Electronic – If I am writing a processor in VHDL, how can I get an assembler to ease testing

assemblermicroprocessorvhdl

Provided that I have written a simple microprocessor design in VHDL where I have decided what instructions it has to do each task, I will then have to write test code in machine language which is tedious and error prone.

A simple assembler would be like a “lite text processor” where it can convert assembly instructions to machine code by parsing text of the assembly language program. Each assembly instruction is a mnemonic and the parser will also figure our how to fit the parameters into the generated machine instruction word e.g register name, variable name e.t.c

Is there an easy solution to developer an assembler of such a nature?

Best Answer

Puh, writing an assembler would actually imply writing a parser, and then writing some kind of Abstract syntax Tree-to-instructions converter.

I think this would, if you want to do it most simple, be done by defining a grammar (ie a set of instructions and registers and immediate value formats and how to combine them) and then generating a parser for that. You can go the Bison/Yacc/flex way about that, but I hear good things about ANTLR, so I'd give that a try.

In the medium run, you'd probably want to implement a clang or GCC backend. That would have the "nice" side effect that you could then compile e.g. C to your instruction set.

Related Solutions

Electronic – in dsPIC33 assembler, can I use all of the w registers

The C30 compiler expects a subroutine to preserve W8-W15 but it may trash W0-W7. You therefore only need to save/restore W8-W14 if you are going to use them. Otherwise if you can make do with W0-W7 for scratch, then there is no need to save/restore anything.

Note that you never explicitly push/pop W15 since that's the stack pointer. The way to save/restore it is to pop the same amount of stuff off the stack that you push onto it, including the subroutine return address which is generally popped by executing RETURN.

I set the C30 mode to not use stack frames. Stack frames can occasionally be a aid in debugging, but otherwise they are just a waste of space and cycles. There is a command line option to the C30 compiler which prevents it from using stack frames, and therefore doesn't emit the silly link/unlink sequences. I have so far always used that and not had problems.

One other issue with your code above is that you forgot to declare _FunctionName global.

Electronic – Writing a VHDL Module

I'm pretty sure you accidentally clicked "Verilog Module" instead of "VHDL Module":

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The code generated should look something like this:

   COMPONENT mymodule
   PORT(
      clk    : IN std_logic_vector(3 downto 0);
      enable : IN std_logic_vector(3 downto 0);   
      output : OUT std_logic_vector(3 downto 0)
   );
   END COMPONENT;

Delete the accidental Verilog Module and try again paying close attention to which Source Type you choose.

Best Answer

Related Solutions

Electronic – in dsPIC33 assembler, can I use all of the w registers

Electronic – Writing a VHDL Module

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