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SubjectRe: AMD SC410 boot problems with recent kernels
On Fri, 21 Dec 2001, H. Peter Anvin wrote:
> > there are boot problems with new kernels on AMD SC410 processors.
>
> "On one particular SC410 board."

Ok, but it's one of the most widespread embedded x86 boards in Europe.

> The loop counter you're outputting is the 2nd byte of the loop counter,
> which really isn't interesting;

This was just from the last test: the result was %ch=0 and %cl=1.

> what probably makes more sense to output is the value of %dx in your
> code.

%dx? Do you mean %cx or do I not understand the code? ;)

> I would like to suggest making the following changes and try them out:
>
> a) Change A20_TEST_LOOPS to something like 32768 in the new kernel code.

Still reboots.

> b) Add a "call delay" between the movw and the cmpw in your old_loop
> and see if it suddenly breaks;

No, it still works.

> c) Check what your %dx value is (if it's nonzero, there might be an
> issue.)

I assume you mean in my old_wait code, at the lines where I give out the
stuff to the LED ports? Neither %dl nor %dh has something different from
0 here. How could something come into %dx here?

> d) Once again, please complain to your motherboard/BIOS vendor and tell
> them to implement int 15h, ax=2401h.

I'll do that, but this won't help for the hundrets of boards which are
still out there and worked fine with the previous code...

> e) Add a strictly serializing instruction sequence, such as:
>
> pushw %dx
> smsw %dx
> lmsw %dx
> popw %dx
>
> ... where the "call delay" call is in a20_test.

Hope I understand you correctly - I'm not an assembler wizzard yet ;) Is
this correct:

----------8<----------
a20_test:
pushw %cx
pushw %ax
xorw %cx, %cx
movw %cx, %fs # Low memory (segment 0x0000)
decw %cx
movw %cx, %gs # High memory area (segment 0xffff)
movw $A20_TEST_LOOPS, %cx
movw %fs:(A20_TEST_ADDR), %ax # put content of test address...
pushw %ax # ... on stack
a20_test_wait:
incw %ax
movw %ax, %fs:(A20_TEST_ADDR)

pushw %dx
smsw %dx

call delay # Serialize and make delay constant

lmsw %dx
popw %dx

cmpw %gs:(A20_TEST_ADDR+0x10), %ax
loope a20_test_wait

popw %fs:(A20_TEST_ADDR)
popw %ax
popw %cx
ret
---------->8----------

Still reboots with this code.

Robert
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| Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de |
| Pengutronix - Linux Solutions for Science and Industry |
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