WLAN from SDIO to SPI: battle plan

[Andy Green]

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Somebody in the thread at some point said:

| By the way, it's really the "packed" that throws gcc into wild
| confusion. It can get even funnier:
|
| struct {
|     volatile int foo;
| } __attribute__((__packed__)) *p;
|
| void bar(void)
| {
|     p->foo = 0x42;
| }
|
| # arm-angstrom-linux-gnueabi-gcc -Wall -O -c -o foo.o foo.c
| # arm-angstrom-linux-gnueabi-objdump -d foo.o
|
| [...]
|    c:   e3a01000        mov     r1, #0  ; 0x0
|   10:   e3812042        orr     r2, r1, #66     ; 0x42
|   14:   e5c32000        strb    r2, [r3]
|   18:   e5d32001        ldrb    r2, [r3, #1]
|   1c:   e5c31001        strb    r1, [r3, #1]
|   20:   e5d32002        ldrb    r2, [r3, #2]
|   24:   e5c31002        strb    r1, [r3, #2]
|   28:   e5d32003        ldrb    r2, [r3, #3]
|   2c:   e5c31003        strb    r1, [r3, #3]
| [...]
|
| Doesn't quite have the peculiar "byte order" of your example,
| though.

Ah there is a much bigger story there, __packed__ allows the struct
pointer to be at an unaligned address by forcing compiler to operate on
it bytewise.  Scroll down about halfway through this:

http://warmcat.com/_wp/2007/05/25/the-alignment-monster/

- -Andy

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