Re: PowerBasic rocks!

On Sun, 17 May 2009 03:51:45 +0100, Nobody <nobody@xxxxxxxxxxx> wrote:

On Sat, 16 May 2009 16:34:27 -0700, bill.sloman wrote:

Pre-fetching doesn't seem to make sense in this context. The example
was just read, add and store.

Modern DRAMs are essentially wide-word block-transfer devices, and
modern caches are very smart. The inner "add" loop is a few (five,
actually) pipeline-locked instructions working on blocks of input and
output values located in data cache. Really smart programmers doing
really time-critical stuff - like video games - take cache
architecture into account when planning their code.

None of this gets around the fact that if you are looking at 128M
words of data, the memory is outside the cache, on the other side of a
word-wide bus.

When you're reading and writing cache lines using burst transfers, there's
no need for the bus width to match the word size. The Pentium and up use a
64-bit memory bus; many graphics cards use a 256-bit memory bus.

Memory access time is the bottle-neck here, and the fastest solution
has to be three blocks of memory - one for the new data and two for
the accumulated data (which you ping-pong between up-date cycles) with
three separate paths to a DSP processor that can add fast enough to
match the memory transfer rate.

Sure; a wider bus or multiple buses will transfer data faster. It doesn't
actually matter whether you have 1x 16-bit bus + 2x 32-bit buses or a
single 80-bit bus. Except that a single 80-bit bus would be more
flexible.


Hey, this seems to be a little faster...


' down-count experiment...

X = 63999999
ZOT:
S(X) = S(X) + A(X)
DECR X
IF X <> 0 THEN GOTO ZOT


Presumably it eliminates an immediate compare.

John

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