add, addi, lw, sw, li, la, syscall, move, jal, jr, bgt, j.
Assume that: all registers are addressed by $register-name (like $s1; see your textbook
for range of valid register names and numbers); the end of program is recognized by the
end instruction, the program is loaded into memory at location 0; each label has 1 to 4.
characters; there is 1 or more space between the symbols in the program.
The input to your assembler is a text file consists of 1 to 50 assembly instructions. The
last instruction is .end. You can write your assembler in any language as long as we are
able to test it in the department.
The output of your program is a text file that contains the object code. The object code is
represented in hex format.
Your assembler should consist of two passes.
During the first pass, the assembler generates a table that correlates all user-defined
address symbols with their decimal equivalent value. The binary translation is done
during the second pass. The content of PC (Program Counter) stores the value of the
memory location assigned to the instruction or operand presently being processed. The
assembler sets this counter to 0 initially. A line of symbolic code is analyzed to determine
if it has a label (by the presence of a colon). If the line of code contains a label, it is
stored in the address symbol table together with its decimal equivalent number specified
by the content of PC. PC is then incremented by 4 and a new line of code is processed.
Instructions are translated during the second pass by means of table-lookup or other
procedures. There are three tables:
1. Pseudoinstruction table.
2. Instruction table.
3. Address symbol table.
The entries of the pseudoinstruction table are for pseudoinstructions such as li and move.
Each entry refers the assembler to a subroutine that processes the pseudoinstruction when encountered in the program. The instruction table contains the symbols for the rest of
instructions and their related information.
PC is initially set to 0. Lines of code are then analyzed one at a time. Labels are neglected
during the second pass, so the assembler goes immediately to the instruction field and
proceeds to check the first symbol encountered. It first checks the pseudoinstruction
table. A match with an entry sends the assembler to the corresponding subroutine. If the
symbol encountered is not a pseudoinstruction, the assembler refers to the instruction
table. If a match occurs, the instruction is converted to its equivalent machine code by the
use of address symbol table (if needed). The implementations of tables 1 and 2 are
optional. You must use a hash function for the implementation of Table 3.
NEED FOR HELPING !!
Edited 5 Years Ago by hzcsdtc: n/a