[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Joakim Tjernlund]

My board has a problem with this change. I added it manually to my tree 
and
now it wont boot at all(only with BDI2000 connected).
It seems like my board uses the warm start vector at all times.
Padding with 4 nop's after the _start symbol fixes the problem.
It might be due to a somewhat peculiar reset design but I cannot 
understand
why. Does this work for everyone else using 83xx?


 Jocke 

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Peter Tyser]

On Tue, 2010-10-19 at 12:07 +0200, Joakim Tjernlund wrote:
> My board has a problem with this change. I added it manually to my tree 
> and
> now it wont boot at all(only with BDI2000 connected).

Just to clarify, it won't boot with or without the BDI2000 connected,
correct?

> It seems like my board uses the warm start vector at all times.
> Padding with 4 nop's after the _start symbol fixes the problem.
> It might be due to a somewhat peculiar reset design but I cannot 
> understand
> why. Does this work for everyone else using 83xx?

Odd...  I don't have an 83xx board to test on unfortunately.  Nothing
jumps out as being obviously wrong in the assembly:

===== Pre-commit (works):
fe000100 <_start>:
fe000100:       3a a0 00 01     li      r21,1
fe000104:       60 00 00 00     nop
fe000108:       48 00 00 10     b       fe000118 <boot_cold>
fe00010c:       00 00 00 00     .long 0x0

fe000110 <_start_warm>:
fe000110:       3a a0 00 02     li      r21,2
fe000114:       48 00 00 0c     b       fe000120 <boot_warm>

fe000118 <boot_cold>:
fe000118:       3c 80 ff 40     lis     r4,-192
fe00011c:       60 00 00 00     nop

fe000120 <boot_warm>:
fe000120:       7c a0 00 a6     mfmsr   r5
fe000124:       48 00 00 05     bl      fe000128 <boot_warm+0x8>
fe000128:       7c e8 02 a6     mflr    r7

===== Post-commit (doesn't work):
fe000100 <_start>:
fe000100:       3c 80 ff 40     lis     r4,-192
fe000104:       60 00 00 00     nop
fe000108:       7c a0 00 a6     mfmsr   r5
fe00010c:       48 00 00 05     bl      fe000110 <_start+0x10>
fe000110:       7c e8 02 a6     mflr    r7

It'll be interesting to hear if the change affects other boards in the
same way.

Best,
Peter

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Joakim Tjernlund]

Peter Tyser <ptyser@xes-inc.com> wrote on 2010/10/19 17:51:11:
> 
> On Tue, 2010-10-19 at 12:07 +0200, Joakim Tjernlund wrote:
> > My board has a problem with this change. I added it manually to my 
tree 
> > and
> > now it wont boot at all(only with BDI2000 connected).
> 
> Just to clarify, it won't boot with or without the BDI2000 connected,
> correct?

It will only boot WITH the BDI2000. That is because my BDI sets
the PC before execute.

> 
> > It seems like my board uses the warm start vector at all times.
> > Padding with 4 nop's after the _start symbol fixes the problem.
> > It might be due to a somewhat peculiar reset design but I cannot 
> > understand
> > why. Does this work for everyone else using 83xx?
> 
> Odd...  I don't have an 83xx board to test on unfortunately.  Nothing
> jumps out as being obviously wrong in the assembly:

The difference is that I suspect execution starts at 0xXXXXXX110 rather
than 0xXXXXXX100. BTW, I have my reset vector at 0x0

What causes a warm reset?

 Jocke

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Peter Tyser]

> > > It seems like my board uses the warm start vector at all times.
> > > Padding with 4 nop's after the _start symbol fixes the problem.
> > > It might be due to a somewhat peculiar reset design but I cannot 
> > > understand
> > > why. Does this work for everyone else using 83xx?
> > 
> > Odd...  I don't have an 83xx board to test on unfortunately.  Nothing
> > jumps out as being obviously wrong in the assembly:
> 
> The difference is that I suspect execution starts at 0xXXXXXX110 rather
> than 0xXXXXXX100. BTW, I have my reset vector at 0x0
> 
> What causes a warm reset?

My understanding is that a warm reset on the 8xxx CPUs isn't really a
hardware reset - its just when code explicitly jumps to the warm reset
entry point.  For example, this board used to jump to _start_warm when
"reset" was ran in U-Boot: 
http://git.denx.de/?p=u-boot.git;a=commitdiff;h=3792d7436e2bf881b6abdede5a481a62b5dedd55

During normal use I thought that the reset entry point was always
0xXXXXX100 and a warm reset would never occur.

What is the power on reset process like on your board?

Best,
Peter

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Joakim Tjernlund]

Peter Tyser <ptyser@xes-inc.com> wrote on 2010/10/19 20:39:41:
> 
> > > > It seems like my board uses the warm start vector at all times.
> > > > Padding with 4 nop's after the _start symbol fixes the problem.
> > > > It might be due to a somewhat peculiar reset design but I cannot 
> > > > understand
> > > > why. Does this work for everyone else using 83xx?
> > > 
> > > Odd...  I don't have an 83xx board to test on unfortunately. Nothing
> > > jumps out as being obviously wrong in the assembly:
> > 
> > The difference is that I suspect execution starts at 0xXXXXXX110 
rather
> > than 0xXXXXXX100. BTW, I have my reset vector at 0x0
> > 
> > What causes a warm reset?
> 
> My understanding is that a warm reset on the 8xxx CPUs isn't really a
> hardware reset - its just when code explicitly jumps to the warm reset
> entry point.  For example, this board used to jump to _start_warm when
> "reset" was ran in U-Boot: 
> 
http://git.denx.de/?p=u-boot.git;a=commitdiff;h=3792d7436e2bf881b6abdede5a481a62b5dedd55

> 
> During normal use I thought that the reset entry point was always
> 0xXXXXX100 and a warm reset would never occur.

I am not so sure about this. Perhaps the Freescale guys can set us 
straight?

> 
> What is the power on reset process like on your board?

A bit fuzzy ATM, will have to look at that.

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Wolfgang Denk]

Dear Joakim Tjernlund,

In message <OFBC383CCF.86B567D6-ONC12577C1.006A80D5-C12577C1.006AA773@transmode.se> you wrote:
>
> > During normal use I thought that the reset entry point was always
> > 0xXXXXX100 and a warm reset would never occur.
> 
> I am not so sure about this. Perhaps the Freescale guys can set us 
> straight?

Originally U-Boot (well, PPCBoot, to be more precise) had this notion
of a "warm start", but I quickly learned that this makes little sense
in a boot loader. When we execute the "reset" command,. we usually
want to _really_ reset the system into operational mode, including
not only the CPU itself but also co-processors (which might be running
some form of microcode or DMA), external controllers (to stop them
from doing DMA or other data transfers), NOR flash (to make sure it is
in read mode so we can execute code from it), etc.

Whenever this was not possible (usually due to hardware design
"features") this almost always was experienced as a "bug in U-Boot"
because there were situations where the board could only be reset
through full power cycle.

My recommendation is: stop thinking of "warm boot"; either perform a
"reset" (and that be a real, hard reset of the CPU core and all
peripherals), or just continue to run ;-)

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Wenn Du ein' weise Antwort verlangst, Mu?t Du vern?nftig fragen.
                                                -- Goethe, Invektiven

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Joakim Tjernlund]

Wolfgang Denk <wd@denx.de> wrote on 2010/10/19 22:04:17:
> 
> Dear Joakim Tjernlund,
> 
> In message <OFBC383CCF.86B567D6-ONC12577C1.006A80D5-C12577C1.
> 006AA773 at transmode.se> you wrote:
> >
> > > During normal use I thought that the reset entry point was always
> > > 0xXXXXX100 and a warm reset would never occur.
> > 
> > I am not so sure about this. Perhaps the Freescale guys can set us 
> > straight?
> 
> Originally U-Boot (well, PPCBoot, to be more precise) had this notion
> of a "warm start", but I quickly learned that this makes little sense
> in a boot loader. When we execute the "reset" command,. we usually
> want to _really_ reset the system into operational mode, including
> not only the CPU itself but also co-processors (which might be running
> some form of microcode or DMA), external controllers (to stop them
> from doing DMA or other data transfers), NOR flash (to make sure it is
> in read mode so we can execute code from it), etc.
> 
> Whenever this was not possible (usually due to hardware design
> "features") this almost always was experienced as a "bug in U-Boot"
> because there were situations where the board could only be reset
> through full power cycle.
> 
> My recommendation is: stop thinking of "warm boot"; either perform a
> "reset" (and that be a real, hard reset of the CPU core and all
> peripherals), or just continue to run ;-)

We do. Even have a HRESET button and it still doesn't work.
There is one thing though: At address 0x100(and 0x110) we have a
branch to where the boot is really located. This is because
we have small sectors in the beginning of the flash and we want to
use those as environment etc.

 Jocke

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Wolfgang Denk]

Dear Joakim Tjernlund,

In message <OF7EBFC833.2F0E9C3D-ONC12577C1.00737E7A-C12577C1.0073EC18@transmode.se> you wrote:
>
> There is one thing though: At address 0x100(and 0x110) we have a
> branch to where the boot is really located. This is because
> we have small sectors in the beginning of the flash and we want to
> use those as environment etc.

Why don't you use the rest of this sector for code? All you need to do
is adapt the linker script a bit...

Without that - where is your exception handler code? This is supposed
to be there, too...

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
The management question ... is not _whether_ to build a pilot  system
and  throw  it away. You _will_ do that. The only question is whether
to plan in advance to build a throwaway, or to promise to deliver the
throwaway to customers.       - Fred Brooks, "The Mythical Man Month"

[U-Boot] commit "powerpc: Remove warm reset entry point" does not work on mpc83xx

[Joakim Tjernlund]

Wolfgang Denk <wd@denx.de> wrote on 2010/10/19 23:13:59:
> 
> Dear Joakim Tjernlund,
> 
> In message <OF7EBFC833.2F0E9C3D-ONC12577C1.00737E7A-C12577C1.
> 0073EC18 at transmode.se> you wrote:
> >
> > There is one thing though: At address 0x100(and 0x110) we have a
> > branch to where the boot is really located. This is because
> > we have small sectors in the beginning of the flash and we want to
> > use those as environment etc.
> 
> Why don't you use the rest of this sector for code? All you need to do
> is adapt the linker script a bit...
> 
> Without that - where is your exception handler code? This is supposed
> to be there, too...

ah, this is only during the early steps. The flash gets mapped to
0xf0000000 and RAM is mapped to 0x0