[U-Boot] A question in lowlevel_init.S

[Albert ARIBAUD]

Hi Vamsi,

Le 22/01/2011 05:18, krrish53 a écrit :
>
> Hello everybody,
> I have a question pertaining to almost every lowlevel_init.S. The code goes
> like
>
> /*make r0 relative the current location so that it*/
> /*reads SMRDATA out of flash rather than memory*/
> ldr r0,=SMRDATA
> ldr r1,_TEXT_BASE
> sub r10,r0,r1
>
> I couldn't relate the code to comments made ahead of that(how does TEXT_BASE
> - addrof(SMRDATA) yield the location of SMRDATA in flash. I totally dint get
> it.  Please enlighten me. I  greatly appreciate any response.

It would be easier if you gave the precise source code origin, filename 
and location of the code you're mentioning. I took the u-boot-arm 
current master branch, and could not exactly find any occurrence of "sub 
r10, r0, r1" so I looked for an appraoching sequence, and found e.g. 
arch/arm/cpu/arm926ejs/at91/lowlevel_init.S, line 63. Is this what you 
meant?

	/* memory control configuration */
	/* this isn't very elegant, but	 what the heck */
	ldr	r0, =SMRDATA
	ldr	r1, _MTEXT_BASE
	sub	r0, r0, r1
	add	r2, r0, #80

If so, the code does not compute TEXT_BASE - SMRDATA, rather the reverse 
: SMRDATA - TEXT_BASE, .i.e. the relative address of SMRDATA with 
respect to the image start (depending on START_FROM_MEM, in Flash or 
physical RAM). I assume #80 is an absolute base address of the actual 
SMRDATA, but I'm no at91 specialist.

> Thanks,
> Vamsi

Amicalement,
-- 
Albert.