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SubjectRe: Strange macros set HZ value for timer channel zero
On Fri, 17 Aug 2001, george anzinger wrote:

> "Richard B. Johnson" wrote:
> >
> > To whomever maintains the timer code, greetings.
> >
> > When using Linux on the AMD SC520 chip, the system time will
> > not be correct because the PIT clock is 1.1882 MHz instead of
> > the usual 1.19318 MHz. Therefore, I put a conditional value
> > in ../linux/include/asm/timex.h .
> >
> > #ifndef _ASMi386_TIMEX_H
> > #define _ASMi386_TIMEX_H
> >
> > #include <linux/config.h>
> > #include <asm/msr.h>
> > #ifdef SC520
> > #define CLOCK_TICK_RATE 1188200 /* Underlying HZ */
> > #else
> > #define CLOCK_TICK_RATE 1193180 /* Underlying HZ */
> > #endif
> >
[SNIPPED...]

Okay. I still don't know what's wrong. The following code
shows that your MACRO does produce the right stuff:
Script started on Mon Aug 20 10:02:58 2001

# cat xxx.c
#include <stdio.h>
#include <sys/time.h>
#define __KERNEL__
#include <linux/timex.h>


int main()
{
printf("Divisor = %d\n", LATCH);
printf("%02x %02x\n", LATCH & 0xff, LATCH >> 8);
}

# gcc -o xxx xxx.c
In file included from /usr/local/include/linux/timex.h:54,
from xxx.c:4:
/usr/local/include/asm/param.h:21: warning: `CLOCKS_PER_SEC' redefined
/usr/local/include/timebits.h:44: warning: this is the location of the previous definition
# xxx
Divisor = 11932
9c 2e
# gcc -DSC520 -o xxx xxx.c
In file included from /usr/local/include/linux/timex.h:54,
from xxx.c:4:
/usr/local/include/asm/param.h:21: warning: `CLOCKS_PER_SEC' redefined
/usr/local/include/timebits.h:44: warning: this is the location of the previous definition
# xxx
Divisor = 11882
6a 2e
# exit
exit

Script done on Mon Aug 20 10:03:50 2001


Ignoring the "multiple-defined" warnings, one can see that the
divisor and the stuff that will be put into the registers is
correct. Sorry to bother you.

It looks like this problem has to be fixed with a hammer. For some
reason, the chip doesn't like the new values.

I'm off by about 7 seconds per minute:

Connected to platinum, wait...
platinum time was Mon Aug 20 10:10:10 2001
chaos time was Mon Aug 20 10:10:03 2001
Difference = 7 second(s)
platinum time was Mon Aug 20 10:10:11 2001
chaos time was Mon Aug 20 10:10:04 2001
Difference = 7 second(s)
platinum time was Mon Aug 20 10:10:11 2001
chaos time was Mon Aug 20 10:10:04 2001
Difference = 7 second(s)
platinum time was Mon Aug 20 10:10:12 2001
chaos time was Mon Aug 20 10:10:05 2001
Difference = 7 second(s)
platinum time was Mon Aug 20 10:10:12 2001
chaos time was Mon Aug 20 10:10:05 2001
Difference = 7 second(s)
platinum time was Mon Aug 20 10:10:13 2001
chaos time was Mon Aug 20 10:10:06 2001
Difference = 7 second(s)
platinum time was Mon Aug 20 10:10:13 2001
chaos time was Mon Aug 20 10:10:06 2001
Difference = 7 second(s)

Aborted by ^C

It gains time, meaning that the divisor is too small. Unfortunately,
I can't read what was written to the actual chip. I can only detect
its affect. 60 / 67 = 0.89 * 100 = 89. 1188200/89 = 13350 = 0x3426
as a divisor. It doesn't make sense because both LSB and MSB are
wrong. If one was wrong I could guess that the previous hadn't set
up properly and needs more delay.

Anyway. I will continue to search.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).

I was going to compile a list of innovations that could be
attributed to Microsoft. Once I realized that Ctrl-Alt-Del
was handled in the BIOS, I found that there aren't any.


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