Wednesday, August 06, 2008

Almost there!

I've now got things almost working, single stepping is rock solid and I now have the RTS instruction being simulated fine. There appears to be a slight glitch where on a specific instruction in XeO3 it doesn't step properly but jumps off to $FFFF for some reason - no idea why as yet. While I'm trying to figure this out I'll start adding breakpoints to the interface and then get the symbol table loaded.

I suddenly realised that I shouldn't be passing the an interface top the symbol table to the CPU model, but an interface to an expression evaluation module. This means the CPU code could evaluate expressions if it needs to, and that leaves me to deal with symbol table lookups inside the expression evaluation without having to worry about it. You'll still be able to write your own symbol table so that you can load funny symbol file formats, and you'll still be able to query for symbols but this time it'll go through the evaluation system instead.

I'll pinch the expression stuff from SNasm and put an interface around it, this means it'll handle anything SNasm could (which was a lot!). It also means that watches (with their complex expressions) should be a breeze to process, all I need to do is add the new [..] context to get memory from the target. Should be fun when its all working! I'm still not sure how fast its all gonna run, as getting lots of memory over a parallel cable isn't quick, still emulators should be very fast and at least you'll be using a common interface then!

I also realised that each module (ICPU, ISymbolTable and IComms) needs to be able to change some options, so I'll add a new interface that means it can pop up an options box and allow you to change things. For example, the CPU module might allow you to enable undocumented opcodes which aren't on by default.

So there you go! Its going pretty well so far! Once I get it to a basic level, I'll need to see if I can get some other coders to try it out and give me some feedback. of course, having only SNasm labels might hinder things a little, but then again it would be a good opportunity to have someone else write a module and tell me how easy or hard it was!


Anonymous said...


Would it be possible to remote debug via RR-net instead of serial port?


Mike said...

See my response on the main blog page :)