aliu@nunki.usc.edu (Alejandro Liu) (12/13/88)
Hi UseNet Users:
I have been reading some of the specs about the C-128, because a
program I am writing, and I need some information. First I heard
that the 128's MMU can handle 1 Meg of memory, has that thing has been
realeased? Second, How do you use the MMU to do Bank Switching? I
know there is a register at location $FF00, but what does each bit
means? I know that there is a Kernal subroutine that calculates the
value, but I don't like the 15 Bank system they have a Commodore.
What are the exact additions to the Kernal Jump table? I only know
the old jumping points, but I know that they have added quite a few
subroutines, I would like to know what are them and where are they.
(Just the jump table) And last but not least, How do you make the MMU
do virtual memory for pages 0 and 1. I know that this is possible.
--
aliu@nunki.usc.edu (Alejandro Liu)
(Simple .signature, $CHEAP$) Geoffrey.Welsh@isishq.FIDONET.ORG (Geoffrey Welsh) (12/14/88)
> From: aliu@nunki.usc.edu (Alejandro Liu) > Message-ID: <2140@nunki.usc.edu> > I have been reading some of the specs about the C-128, > because a > program I am writing, and I need some information. First > I heard > that the 128's MMU can handle 1 Meg of memory, has that > thing has been > realeased? Second, How do you use the MMU to do Bank Switching? To answer your first question: No. The MMU was designed to handle up to four 64K banks for a total of 256K. The problem is that there aren't enough pins on the MMU chip to handle the extra lines, so Commodore never connected them. As a result, you'd have to take the MMU out of its casing and re-wire the MMU to a larger carrier in order to take advantage of that ability. This is not a job even for the most skilled hacker! To answer your second question: get the C128 Programmer's Reference Guide from Bantam and/or 128 Internals from Abacus. Explaining the MMU to someone who has no idea what's going on is damned difficult, if not impossible. The C128 PRG also provides memory maps for C64 and C128 modes with Kernal jump tables and info on how to use those routines plus specs and info on most of the peripheral chips in the 128. > And last but not least, How do you > make the MMU > do virtual memory for pages 0 and 1. I know that this > is possible. You've got to be kidding! Virtual memory on a C128? The closest thing you'll get is the ability to relocate pages zero and one (i.e. z-page and the stack). True virtual memory would require that hardware exceptions occurr when certain address ranges are used. I suppose the REU would provide a good place to swap memory blocks to & from (certainly disk drives are out of the question!), but the question would then be "what use is that to existing applications?"... none. -- Geoffrey Welsh - via FidoNet node 1:221/162 UUCP: ...!watmath!isishq!Geoffrey.Welsh Internet: Geoffrey.Welsh@isishq.FIDONET.ORG
daveh@cbmvax.UUCP (Dave Haynie) (12/15/88)
in article <2140@nunki.usc.edu>, aliu@nunki.usc.edu (Alejandro Liu) says: > Keywords: C-128, MMU, virtual memory, memory map > Hi UseNet Users: > I have been reading some of the specs about the C-128, because a > program I am writing, and I need some information. Sounds to me like you need a C128 Programmer's Reference Manual. > First I heard that the 128's MMU can handle 1 Meg of memory, Nope. The current MMU is limited to 128K of RAM, plus the ROM. In theory, the MMU design would permit an MMU to be built that would support 1 meg of RAM, though in practice, only 256K of RAM would be possible without some software problems (the banking method _changes_ when you go over 256k). > Second, How do you use the MMU to do Bank Switching? I know there is a > register at location $FF00, but what does each bit means? The MMU register map looks something like this: Location Register $D500 Configuration Register $D501 Preconfiguration Register A $D502 Preconfiguration Register B $D503 Preconfiguration Register C $D504 Preconfiguration Register D $D505 Mode Configuration Register $D506 RAM Configuration Register $D507 Page 0 Pointer LOW $D508 Page 0 Pointer HIGH $D509 Page 1 Pointer LOW $D50A Page 1 Pointer HIGH $D50B MMU Version Register $FF00 Configuration Register (same as $D500) $FF01 Load Configuration Register A $FF02 Load Configuration Register B $FF03 Load Configuration Register C $FF04 Load Configuration Register D The configuration and preconfiguration registers have the same format: Bit 7: Unused (for 256K banking in a new MMU) Bit 6: Select RAM bank 0 or 1 Bit 5,4: ROM HI Space (00 = System ROM, 11 = RAM) Bit 3,2 ROM MID Space (00 = System ROM, 11 = RAM) Bit 1: ROM LOW Space ( 0 = System ROM, 1 = RAM) Bit 0: I/O Space (0 = System I/O, 1 = HIGH ROM Space) If you write to the CR, the banking takes place immediately. If you write to a PCR, nothing immediately happens. If you write to an LCR (doesn't matter what you write), the contents of the corresponding PCR get transferred to the CR and the banking gets set. This allows several common setups to be stored and used without having to have I/O space turned on or having to disturb a register. The RAM Configuration register looks like this: Bit 7: Unused (for 256K banking in a new MMU) Bit 6: Select bank 0 or 1 for the VIC chip Bit 5,4: For expansion banking beyond 256K in a new MMU Bit 3: Sharing banks at top of RAM (0 = Not Shared, 1 = Shared) Bit 2: Sharing banks at bottom of RAM (0 = Not Shared, 1 = Shared) Bit 1,0: Amount shared (00 = 1K, 01 = 4K, 10 = 8K, 11 = 16K) The page registers specify the actual location of the 8502's page 0 and 1. Bit 0 of each HIGH register specifys the bank, while the LOW register specifys the page in that bank. You should write first to the high register, then to the low, for each pair. > I know that there is a Kernal subroutine that calculates the > value, but I don't like the 15 Bank system they have a Commodore. > What are the exact additions to the Kernal Jump table? I only know > the old jumping points, but I know that they have added quite a few > subroutines, I would like to know what are them and where are they. I don't know how the software works, maybe Fred will say something about it. You should really get the C128 Programmer's Reference Manual, which tell all about this stuff. And I'm not just saying that 'cause I helped write it :-) > aliu@nunki.usc.edu (Alejandro Liu) > (Simple .signature, $CHEAP$) -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy Amiga -- It's not just a job, it's an obsession