Possible to compile Jack to VM to ASM?

[gshubert17]

I'm working on chapter 11. When I'm finished, I will be able to compile Jack files to VM files. For now, the tools/JackCompiler does this. The resulting VM files execute fine in the VM Emulator.

The program I wrote for chapter 8 translates VM files to ASM files, which run fine in the CPU Emulator -- at least on the book's test files.

When I take a simple Jack file, compile it to a VM file with the JackCompiler, then run my chapter 8 VM translator on that VM file, I get an ASM file, but this last program crashes the CPU Emulator.

Is something like this possible? Or is it the case that the VM Emulator has different initializations than the CPU Emulator, and it is not intended to put these two tools end-to-end?

[cadet1620]

Yes, you should be able to compile Jack using your either the supplied compiler or your compiler, and use your VM translator to produce an ASM that will run on the CPUEmulator.

In addition to the .vm files generated by compiling the Jack sources, you also need to copy the n2t/tools/os/*.vm files into the directory before running your VM translator. Otherwise there will be calls to nonexistent functions. The calls will have an @targetFunction but since there is no corresponding (targetFunction) the assembler will assign a RAM address to targetFunction which will result in a jump to an unintended address and most likely a crash.

The other issue that you may run into is that your generated ASM may be larger than 32K. There are several things that you can do to reduce your generated code size. The two biggest VM commands are call and return. Notice that every return generates exactly the same ASM code. Your translator can write this code for the first occurrence of a return command, and for all other returns it just needs to jump to that code. You can do the same sort of thing for call, but it's a bit more complicated than just a jump since you need to pass the return address, number of arguments and target address to the common code.  

For more on VM translator optimization check these forum threads:
Generated code size
I HAVE DONE IT PEOPLE

--Mark

[gshubert17]

Thank you for all the information. I had noticed my ASM file contained 46,800 lines, and was too large to load. I had seen one of the optimization threads earlier, and now will study them in more detail.

I wonder whether I could remove some functions from my local copies of the *VM OS files before assembling the whole folder containing them and my Main function. It may be that there are too many calls from one module to another, that I can't remove any function without leaving a hole.

Again, thanks. You've helped me get unstuck here.

[cadet1620]

One of the optimizations talked about in the threads is having your VM emulator do a prescan of all the VM files that are to be translated and identifying uncalled functions so that they can be skipped when the ASM code is being generated.

When translating projects/11/Pong, my translator reports:

85 Functions, 18 unused.
Unused functions:
  Keyboard.readChar
  Keyboard.readInt
  Keyboard.readLine
  Math.max
  Math.min
  Math.sqrt
  Memory.poke
  Screen.drawCircle
  Screen.drawConditional
  Screen.drawHorizontal
  Screen.drawLine
  Screen.drawPixel
  Screen.drawSymetric
  String.dispose
  String.doubleQuote
  String.eraseLastChar
  String.intValue
  String.setCharAt

--Mark