Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ames!ucbcad!ucbvax!CORY.BERKELEY.EDU!dillon From: dillon@CORY.BERKELEY.EDU (Matt Dillon) Newsgroups: comp.sys.amiga Subject: Re: Help: definitions and terminology Message-ID: <8704201929.AA26502@cory.Berkeley.EDU> Date: Mon, 20-Apr-87 14:29:49 EST Article-I.D.: cory.8704201929.AA26502 Posted: Mon Apr 20 14:29:49 1987 Date-Received: Tue, 21-Apr-87 03:05:25 EST Sender: daemon@ucbvax.BERKELEY.EDU Lines: 101 -> From: Matthew Dillon -> -> To do all the stuff the Copper does in the 68000 would take ->considerably more time (10%+). -From: hah@isum.intel.com (Hans Hansen) - -Anybody want to guess at maybe 100-200%. Lets consider what is done by -the copper, (Agnus), and also understand that the copper is the heart of I was talking about the Copper instructions. -the three chip co-processor call the "Custom chips". When you consider that -these three chips handle all of the serial IO thru the RS-232 port, the Serial I/O is not DMA. -> ->>chipmem -> -> Chipmem refers to the area of memory that the custom chips can access ->with their DMA. Currently, the custom chips have only enough address lines to ->access the lower 512K of memory. Any custom chips which steal processor ->cycles only do so when the processor is attempting to access this area of ->memory. - -Close but Chipmem actually refers to the first 2MegBytes of RAM in the -Amiga's memory map. The existing copper, due to a lack of pins, can only -address 512k of memory. Can you read? I said 'Currently'. ->>fastmem -> -> FastMem refers to any expansion memory you might add to your ->Amiga beyond the first 256K expansion you stick in the front of your machine. ->That is, any RAM beyond the 512K mark is fast memory. - -Close again but.. Fast mem refers to the memory above the chip mem area -of the memory map, or any RAM at or above 0x00200000. Obviously the person who asked the questions in the first place is not a vetren in programming the Amiga. There was no need to go into such detail. -> -> The term 'fastmem' comes from the fact that the 68000 can run at ->full speed when referencing FAST mem no matter how many cycles the custom ->chips are stealing from CHIP memory. - -Two problems here. First the custom chips don't "steal" memory cycles, -instead they utilize the bandwidth more effecently than the 68k and are -therefore told to take more of the chip memory bandwidth to get the -job done. (I know it's splitting hairs but how can you steal something -that you are ordered to take?). Secondly the reason the 68k can run -faster when not addressing chip mem is that the chip mem area is seperated -from the rest of the 68ks address map thru a DMA port that fully isolates -the custom chips and their RAM from the rest of the system. Only by -addressing the chip RAM area of the Amiga's memory map and then thru -an arbitration process within two PALs is the 68k allowed access to the -chip mem area. Look guy, just because I don't go into detail doesn't mean my answer is incomplete. 0 problems. -> ->>graphmem -> -> Graphics memory? Generic term meaning the memory available to ->some graphics device. On the Amiga, this is the lower 512K portion of memory. - -I believe this is a non-Amiga term to describe the assigned video RAM -area of their systems. I SAID THAT. -PArtially correct, the 68k's bandwidth is 7.14MByte however the bandwidth -of the Amiga is really 14.28MBytes. The custom chips run at twice the -data rate of the 68k! This is the main reason that the 68020 turbo, 14.28MHz -processors work so well, (well maybe just a little help from the forsight -of Dale Luck and C-A). A 7.14Mhz 68000 has a memory bandwidth of 3.57MBytes/sec. (Every 16bit fetch takes 4 clocks). I was under the impression that CHIP memory had a bandwidth double the 68000's, which would be 7.14MBytes/sec. Am I wrong? can anybody at C-A help? - For the most part Matt's answers are correct, and I would not -have added to his answer except I was just tired of seeing people say -that the custom chips steal memory cycles! The DMA circuit in the -Amiga is very efficient and using the copper to do tasks is the most -efficient use of the chip memorys bandwidth. The fact that the 68k - For the most part, Hans answers to my answers to the original question were uncalled for. Although he did correct some mistakes I made (the clock rate for the 68020 board, the AM29000), most of his qualms made no sense at all, and simply reiterated what I said. Rightly, his message should have been in response to the original question, not my answer to the original question. -Matt