Self Modifing Code was RE: Harvard vs. vonNeuman

I used to use a lot more self-modifying code in my early days then I do now, you could save precious bytes of memory by storing data values into the immediate operand of instuctions which used them --- I recall a "turning point" when one day I spent a fair bit of time debugging a problem which was related to two level deep self-modifying code - ie: Modified an instruction so that it would subsequently modify another instruction differently - I started to believe some of the nay-sayers about the evils of SM code after that :-) Case where I've *HAD* to use SM code: 8080 general purpose monitor - no way to read/write arbitrary I/O ports - have implemented it both as directly SM code in RAM based monitor, and as a "built" subroutine in RAM for ROM based monitor. Same for 8051 (except you have to overlay CODE and DATA address spaces obviously - this is fairly normal for a debugging environment). Cheers, Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Vintage computing equipment collector. http://www.parse.com/~ddunfield/museum/index.html