[net.micro.amiga] Blitter speed

OC.TREI@CU20B.COLUMBIA.EDU (03/27/86)

From: Peter G. Trei <OC.TREI@CU20B.COLUMBIA.EDU>



	While waiting for my official Commodore doc kit to arrive, I
borrowed a friend's hardware manual and started reading about the
blitter. It seems like a wonderful chip, and I conceived an
application which makes EXTREMELY heavy use of it. Which leads to my
question:

     Just how fast is the blitter? How many clock cycles per processed
word? How do the number of inputs, the presence of an output, and the
use of modulos and/or barrel shifts effect the speed? I cant find
anything to pin this down in the Hardware manual with any accuracy. My
estimates range from 7 million words/sec (This is the clock speed.
After all, this is a pipelined device) to a mere 62,500 words/sec (in
line with a claim that it can lay down lines at 'over 1 M pixels/sec').

    I guess I'll find out when I write the program, but I really think
this sort of nitty-gritty stuff should be in the hardware manual. If
it is in one of the volumes I have not obtained yet, I would
appreciate a pointer. If it is not in the docs, I hope CBN will post
the data here and put it in the next edition. I'd really like to pin down
the speed with better accuracy than a >100x range.

'Inquiring minds want to know!'

							Peter Trei
							oc.trei@cu20b
-------

dale@amiga.UUCP (Dale Luck) (04/01/86)

In article <1651@caip.RUTGERS.EDU> OC.TREI@CU20B.COLUMBIA.EDU writes:
>
>     Just how fast is the blitter? How many clock cycles per processed
>word? How do the number of inputs, the presence of an output, and the
>use of modulos and/or barrel shifts effect the speed?

The actual measured speed of the blitter depends on how heavy the memory
buss is already being used. Assuming no bitplanes/sprites/copper the blitter
has nearly 100% access to the buss. With 100% access the blitter can
read/write without any delay.  The it can move data from one point to
another is about 1.8M(words)/second. modulos do not affect timing.
barrel shifting will drop the max bandwidth to 1.3M(words/sec). Each
transfer is read and a write to the memory.  These estimates are
based on a single source and a single destination.
Dale Luck

horizontal lines can be drawn at a max rate of 28Mpixels/sec (b/w).

ekijak@ARDC.ARPA (04/12/86)

From: "Edmund S. Kijak" (POINT) <ekijak@ARDC.ARPA>


What does a blitter do?    What is a barrel shift?   Why would modulos (modulo
arithmetic ?) be of concern in graphics?