ARM: Forcing halfword operation for (short *)?

[Toralf Lund]

Sigh... Another problem with my ARM setup, after trying to access some 
additional hardware... Seems like I still have a lot to learn about the 
fine level of control over I/O-operations...

Anyhow, the problem this time is the access size of a specific write 
operation. Consider the following function, which is a simplified 
version of one actually appearing in my application:

int eraseTest()
{
  volatile unsigned short *sector=(unsigned short *)0x10000000;
 
  *sector=(unsigned short )0x0030;
}

The code generated for this is (from 'objdump -d' output):

0801c938 <_eraseTest>:
 801c938:    e1a0c00d     mov    ip, sp
 801c93c:    e92dd800     stmdb    sp!, {fp, ip, lr, pc}
 801c940:    e24cb004     sub    fp, ip, #4    ; 0x4
 801c944:    e24dd004     sub    sp, sp, #4    ; 0x4
 801c948:    e3a03201     mov    r3, #268435456    ; 0x10000000
 801c94c:    e50b3010     str    r3, [fp, -#16]
 801c950:    e51b3010     ldr    r3, [fp, -#16]
 801c954:    e3a02000     mov    r2, #0    ; 0x0
 801c958:    e3a01030     mov    r1, #48    ; 0x30
 801c95c:    e5c32000     strb    r2, [r3]
 801c960:    e5c31001     strb    r1, [r3, #1]
 801c964:    e91ba800     ldmdb    fp, {fp, sp, pc}

This simply won't do. The problem? The data is stored via two strb 
operations, and it is absolutely essential that there is only one bus 
access. More generally, I need to have some more control over the actual 
access commands generated throughout my application.

So, why do I get two byte-accesses in this case? Why not one halfword 
operation? And is there any way to make sure "strh" is used instead?

- Toralf


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