therefore, all structs are packed, and there is no need for #pragma pack.  

    This is an error in the manual.  To have that addressed, I filed CODEGEN-4832 in the SDOWP system.  You are welcome to follow it with the SDOWP link below in my signature.

    Thanks and regards,

    -George

  • 0 in reply to George Mock
    Prodigy 150 points

    George,

    thanks for the quick answer. Chapter 6.2.1 makes it clear.

    I understand "always byte align" this way : In
    struct {
         uint8_t   a;
         uint32_t b;
    } testvar ;

    an access to testvar.b crosses a 32bit word border. This is a legal situation, but may be an performance issue.

    Can the CPU handle "word crossing" accesses easily, or should I have all struct members as uint32_t to avoid this situation?


    best regards,

    Joerg

  • 0 in reply to Joierg Hoppe
    TI__Guru**** 249390 points

    The information in this post is later found to be incorrect.  It is kept here only for continuity of the original thread.  -George

    Joierg Hoppe said:
    This is a legal situation, but may be an performance issue.

    We are not aware of any performance issues associated with non-aligned memory access.

    Thanks and regards,

    -George

  • 0 in reply to George Mock
    TI__Guru**** 249390 points

    Unfortunately, my last post is incorrect.  There is a performance penalty in some cases.

    With regard to accesses of these scalar types ...

    • char - no penalty
    • short, int, long, float, pointers - 1 cycle penalty if it crosses a 4-byte boundary
    • long long, double - 1 cycle penalty if it is not aligned on a 4-byte boundary

    At the present time, none of these data types are aligned.

    Thanks and regards,

    -George