Re: [debian-sparc] Re: 2.6.0-test6
On Fri, 3 Oct 2003, Paul wrote:
> >All of the creator3D support I wrote is 32-bit and takes full advantage
> > of the UPA bandwidth. 64-bits or not makes no difference wrt. to this,
> > so your ignorance is showing again... The bus bandwidth of UPA
> > is 64-bytes in one transfer, not 64-bits. The 64-bit transfers are
> > accomplished using the UltraSPARC block load and store instructions
> > that move 64-bytes at a time in and out of the floating point registers.
> > These instructions are fully available in 32-bit mode.
>
> Again, you seem to be looking at it sheerly through the software side of
> things. The bus bandwidth is not 64 bytes. Bandwidth is a term of velocity:
> amount over time.
> http://dictionary.reference.com/search?q=bandwidth
> "2. The amount of data that can be passed along a communications channel in
> a given period of time. "
>
> So, Bandwidth would have to include the clock speed of the bus AND the data
> width. Which happens to be 64 bits.
>
> http://docs.sun.com/db/doc/805-7764-12/6j7a77hhh?a=view#z400010a55fa
> "The UPA 64-bit data bus provides the connection between the CPU module and
> the UPA graphics. The 64-bit UPA data shares the data bus with memory
> through six transceiver chips."
According to this document
(http://www.eecis.udel.edu/nsfri/docs/Ultra-II/UPA.pdf), the UPA *address*
bus is 64 bit wide, and its *data* bus is 144 bit wide, with 128 bits for
data and 16 bits for error checking.
I saw mentions of 64-byte transfer blocks in other documents, for example
for the prefetch instruction. Thanks Google for those interesting
documents. ;)
> Maybe I'm just an old fogey who remembers the days when you tried to wring
> out the performance by aligning software as closely to hardware as possible.
> Maybe I think it's strange/inelegant to have a nonworking architecture in
> the kernel source.
What are you talking about? nonworking architecture?
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