[rescue] J90 on epay

[Joshua D. Boyd]

On Fri, Feb 28, 2003 at 03:23:02PM -0500, Dave McGuire wrote:

>    IOS stands for Input/Output System.  The J90 IOS is based on a VME64
> cardcage containing an IO}B interface (a high-speed channel directly to
> a CPU), a VME SS5 (which does RAID, caching, and error handling) and
> disk/network interfaces.  The VME SS5 sets up high-speed DMA
> transactions into the Cray processors' memory, which run over the IOBB
> bus.

First, aren't there more than 1 IOB and VME SS5s in the machine you
showed me down the street?

Second, does the SS5 just set up the DMA, or does the SS5 actually do
the DMA?  It seems to me that if the SS5 doesn't do the DMA, then either
the IO card (ethernet, scsi, hippi, whatever) needs to understand cray
memory, or else the cray memory needs to accept VME style DMA, where as
having the SS5 take DMA from the IO card, then stuff it into cray memory
by a second DMA transaction would be better for accomidating 3rd party
cards.  But, I don't really know.  Just inquiring further into the inner
workings of Cray IO.