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A simple assembler for cpu used in course VLSI system design

Usage:

  • Clone the repo.
git clone https://github.com/fennecJ/VLSI-Assembler
  • Build
cd VLSI-Assembler/assembler
make
  • Run
./asm $(ASM_FILE_PATH) $(MACHINE_CODE_SAVE_PATH)

And the converted machine code will appeared in $(MACHINE_CODE_SAVE_PATH).

  • Add other instruction
    Go to file assembler/ins.c, you'll see something like:
char *op_table[] = {
    "NOP" , "BRA",
    "LD"  , "STR",
    "ADD" , "MUL",
    "CMP" , "SHF",
    "ROT" , "HLT",
    "EXT1", 
};

Then you can add any instruction on your favor depends on opCode of your instruction. Op's Opcode is set according to their index in the op_table.
For example, if you add an instruction DIV whose opCode is 9 (Insert between ROT and HLT), Then the modified op_table will be:

char *op_table[] = {
    "NOP" , "BRA",
    "LD"  , "STR",
    "ADD" , "MUL",
    "CMP" , "SHF",
    "ROT" , "DIV",
    "HLT", "EXT1", 
};

Note that the golden file in tst/ will be incorrect after this step, because the index of HLT become 10 (op_table[10] == HLT) and opCode of HLT is no longer 9 but 10, so the new generated opCode would be 1010 for HLT. You also need to modified RTL/cpu.v for new instruct, otherwise it won't work properly.

  • Clean built targets
make clean

Test with RTL code:

Set $(MACHINE_CODE_SAVE_PATH) to be ../RTL/sisc.prog and run the assembler. Use cmd

cd ASM/
./asm $(ASM_FILE_PATH) ../RTL/sisc.prog
cd ../RTL/
iverilog cpu.v -o cpu
./cpu

To see how RTL cpu run with machineCode sisc.prog.

  • Disclaimer: I do not own the right of cpu.v, if the owner hope me to remove the src code of cpu.v, please contact me. Please note that the license is only valid for file under dir assembler/

Known issues/bugs:

  • Only support one line comment token "//"
    Multi line comment token "/**/" is illegal and won't be implemented currently.

  • Comment must be seperated from code by at least 1 space
    e.g.

    (X) BRA END, CCZ// If cond is zero then goto end
(O) BRA END, CCZ // If cond is zero then goto end
                ^ There must be at least 1 space

  • Label must be added with a colon followed by beginning of instruction without space. e.g.

    (x)L1: NOP (invalid, space between colon and Q2)
(x)L1 :NOP (invalid, space between colon and L1)
(O)L1:NOP

  • opCode = 0 is reserved for NOP
    If you want to change opCode of NOP to other number, goto assembler/assembler.c, find funct set_all_field, and change

    if(i == 0)     //NOP
return ins;

    to

    if(i == NUM_OF_NOP)     //NOP
return ins;

  • Currently you can only add new instruct with format {inst dest, src}
    The instuct added to file assembler/ins.c must be with format {inst dest, src}, inst without dest and/or src is not allowed
    e.g.

    (X)JEQ R0        (Invalid, missing dest and/or src) 
(O)DIV R0, R1

    If you want to add instruct other than format {inst dest, src}, you need to modify funct set_all_field in assembler/assembler.c by yourself.

  • This assembler parser has no syntax checking function, user should make sure the input has no syntax error by their own.

  • The hex format is only acceptable way to assign value using label currently, and the leading zero cannot be omitted. The length of hex val must be exactly 8.
    e.g. If you want to assign 7:

    (X) Num1:7          (invalid, leading zero cannot be omitted)  
(O) Num1:00000007   (correct, leading zero is kept and length of hex val is exactly 8)

assembler default rule and example:

cc: cond code.
SHF and ROT: Right:positive/Left:negative.
The detail definition and implementataion of ins can be found in assembler/ins.c and RTL/cpu.v.