[ECOS] RE: memory alignment issue when compile eCos with codesourcery toolchain arm-none-eabi-gcc

["Chris Zimman" <czimman at bloomberg dot com>]

> We are using Freescale i.Mx31 which is an ARM11 chip.
> The problem happens when a 2-byte aligned address is assigned to
> pointer which requires 4-byte aligned. For example, in lan92xx_send()
> in if_lan92xx.c, one code line is as below,
> ----------
>        unsigned int data, *pdata;
>        pdata = (unsigned int *)sg_list[i].buf;
> -----------
> Here sg_list[i].buf is 2-byte aligned while pdata needs 4-byte aligned.
> Then following code will hang the system
> ----------
>        data = *pdata;
> ---------
> In fconfig.c, the problem is similar. Val_ptr is of "void *" type and
> it is pointed to a char in a long string (for command processing). It
> is not guaranteed to be 4-byte aligned. Then when setting IP address,
> following code will fail
> ----------
>         lp += diag_sprintf(lp, "%s", inet_ntoa((in_addr_t *)val_ptr));
> ---------
> Because (in_addr_t *) in function inet_ntoa expects val_ptr to be 4-
> byte aligned.
> 
> Do you think there is a way to work around this issue without code
> modification?

Hi Karl,

The ARM11 requires 32 bit accesses to be word aligned unless you have CP15 c1
set to allow unaligned access.  I am suspicious that this is what may be
happening based off of what you're saying.

See chapter 4 of
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0211j/DDI0211J_arm1136_r1
p5_trm.pdf

--Chris