Hello Segher, * On Sat, Nov 25, 2017 at 04:15:52PM -0600 Segher Boessenkool wrote: > On Sat, Nov 25, 2017 at 10:03:49PM +0100, Spiro Trikaliotis wrote: [...] > > That is, if you have RAM at $0100-$01FF and you do not use that area for > > anything else, why should the CPU crash at all as long as you do not > > push more than 256 byte on it? [...] > See for example the 6530. It has 64 bytes of RAM and some I/O registers, > and only 10 address lines. The "simple" example in the MCS6500 hardware > manual has the RAM selected at xxxxxx0x11xxxxxx and the I/O at > xxxxxx1111xxxxxx. So, stack accesses to $01c0..$01ff go to RAM, but also > e.g. zero-page accesses to $00c0..$00ff go to the *same* RAM. That falls under the clause "if you have RAM at $0100-$01FF and you do not use that area for anything else, ..." ;) I was just curious to find out if the CPU might have a problem here, for example with a wrap-around while doing a JSR or an RTS, and the values being stored to/restored from $0100 and $01FF. There is nothing know about this, is it? > Long story short: older 6500 systems did not have a 256 byte stack, they > didn't even have 256 bytes RAM total :-) Now I've read that he was building on a replica 1. I looked here: http://www.brielcomputers.com/wordpress/?cat=17 The memchart (http://www.brielcomputers.com/wordpress/wp-content/uploads/2010/04/memchart.jpg) does not mention that $0100 - $01FF would not be RAM that is not reused. Thus, again, I do not see why there should be a problem here, especially if the code already worked on a SYM1. Regards, Spiro. -- Spiro R. Trikaliotis http://www.trikaliotis.net/ Message was sent through the cbm-hackers mailing listReceived on 2017-11-26 14:00:03
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