[U-Boot-Users] v2p4 porting troubles

[U-Boot-Users] v2p4 porting troubles

[Joshua Lamorie]

Gidday there,

We have a custom made board containing not much more than a Virtex-II Pro
(v2p4) and 16 Megs of Mobile SDRAM.  We are trying to port Linux, and in
preparing we've successfully built kernels and code for a development board
from Amirix.

But...

We have had a series of problems with getting u-boot to work.  Firstly, this
is a small Virtex-II, so we are unable to put everything into BRAM.  So
we've made a stripped down version of Amirix's ppcboot-lite, that is
supposed to load u-boot, which then will load Linux.

Ppcboot-lite runs fine out of BRAM.  However we've had several problems with
executing from SDRAM.  With various versions of the IPIF interface we have
gone through the various Machine Check Exceptions problems with jumps to
0x700 and 0x200.

Now, it seems that we have found a working configuration (ipif v1.0.d) that
lets us run code compiled by EDK (on WinXP under VMWare), but there is an
odd problem with the same code compiled by our Linux cross-compiler.

We have some LEDs connected to memory mapped I/O, and our test code writes
to it.  The EDK compiled binary makes the following assembly for the output
part.

stw     r0,0(r9)

This works fine, and the LEDs blink all pretty and flashy like.

The Linux tools compile...

stw     r9,0(r0)

However, the LEDs respond with blankity nothingness.  Using XMD, we swap
around these general purpose (according to how we read the docs) registers
(r8,r10, r1 etc.) , and sometimes it works and sometimes it doesn't.

In the mailing-list archive, I've seen mention of a common SDRAM problem
with u-boot, but it wasn't clear if this was just for Virtex-IIs or what.

Has anyone seen a problem like this?  Is it our toolchain?  Could it be
signal integrity on our board? (we have slowed things on the bus down to
16MHz, just in case)

We are using crosstools-0.26, with gcc-3.3-20040112 and glibc-2.3.2.

Questions for clarification are welcome.  Pointers, smack-up-side-the-heads,
hints, cajoles, rants are also welcome.

Joshua Lamorie
Department of Random Walks
Xiphos Technologies Inc.

[U-Boot-Users] v2p4 porting troubles

[Joshua Lamorie]

Gidday again,

    In further investigating this problem we have seen a pattern.  The
failure constantly occurs when the instruction is compiled as...

stw rX,0(r0)

    where X is 1-31.

    We see that instead of writing the data to the address pointed to by r0,
it writes the data to address 0x0 of physical memory (we have virtual memory
disabled).  When I look at the PowerPC Processor Reference Guide (pp.
80-82), it mentions that for the addressing modes Register-Indirect with
Immediate Index, Register-Indirect with Index, and Register Indirect, if rA
is set to 0 (refering also to r0) then an index of 0 is used instead of the
value of r0.

    So if this is the problem, why is our compiler making code that does
this?  I'm new to PPC assembler, so perhaps I'm interpreting this
incorrectly.

    Can you recommend a toolchain that would be better than the one we're
currently using? (listed below)

    Thanks in advance.

Joshua Lamorie
Director of Brownian Motion Control
Xiphos Technologies Inc.

----- Original Message ----- 
[snip]
> The Linux tools compile...
>
> stw     r9,0(r0)
>
> However, the LEDs respond with blankity nothingness.  Using XMD, we swap
> around these general purpose (according to how we read the docs) registers
> (r8,r10, r1 etc.) , and sometimes it works and sometimes it doesn't.

[snip]

> We are using crosstools-0.26, with gcc-3.3-20040112 and glibc-2.3.2

[U-Boot-Users] v2p4 porting troubles

[Wolfgang Denk]

In message <004101c40b6d$69274aa0$cb01a8c0@xiphos.ca> you wrote:
> 
>     So if this is the problem, why is our compiler making code that does
> this?  I'm new to PPC assembler, so perhaps I'm interpreting this

Maybe your compiler / assembler is brogen?

>     Can you recommend a toolchain that would be better than the one we're
> currently using? (listed below)

ELDK 3.0?

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
When the ax entered the forest, the trees said, "The handle is one of
us!"                                               -- Turkish proverb

[U-Boot-Users] v2p4 porting troubles

[Eric St-Jean]

(i'm working with the original poster, Joshua Lamorie)

On Tue, 16 Mar 2004, Wolfgang Denk wrote:

> In message <004101c40b6d$69274aa0$cb01a8c0@xiphos.ca> you wrote:
> >
> >     So if this is the problem, why is our compiler making code that does
> > this?  I'm new to PPC assembler, so perhaps I'm interpreting this
>
> Maybe your compiler / assembler is brogen?
>
> >     Can you recommend a toolchain that would be better than the one we're
> > currently using? (listed below)
>
> ELDK 3.0?
>

thank you for the suggestion!

i had missed the ELDK when i looked for a toolchain originally. I
downloaded the latest version, installed from binary:

ELDK version 3.0
ppc_4xx: Build 2004-02-16

and compiled my little test program, which basically just loops and
outputs values to a memory-mapped register that is plugged into LEDs.

to my amazement, the ELDK compiler made the same "mistake" (in quotes
because it's entirely possible that it's my limited ppc405 knowledge that
leads me to thinks it's a mistake):

00018304 <XIo_Out32>:
   18304:       94 21 ff e0     stwu    r1,-32(r1)
   18308:       93 e1 00 1c     stw     r31,28(r1)
   1830c:       7c 3f 0b 78     mr      r31,r1
   18310:       90 7f 00 08     stw     r3,8(r31)
   18314:       90 9f 00 0c     stw     r4,12(r31)
   18318:       3d 20 00 03     lis     r9,3
   1831c:       80 1f 00 0c     lwz     r0,12(r31)
   18320:       90 09 84 b0     stw     r0,-31568(r9)
   18324:       81 3f 00 0c     lwz     r9,12(r31)
   18328:       80 1f 00 08     lwz     r0,8(r31)
   1832c:       91 20 00 00     stw     r9,0(r0)
   18330:       7c 00 06 ac     eieio
   18334:       81 61 00 00     lwz     r11,0(r1)
   18338:       83 eb ff fc     lwz     r31,-4(r11)
   1833c:       7d 61 5b 78     mr      r1,r11
   18340:       4e 80 00 20     blr

(notice that this is the XIo_Out32() function generated by Xilinx XPS)

the problem is at 1832c. it correctly puts the absolute address in r0, and
the data to output in r9. it then tries to store r9's contents at [r0+0].

Looking at the PP405's UM, i see this in the stw instruction page:

=====================
An effective address (EA) is calculated by adding a displacement to a base
address, which are formed as follows:
* The displacement is formed by sign-extending the 16-bit d instruction
field to 32 bits.
* If the rA field is 0, the base address is 0.
* If the rA field is not 0, the contents of register rA are used as the
base address.

The contents of register rS are stored into the word referenced by EA.
=====================

so using r0 as a pointer won't work: the cpu won't use the contents of r0,
but will use 0. And we verified that: the value indeed gets output to 0
in memory.

Both ELDK's compiler and my other toolchain, a crosstool 0.26-generated
toolchain (powerpc-405-linux-gnu-gcc version 3.3.3 20040112 (prerelease))
generate this "flawed"  code.

Which would explain why our u-boot port isn't working, as presumably,
"mistaken" code is generated elsewhere as well.

This looks like a gcc problem, but perhaps someone on this list could
offer some guidance:
- do all powerpc's, not just the 405, have this behavior (of using 0
instead of r0 when the rA field is 0)?
- if so, why would these compilers generate code that seems flawed?
- if not, are we supposed to invoke the compiler in a particular way?

The compiler that is part of Xilinx EDK, powerpc-eabi-gcc gcc version
2.95.3-4 Xilinx EDK 6.2 Build EDK_Gm.1, does not produce this flaw (it
uses r9 as the address, r0 as the data), which correctly outputs to the
correct address.

i realize that at this level, it's not a u-boot problem and that this
mailing list is probably not the best avenue to ask for advice, but seeing
as some people here have ppc / xilinx experience, perhaps someone would
care to make a comment.

thank you!

-- 
______________________________
Eric St-Jean        esj at wwd.ca

[U-Boot-Users] v2p4 porting troubles

[Wolfgang Denk]

In message <Pine.LNX.4.58.0403161421230.24165@strange.wwd.ca> you wrote:
>
> to my amazement, the ELDK compiler made the same "mistake" (in quotes
> because it's entirely possible that it's my limited ppc405 knowledge that
> leads me to thinks it's a mistake):
...
> (notice that this is the XIo_Out32() function generated by Xilinx XPS)

Which sort of code does this tool generate? C code? Then it would  be
indeed  a compiler probile, and I definitely would like to see this C
code.

> Looking at the PP405's UM, i see this in the stw instruction page:

This behaviour is standard and well-known on PPC.

> This looks like a gcc problem, but perhaps someone on this list could

I don;t thinkthat GCC has such a serious problem.

> offer some guidance:
> - do all powerpc's, not just the 405, have this behavior (of using 0
> instead of r0 when the rA field is 0)?

Yes, this is standard on all PPC.

> - if so, why would these compilers generate code that seems flawed?

I don't think that a compiler would generate such code.

> - if not, are we supposed to invoke the compiler in a particular way?

Please show us the source code that produces such output; without all
discussion is in vain.


Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
Am I your nanny? The kernel is there to support  user  programs,  but
it's a _resource_ handler, not a baby feeder.     - Linus Torvalds in
      <Pine.LNX.3.91.960425074845.22041C-100000@linux.cs.Helsinki.FI>

[U-Boot-Users] v2p4 porting troubles

[Joshua Lamorie]

We're doing quite the tag team here.

> > (notice that this is the XIo_Out32() function generated by Xilinx XPS)
> Which sort of code does this tool generate? C code? Then it would  be
> indeed  a compiler probile, and I definitely would like to see this C
> code.

The code from Xilinx is as follows...

void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
{
   __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
(OutAddress));
}

... which is called from a simple program (found at the end of this email).

When this is compiled with the Xilinx toolchain (gcc 2.95 I think), it
generates the 'real' assembler as follows.

stw r0,0(r9)

However, when we put this into a linux toolchain (crosstools 0.26, or ELDK
3.0) it generates it with r0 and r9 in the opposite spots.

stw r9,0(r0)

We can change the C code to

   __asm__ volatile ("stw %1,0(%0); eieio" : : "r" (OutAddress), "r"
(Value));

Which seems to generate it correctly with the linux tools.

We have added this same function inside u-boot to toggle some LEDs as we are
debugging, but without changing anything it generates assembler that uses r4
and r3 and not r0 and r9, so there is no chance of a problem.

But why?  What is it about this C code which causes this sort of thing?
What constraints should be used? Where is decent, unambiguous documentation
of gcc inline assembler (instead of poorly explained examples)?

Thank you Wolfgang for your help so far.  Your comments have been very
useful.

Joshua

The original test code is as follows.

#define XPAR_IOBRIDGEV2P_PLB_0_BASEADDR 0x40000000
typedef unsigned long   Xuint32;    /**< unsigned 32-bit */
typedef Xuint32 XIo_Address;

void XIo_Out32(XIo_Address OutAddress, Xuint32 Value);
int simpletest();

int _start() {
        simpletest(0,0);
}

int simpletest()
{
        int i,j,k;

        XIo_Out32(XPAR_IOBRIDGEV2P_PLB_0_BASEADDR, 0x55);
        while (1) {
                for (i=1; i<30000; i++) {
                        for (j=i; j<5000; j*=2) {
                                for (k=0; k<1000; k+=5) {
                                }
                        }
                        XIo_Out32(XPAR_IOBRIDGEV2P_PLB_0_BASEADDR, i&0xFF);
                }
        }
        return(0);

}

void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
{

   //__asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
(OutAddress));
   __asm__ volatile ("stw %1,0(%0); eieio" : : "r" (OutAddress), "r"
(Value));
}

[U-Boot-Users] v2p4 porting troubles

[Wolfgang Denk]

In message <009b01c40baa$a324f2b0$cb01a8c0@xiphos.ca> you wrote:
> We're doing quite the tag team here.

;-)

> The code from Xilinx is as follows...
> 
> void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
> {
>    __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
> (OutAddress));
> }

This code is broken. The "r" operand specification sais  "a  register
operand  is  allowed  provided  that it is in a general register." Of
course R0 is a GPR as well. I think you need to use "m" (any kind  of
address that the machine supports in general) here:

     __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "m" (OutAddress));

> But why?  What is it about this C code which causes this sort of thing?

Actually this is no C code, but inline assembler. And yes, it is  the
code, which uses an inappropriate operand specification.

> What constraints should be used? Where is decent, unambiguous documentation

Use "m".

> of gcc inline assembler (instead of poorly explained examples)?

The GCC info pages are  pretty  useful.  See  File:  gcc.info,  Node:
Simple Constraints,

> Thank you Wolfgang for your help so far.  Your comments have been very
> useful.

I'm glad if I could help.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
Man did not weave the web of life; he  is  merely  a  strand  in  it.
Whatever he does to the web, he does to himself.     - Seattle [1854]

[U-Boot-Users] v2p4 porting troubles

[Joakim Tjernlund]

> In message <009b01c40baa$a324f2b0$cb01a8c0@xiphos.ca> you wrote:
> > We're doing quite the tag team here.
>
> ;-)
>
> > The code from Xilinx is as follows...
> >
> > void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
> > {
> >    __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
> > (OutAddress));
> > }
>
> This code is broken. The "r" operand specification sais  "a  register
> operand  is  allowed  provided  that it is in a general register." Of
> course R0 is a GPR as well. I think you need to use "m" (any kind  of
> address that the machine supports in general) here:
>
>      __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "m" (OutAddress));
>

If you want to avoid using R0, you should be able to use the "clobber" list.
like this:
__asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r" (OutAddress) : "r0" );

 Jocke

[U-Boot-Users] v2p4 porting troubles

[Joakim Tjernlund]

> > > The code from Xilinx is as follows...
> > >
> > > void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
> > > {
> > >    __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
> > > (OutAddress));
> > > }
> >
> > This code is broken. The "r" operand specification sais  "a  register
> > operand  is  allowed  provided  that it is in a general register." Of
> > course R0 is a GPR as well. I think you need to use "m" (any kind  of
> > address that the machine supports in general) here:
> >
> >      __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "m" (OutAddress));
> >
> 
> If you want to avoid using R0, you should be able to use the "clobber" list.
> like this:
> __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r" (OutAddress) : "r0" );
> 
>  Jocke

It appears that PPC has yet another register operand, "b".
"b" appears to mean all "r" registers but r0. The asm would then
become:
__asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "b" (OutAddress));

Anyone that knows more about the "b" operand?

[U-Boot-Users] v2p4 porting troubles

[Peter Ryser]

Joshua,

>The code from Xilinx is as follows...
>
>void XIo_Out32(XIo_Address OutAddress, Xuint32 Value)
>{
>   __asm__ volatile ("stw %0,0(%1); eieio" : : "r" (Value), "r"
>(OutAddress));
>}
>

Yes, this code is broken. You can use the work-around as pointed out by 
Wolfgang or you can use the xio.h that is part of u-boot and the Linux 
kernel.
In u-boot you can find it at board/xilinx/common/xio.h
In Linux you can find it at arch/ppc/platforms/xilinx_ocp/xio.h

I will make sure this piece of code gets fixed in EDK.

- Peter