On Saturday 18 February 2017, 12:01:05 Gerrit Heitsch <email@example.com> wrote: > On 02/18/2017 09:38 AM, firstname.lastname@example.org wrote: > > On Saturday 18 February 2017, 08:24:26 smf <email@example.com> wrote: > >> On 17/02/2017 20:26, Gerrit Heitsch wrote: > >>> That can be fixed by using a static RAM instead of DRAMs. > >> > >> It can be fixed by latching signals as well. > >> > >> My point is that a 100% VIC II in an FPGA would have the VSP problem, or > >> it's not 100%. AFAIK vice doesn't have the VSP problem either. > > > > actually x64sc can emulate it :) (its optional, "VSP Bug Emulation" in > > VICII settings) > > > > and no, the problem can _not_ be fixed (only) by using SRAM - that was > > tried and proven wrong long ago. its an urban myth that doesn't want to > > die :) > Well, the VSP-Problem happens because DRAMs use destructive readout, > meaning even a read cycle has to write the data back to the cells. This > happens inside the DRAM once /RAS goes high. This is not the case with > SRAM, a read cycle will just read the contens of a cell without > destroying them. So when you have a problem with address lines changing > while /RAS goes down and your latch latches the wrong address, you might > read the wrong data, but you CANNOT destroy the RAM contents this way as > you can with DRAM when you confuse the row decoder. > > I have done a SRAM replacement for the C64 using a 128KB SRAM, a > 74HCT573 and a 74HCT32 and so far no one was able to detect the VSP bug > when using it. as said, others have done it too and found that the VSP bug still exists - to remove it for certain you must add an additional circuit that prevents those writes to wrong addresses from happening. (but then, with such circuit, you dont need sram) -- http://www.hitmen-console.org http://magicdisk.untergrund.net http://www.pokefinder.org http://ar.pokefinder.org There is no such thing as a moral or an immoral book. Books are well written or badly written. <Oscar Wilde> Message was sent through the cbm-hackers mailing listReceived on 2017-02-18 12:02:07
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