[U-Boot] A question in lowlevel_init.S
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
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,
Dear 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.
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
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
Dear Eric Bénard 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
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 Bénard 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@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
2011-01-22 11:19, Reinhard Meyer skrev:
Dear Eric Bénard 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@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
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 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. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
participants (5)
-
Albert ARIBAUD -
Eric Bénard -
krrish53 -
Reinhard Meyer -
Ulf Samuelsson