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AuthorTopic: IBM Power PC 1GHz chip only runs properly at 933MHz  (Read 6289 times)

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Offline amigamad

IBM Power PC 1GHz chip only runs properly at 933MHz
« on: August 05, 2004, 05:35:00 PM »
A BUG IN THE 1GHz Power PC 750GX means that some instructions won't run at that clock frequency.And the work around is that instead people should run the 1GHz chip at 933MHz.


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Offline Elwood

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #1 on: August 05, 2004, 06:08:12 PM »
Those PC users should read the doc, a workaround is possible:

Use a code work-around involving the replacing of mcrf or logical CR instructions with code to move the CR to a general purpose register (GPR), perform the move or logical operation within the GPR, and then write the GPR back to the CR.
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Offline KennyR

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #2 on: August 05, 2004, 06:24:31 PM »
Even without any workaround, a performance loss of 67 MHz clock for a modern RISC processor is in the order of negligable at best and trivial at worst. And with the workaround, you don't even need to change the clock.

But you can bet it will feed many "PPC sucks!" rants from the x86 crowd. :) Myself, I'll probably wait until PPC gets a bug as huge and embarassing as the Pentium float bug before going there.
 

Offline minator

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #3 on: August 05, 2004, 07:38:28 PM »
Quote
But you can bet it will feed many "PPC sucks!" rants from the x86 crowd. :)


Probably, just point them to the errata pages for x86 chips.
Or tell them about the 3.6GHz P4, thermal throttling (clockspeed reduction) kicks in when it gets to hot, so much in fact that an older 3.4GHz will run faster.  It'll only run at full speed with water cooling!

You can also tell them about the recent Opteron bug (don't remember what exactly though).

So, nothing terribly exciting or unique.

What is surprising is the low number of bugs - only 8!
 

Offline Trev

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #4 on: August 05, 2004, 07:40:46 PM »
Yet another case of a product not working as advertised. . . . The bugs should be fixed, and the defective chips should be recalled and replaced. Period.
 

Offline Matt_H

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #5 on: August 05, 2004, 08:22:07 PM »
Whoops.

Though considering that this is the first I've heard of any PPC bug, and reports about flaws with Intel chips have been released consistently for years now, I think the PPC still has the better track record. Not to mention better power consumption and better instruction efficiency per cycle. ;-)
 

Offline Hammer

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #6 on: August 05, 2004, 11:21:15 PM »
@ Matt_H
Quote
Not to mention better power consumption and better instruction efficiency per cycle

Did you factor in the "Pentium M"?

Note with Pentium Classic's FPU bug i.e.
1. a workaround was issued (similar to Erratum 8's remedy). This was deemed to be unacceptable in market place due to nature of legacy software’s bias.  
2. replace the product with a new product.
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Offline Hammer

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #7 on: August 05, 2004, 11:34:26 PM »
Quote

Probably, just point them to the errata pages for x86 chips.

Note that, Intel has offered to replaced the flawed products i.e. for Pentium Classic(FPU bug) and early Pentium III 1.13Ghz(factory over-clocking).

I don’t recall AMD was guilty of early PentiumIII 1.13Ghz style factory overclocking for their Athlon chips. Their errata ussually involve with instruction bugs in certain batches e.g. Jpeg bug in certain early K7s batches*(pre-year 2000) and Opteron's REP MOVS** instruction(fixed with micro-code*** update)

*AMD has offered to replace them.
**Mainstream compliers don’t use these instruction combinations.
***Standard practise since P6 days.
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Offline Hammer

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #8 on: August 05, 2004, 11:38:27 PM »
Quote
You can also tell them about the recent Opteron bug (don't remember what exactly though).

Note that, down clocking K8s wouldn’t fix the REP MOVS instruction set issues. This micro-coding update also reveals differences between K7 and K8 core.

AMD has issued a micro-code update (via BIOS distribution) for REP MOVS instruction set. The issuing of micro-code updates was a standard practice since P6 days. After applying microcode update; the fix is transparent enough for every day usage (unlike IBM's remedy).  

"Such a combination was likely only to occur when people were creating code in assembler, and not when using compilers" paraphrase from AMD.
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Offline Hattig

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #9 on: August 06, 2004, 12:00:21 AM »
Quote
Note that, Intel has offered to replaced the flawed products i.e. for Pentium Classic(FPU bug) and early Pentium III 1.13Ghz(factory over-clocking).


Not the 1GHz Itanium that had to be run at 800MHz for a similar flaw.
 

Offline Hammer

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #10 on: August 06, 2004, 12:05:51 AM »
Quote
Not the 1GHz Itanium that had to be run at 800MHz for a similar flaw.

Note the 'Itanium 2 Processor Replacement' program (e.g. HP).

In Oz, it would be illegal to claim a product can do 1Ghz then say it can’t do 1Ghz and then offer 800Mhz workaround remedy. Breach of Trades Practise Act (TPA) Section 52 and 53.

PS; The new topic is about PPC not other processors.
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Offline Hammer

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #11 on: August 06, 2004, 01:03:48 AM »
Quote
Or tell them about the 3.6GHz P4, thermal throttling (clockspeed reduction) kicks in when it gets to hot, so much in fact that an older 3.4GHz will run faster. It'll only run at full speed with water cooling!

PIV on the desktop works fine at 3.6Ghz; but with appropriate ventilation (as dictated by Intel’s thermal requirements). There's no need for water cooling. Refer to Alienware's Area-51 Extreme PC as an example of doing it right.  

Some vendors don’t follow Intel’s guidelines, thus the activation of the safety feature.

Note that Intel’s early PentiumIII 1.13Ghz with PIV-EE’s level of cooling wouldn’t fix the problem.
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Offline bhoggett

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #12 on: August 06, 2004, 01:07:09 AM »
Irrespective of any x86 vs PPC argument, I'd regard any product like this to be faulty (not merely flawed) and unfit for distribution unless rebadged as a 933 MHz processor.
Bill Hoggett
 

Offline bhoggett

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #13 on: August 06, 2004, 01:12:45 AM »
Quote
Some vendors don’t follow Intel’s guidelines, thus the activation of safety feature.

Some vendors are complete morons. They go by the principle that if the CPU comes with a heatsink and fan, that should solve any overheating problems.

Of course, that's stupid. Air cooling depends on proper ventilation - which a lot of basic systems do not have - in the same way that a water cooler requires a radiator or some means of actually cooling the water itself.
Bill Hoggett
 

Offline Hammer

Re: IBM Power PC 1GHz chip only runs properly at 933MHz
« Reply #14 on: August 06, 2004, 01:38:37 AM »
Quote
Those PC users should read the doc, a workaround is possible:

Those mainstream PC users are only interested in product replacements and micro-code updates (transparent** after applying the BIOS updates).

Code substitution requires a code rewrite on all effected assembler code. How many assembler lines in a typical LinuxPPC distro (e.g. SUSE) again (rhetorical question)?

**Transparent to the existing software’s POV.
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