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Moving Variable Data and Gaining Memory
Posted: Sun Jun 12, 2016 5:45 pm
by GreyGhost
I had this idea pop into my head today and wanted to ask the experts. It seems possible to move variable storage out of free RAM and have it some place else. I was thinking @ $a000. If this could be done, then all of Basic memory would be just for code. This would take away the myth that $a000 can only be used by ML prgs or data storage. One question would be, would this work for string storage as well?
Code: Select all
poke45,1:poke46,160:clr:rem**start of variables**
This would take care of numeric but I notice that string storage is not at the same place in memory. String memory starts at the end of Basic memory and work its way up.
Code: Select all
poke51,0:poke52,192:clr:rem**string storage**
Does this sound like it would work? Any hardware reasons why it wouldn't? This idea could even be used with the cassette buffer on unexpanded machines.
Re: Moving Variable Data and Gaining Memory
Posted: Mon Jun 13, 2016 1:18 am
by Mike
You can gain an extra byte at the start by POKEing
POKE45,0:POKE46,160:CLR.
The top of string space in 51/52 is (re-)set from 55/56 if you do CLR, so it's better to do
POKE55,0:POKE56,192:CLR.
Of course, all four POKEs are necessary for this technique (i.e. a single CLR at the end of the 4-POKE-sequence suffices), which comes handy when the program leaves less than 8K for variables in the "standard" BASIC range up to $7FFF. And yes, this works. Only thing, when SAVEing BASIC would attempt to take the end of the program from the start of the variables, and that would save character ROM and I/O along, which you wouldn't want. You'd have to run some kind of OLD/RENEW routine before SAVE to correct 45/46.
In
MAXIGRAFIK, one option of the config. program was to put the entire BASIC workspace (including user program) into the range $A000..$BFFF. The
VFLI panning viewer/slideshow also puts the room for BASIC into BLK5. (SCNR
)
Cheers,
Michael
Re: Moving Variable Data and Gaining Memory
Posted: Mon Jun 13, 2016 4:24 pm
by malcontent
GreyGhost wrote:This idea could even be used with the cassette buffer on unexpanded machines.
I'm curious if this would work too.
Re: Moving Variable Data and Gaining Memory
Posted: Mon Jun 13, 2016 8:03 pm
by GreyGhost
malcontent wrote:GreyGhost wrote:This idea could even be used with the cassette buffer on unexpanded machines.
I'm curious if this would work too.
I may have been a little hasty saying that about string variables, not understanding that their memory location is actually set by the bottom of memory, but it absolutely works with numeric variables.
Run this short program in VICE and then check the cassette buffer with the monitor.
Code: Select all
10 poke45,60:poke46,3:clr
20 a=36879:b=36878:c=36877:d=36876
30 print a,b,c,d
I would think the best way to get some usefulness out of this would be to use a loader program. Define custom characters, declare constants and variables and dimension arrays then load the main program. Would issuing a run command reset these pointers as well? Has anyone tried issuing a 'goto10' command in the keyboard buffer instead of run after a load?(mind wondering again).