Experimental Physics and
Industrial Control System

Eric Norum <[email protected]> · Tue, 28 Nov 2006 09:37:18 -0600

On Nov 28, 2006, at 9:23 AM, Marty Kraimer wrote:

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?

volatile should be used for all access to hardware registers.
volatile prevents compiler optimization.

Let's not get off on a tangent here. The problem Kay was describing

was one of structure padding, alignment, endianness when using a

structure to define the layout of hardware registers.

The issue on the table is that of compilers imposing their strict

aliasing rules, and what to do about that.

--
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