[U-Boot] A question in lowlevel_init.S

[U-Boot] A question in lowlevel_init.S

[krrish53]

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.

Thanks,
Vamsi
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[U-Boot] A question in lowlevel_init.S

[Albert ARIBAUD]

Hi Vamsi,

Le 22/01/2011 05:18, krrish53 a ?crit :
>
> 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.

[U-Boot] A question in lowlevel_init.S

[Reinhard Meyer]

Dear Albert ARIBAUD,
> Hi Vamsi,
>
> Le 22/01/2011 05:18, krrish53 a ?crit :
>>
>> 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.

I am not aware of any AT91SAM9xxx systems right now that uses low-level init, it
would only make sense for those that boot directly from NOR, without
AT91BOOTSTRAP involved.
Since we also have no NAND_SPL for AT91, it might well be that only AT91RM9200
systems use low level init code...

To clarify, AT91BOOTSTRAP is the first code loaded by the SoC ROM into internal
SRAM and therefore restricted in size to only 4k for some AT91 SoCs. This code
has to init the SDRAM and load u-boot into SDRAM (hence the relocation stuff
was not really needed for AT91).

Best Regards,
Reinhard

Best Regards,
Reinhard

[U-Boot] A question in lowlevel_init.S

[Eric Bénard]

Hi,

On 22/01/2011 08:39, Reinhard Meyer wrote:
> I am not aware of any AT91SAM9xxx systems right now that uses low-level init, it
> would only make sense for those that boot directly from NOR, without
> AT91BOOTSTRAP involved.

cpu9260 (at91sam9260 / 9g20 based) is using low-level init as it boots from 
NOR and is not using at91bootstrap.

Eric

[U-Boot] A question in lowlevel_init.S

[Reinhard Meyer]

Dear Eric B?nard wrote:
> Hi,
>
> On 22/01/2011 08:39, Reinhard Meyer wrote:
>> I am not aware of any
ADD: working
>> AT91SAM9xxx systems right now that uses low-level init, it
>> would only make sense for those that boot directly from NOR, without
>> AT91BOOTSTRAP involved.
>
> cpu9260 (at91sam9260 / 9g20 based) is using low-level init as it boots from
> NOR and is not using at91bootstrap.

Those CPUs are broken since relocation was introduced. It would be nice to see
them demonstrated working out of NOR with low level init enabled...

Best Regards,
Reinhard

[U-Boot] A question in lowlevel_init.S

[krrish53]

Sorry for not mentioning the file name. its here
uboot/arch/arm/cpu/arm920t/at91rm9200/lowlevel_init.S and also in
uboot/board/samsung/smdk2410/lowlevel_init.S 
Thanks for all your responses so far people.


Reinhard Meyer wrote:
> 
> Dear Eric B?nard wrote:
>> Hi,
>>
>> On 22/01/2011 08:39, Reinhard Meyer wrote:
>>> I am not aware of any
> ADD: working
>>> AT91SAM9xxx systems right now that uses low-level init, it
>>> would only make sense for those that boot directly from NOR, without
>>> AT91BOOTSTRAP involved.
>>
>> cpu9260 (at91sam9260 / 9g20 based) is using low-level init as it boots
>> from
>> NOR and is not using at91bootstrap.
> 
> Those CPUs are broken since relocation was introduced. It would be nice to
> see
> them demonstrated working out of NOR with low level init enabled...
> 
> Best Regards,
> Reinhard
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> http://lists.denx.de/mailman/listinfo/u-boot
> 
> 

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[U-Boot] A question in lowlevel_init.S

[Ulf Samuelsson]

2011-01-22 11:19, Reinhard Meyer skrev:
> Dear Eric B?nard wrote:
>> Hi,
>>
>> On 22/01/2011 08:39, Reinhard Meyer wrote:
>>> I am not aware of any
> ADD: working
>>> AT91SAM9xxx systems right now that uses low-level init, it
>>> would only make sense for those that boot directly from NOR, without
>>> AT91BOOTSTRAP involved.
>> cpu9260 (at91sam9260 / 9g20 based) is using low-level init as it boots from
>> NOR and is not using at91bootstrap.
> Those CPUs are broken since relocation was introduced. It would be nice to see
> them demonstrated working out of NOR with low level init enabled...

I do not think the term "NOR" flash is correct.
"NOR" refers to the technology used in the memory cell,
and both "SPI Flash" and "Dataflash" are "NOR" flashes.
A better term is "parallel flash".

Atmel obsoleted all "parallel" flash during 2010, so
don't expect any boards to contain "parallel" flash
to come out in the future.

Looks like boards.cfg does not even contain most at91 boards
for some reason, so MAKEALL does not even try to build them
Think that should be fixed.

> Best Regards,
> Reinhard
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> http://lists.denx.de/mailman/listinfo/u-boot


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Best Regards
Ulf Samuelsson

[U-Boot] A question in lowlevel_init.S

[krrish53]

Hi Albert,

Thanks for your response. 
Albert ARIBAUD wrote:
> 
> Hi Vamsi,
> Thanks for your response. Sorry for not mentioning the file name. its here
> uboot/arch/arm/cpu/arm920t/at91rm9200/lowlevel_init.S and also in
> uboot/board/samsung/smdk2410/lowlevel_init.S. My doubt is that as of now
> no relocation happened and the code is still being executed from flash
> rite, why would TEXT_BASE required in fetching the values from flash. This
> really confuses me. 
> 
> Let me tell my understanding about. When the system starts u-boot.bin
> resides in the flash and starts executing start.S(by figuring out the
> entry point from u-boot.lds). And from u-boot.lds, the text section starts
> at 0x0000000 and other sections follow it. I really dont understand here
> the necessity of considering TEXT_BASE for writing SMRDATA values into
> registers as there is no RAM in the picture yet. This is the I would
> greatly appreciate a little detailed response.
> 
>  Thanks very much. 
> 
> Le 22/01/2011 05:18, krrish53 a ?crit :
>>
>> 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.
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> http://lists.denx.de/mailman/listinfo/u-boot
> 
> 

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