[rescue] SS5 mobo

[Dave McGuire]

On Mar 2, 2004, at 4:04 PM, Janet L. Campbell wrote:
>>    I must be misremembering the internal architecture of the SS5 then,
>> and if that's the case, I stand corrected.  Does the operating system
>> not "see" an Mbus from its perspective on an SS5?  (I don't have one
>> handy at the moment)
>
> No, there's no Mbus visible at all.
>
> The microSparc and TurboSparc CPUs incorporate the IU, FPU, SRMMU, 
> first
> level cache, memory controller and Sbus controller all onto one chip.
> The TurboSparc also has a second level cache external to the chip.
> Nearly everything that attaches to the CPU hooks in through either the
> memory bus (RAM, the AFX slot) or the Sbus 
> (parallel/SCSI/ethernet/...).
>
> The SuperSparc and HyperSparc CPUs have the memory controller and Mbus 
> to
> Sbus interface on the mainboard, not on the CPU modules.  The Mbus was
> needed as an abstraction layer to allow multiple CPU transactions to be
> handled cleanly and to deal with cache coherence.

   I'm misremembering then, probably getting it mixed up with the 
SS10/SS20 architecture.  Thanks for the info.  It's been a while. :-)

> The microSparc/TurboSparc memory access latency is a lot lower because 
> the
> overhead of the Mbus glue isn't there.  Memory transactions also don't
> have to fight for bus space with Sbus transactions, so they can be 
> issued
> immediately.  This gave the SS4/SS5 the lowest memory latency of any
> pre-Ultra.

   Was this a latency/bandwidth tradeoff?

> -Janet [just another hardware hacker]

   You rock. :-)

       -Dave

--
Dave McGuire                      "My tummy hurts now, but my soul
Cape Coral, FL                   feels a little better."     -Ed