From: Baltissen, R (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2003-08-19 09:56:44
Hallo Nick, > The SCPU actually assumes mirror-ALL as its default .... So if I understand you correctly, the SCPU starts up in a mode where reading is done at full speed from its own memory and writing is done at 1 MHz to both the systems. The speedgain lays in the fact that normally there are more reads then writes to be done. (horrible translation IMHO) More speed can be gained by windowing the RAM-area running the risk that graphics disapear or never show. The advantage of the 64'er project was that it worked without the need for windows. Slowdown for some windows is still needed but some native C64 signals can tell a circuit when or when not to activate this slow-down. No external programming needed! The disadvantage was that the CPU was only used for plm. 50%. With a 14 Mhz 65816 one could run the system on 15 MHz which would end up with a C64 running on 8 MHz ALL-THE-TIME !!! The critical timing of this design was mentioned but that was a point in 1994 (or was it 1992) but not nowadays IMHO. The only thing that worries me is the fact that the VIC still can claim the bus for quite some ns. after the positive edge of CLK2. This means that in case of 8, we only can use 7 cycles. Keeping things more simple would mean using the systems own DOTCLOCK which provides us with 8 MHz and ending up with a 4 MHz C64. Disadvantage: only works with a 8 MHz 65xxx which doesn't exist thus forcing one to use a 14 Mhz 65816 which means waisting CPU-power. Remark for Oliver: when using the 65816, what about using its 16 MB capabilities? Can provide you with quite some nice ideas. -- ___ / __|__ / / |_/ Groetjes, Ruud \ \__|_\ \___| http://Ruud.C64.org =====DISCLAIMER================================================================= De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken. Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij overgebrachte virussen. The information contained in this e-mail is confidential and may be privileged. It may be read, copied and used only by the intended recipient. If you have received it in error, please contact the sender immediately by return e-mail; please delete in this case the e-mail and do not disclose its contents to any person. We don't accept liability for any errors, omissions, delays of receipt or viruses in the contents of this message which arise as a result of e-mail transmission. Message was sent through the cbm-hackers mailing list
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