teach me steppings & respins

[lau808]

what exactly is a stepping? b0 b2 b3 c0 ??? i understand which ones come first but what do they do from one stepping to the next? and is b3 to c0 better or more involved than a b2 to b3?

also what do they do in a respin?

i wont understand the most complex answer so layman terms would be nice, thanks for helping out a noob that wants to learn

 

[Elixer]

Stepping = bugfixes (usually).
Respin is another way of saying stepping (usually).
There could also be a respin in the design...

As in, we need a respin to get to stepping XYZ.

 

[veri745]

what exactly is a stepping? b0 b2 b3 c0 ??? i understand which ones come first but what do they do from one stepping to the next? and is b3 to c0 better or more involved than a b2 to b3?

also what do they do in a respin?

i wont understand the most complex answer so layman terms would be nice, thanks for helping out a noob that wants to learn

Minor revisions (i.e. B2 -> B3) generally only involve changes to the metal layers (re-routing signals, possibly minor logic fixes)

Major revisions (i.e. B2 -> C0) involve all new masks, including base layer masks. This means they can change fundamental behavior of transistors and can complete any layout changes necessary to fix whatever bugs or performance issues exist.

"Respin" just means that a new revision is created, whether major or minor.

 

[lau808]

thank u!

 

[pm]

Yeah, what the guys above said.

If it's a letter change, it means all layers are involved. If it's a number change, it means just metal has changed.

But mostly the significance of this has more to do with the engineers and the fabs involved than the end-users. Metal changes require less time in the mask shop to make the masks for the semiconductor machinery, and you can have material waiting in the fab that's halfway done (base layers are drawn) and metal-only steppings are cheaper (fewer new masks), so company's prefer to do metal-only steppings if they can.

You can't really know how much has changed by just relying on the letters or numbers. People will say - like Veri745 did - that all layer changes are big changes, but you can fundamentally change a whole lot with a metal only stepping. There are usually extra gates on a CPU specifically to be used to enable a metal-only stepping. At HP they used to be called "happy gates" because everyone would be happy with you if could fix an issue using them. I've also heard them called "bonus cells".... because your bonus will be higher if you can use them to fix a bug.

And steppings don't always include changes that end-users would care about. Some might be to improve manufacture yield. For example, I remember we did one stepping for a CPU to make the metal around metal 1 via's farther away to prevent a transcription error. Which in plain English means that the layers weren't lining up well in the fab and so we went in and spaced things out more. This had no impact on anything any customer would ever see... but helped us improve manufacturability of it.

Still, in the majority of cases what Veri745 and Elixer wrote is correct. Letters are big changes, and numbers smaller changes. Usually.


Patrick Mahoney
Intel Corp.
* Not an Intel spokesperson... just an engineer who hangs around on AT *

 

[lau808]

nice, ok another question...
when does the letters and numbers start over? with a refresh? (zambezi - vishera) or new arch? (phenom I - phenom II) (phenom II - bulldozer) and im not even sure how intels refreshes and archs work either.

 

[pm]

At Intel, we usually restart the letter process when we name a new project and "fork" (ie. copy) the database. So if you are working on a project named "Bob" and it's on it's C0 stepping and then some manager or architect dreams a new project which is Bob with twice the L2 cache and named it "Joe", we'd copy the database over and name the new database "Joe A0"

 

[lau808]

ok, so sb started new, and ivb will start new too right? unsure of all previous gens and what oreder they came in before hand as far as gulftown westmere nehalem etc et

 

[lau808]

lol bob to joe, thats awesome. thank u, so i can translate that as sb started over and so will ivb and haswell right?

 

[lau808]

oops, thought the other one didnt post, sorry

 

[veri745]

nice, ok another question...
when does the letters and numbers start over? with a refresh? (zambezi - vishera) or new arch? (phenom I - phenom II) (phenom II - bulldozer) and im not even sure how intels refreshes and archs work either.

AMD didn't seem to reset the major rev from Phenom I Agena (B2, B3) to Phenom II Deneb (C2, C3) or even for Phenom II Thuban (E0).

(http://www.cpu-world.com/info/AMD/K10_stepping_codes.html)

AMD FX is currently at B2, so they reset for that one.

 

[lau808]

oh wow, ok thanks. very helpful

 

[aigomorla]

lol bob to joe, thats awesome. thank u, so i can translate that as sb started over and so will ivb and haswell right?

you typically dont see A0's as retail.

And its each generation socket...

so example.. a 2#00 series will all be the same cpu with different cpuid values.
These will share the same stepping.

But once the cpu changes... like a 3#00 series it typically restarts at Joe A0.

 

[SickBeast]

A stepping more or less means when the CPU was manufactured, and it's usually a period of a few weeks or so.

A respin is a minor redesign of the CPU to fix problems like leakage, heat, or power consumption.

 

[pm]

lol bob to joe, thats awesome. thank u, so i can translate that as sb started over and so will ivb and haswell right?

Yeah, definitely. They all restarted on A0.