Experimental Physics and
Industrial Control System

Eric Norum <[email protected]> · Tue, 28 Nov 2006 08:58:47 -0600

On Nov 28, 2006, at 8:33 AM, Kay-Uwe Kasemir wrote:

Hi:

Do I understand correctly that the most likely impact for EPICS

might be this type of code:

struct xyz_regs
{
    Word control;
    Word status;
    ...
}

void xyz_operate(char *vme_base)
{
    struct xyz_regs *xyz = (struct xyz_regs *) vme_base;

    xyz->control = 0x1234;
    if (xyz->status & 0x8000)
      ....
}

The mapping of C structures to hardware registers?
In that case, the compiler optimization of aliased pointers
isn't the only problem. There's also the structure padding,
memory alignment, and byte order that causes portability issues.

Isn't that best handled by performing register access

via routines like the vxWorks sysInByte(), sysInWord(), sysInLong

(), sysPciInLong(), ... ?

I'm more concerned about:
	all the casts between dbCommon and a particular record type

 casts between generic I/O buffer space and some particular data

representation

--
Eric Norum <[email protected]>
Advanced Photon Source
Argonne National Laboratory
(630) 252-4793

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System