7.11.Hack平台上的VM实现

\(7.11.\)VM Implementation on the Hack Platform

1.Program compilation and translation

• When we translate from Jack to VM, we lost the notion of constructors, methods, because everything becomes functions.
• When we translate from VM to assembly, we lost the notion of functions, because we just have a long stream of assembly commands.

2.VM convention

  In order to tranlate the VM code into assembly code, we need to comply to certain conventions:

1. VM programming convention: One file in any VM program is expected to be named Main.vm; one VM function in this file is expected to be named main.

2. VM implementation convention: When the VM implementation starts running, or is reset, it starts executing the argument-less OS function Sys.init.Sys.init then calls Main.main, and enters an infinite loop.

3. Hardware platform convention:

   • We request that the code you see here will be stored in the target computer's instruction memory beginning in address 0, for our Hack computer is programmed to start executing the program beginning with address 0.
   • So we first set SP = 256. By doing this, it will determined that the stack should begin in this address in the whole stream.
   • Then we call Sys.init.

SP = 256
Call Sys.init