Memory struggle

I have really struggled to do ROM to RAM mapping on the C64 and Atari 8-bit. The processes is very much alike, between the two systems. The problem is making the process consistent. Additionally, re-running the same program with the same memory calls causes crashes. I have in the time being just made 1.1 versions very simple. I wanted to use the same graphics that I made for the TI-99/4A. In theory that is possible. I just have not been able to consistently do so.

My compromise:

Instead of using this code:

100 MEMTOP=PEEK(106) 

110 GRTOP=MEMTOP-4 

120 POKE 106,GRTOP

140 GRAPHICS 0 

160 CHROM=PEEK(756)*256 

170 CHRAM=GRTOP*256 

500 FOR N=0 TO 1023 

510 POKE CHRAM+N,PEEK(CHROM+N) 

520 NEXT N 

540 POKE 756,GRTOP