Assumptions:

1. Macro is defined at the top of the file before the code where macro is used

2. Clear accumulator resets the accumulator. No address is present in the accumulator

3. Label table is used instead of symbol table as variables are not given, here symbol table will only have labels

4. Execution stops after the end statement. The code written after the end statement is not executed.

5. The maximum memory size= 12 bits

6. Operands:

1. For add,mul,lac,dsp and sub operand should be a defined address or a constant (cannot be an undefined address)

2. For brn , brz, brp should have a defined valid label

3. sac,inp should have a defined or undefined address (not a constant)

4. div should have first as defined address or constant, second and third can be defined or undefined address but not a constant

7. The number of parameters supplied to macro = number of parameters supplied during call

8. Label name cannot be an opcode name and cannot have a Macro name anywhere in it. For example if ADDTWO is a macro, then: "SUB","ADD","ADDTWOXYZ" are invalid Labels.

9. Comments ca be added with the help of ; or /

Design:

1. Data table contains all the addresses defined in the main code

2. Macro table contains the macro definition and the labels, parameters and instructions used in it

-- do we need this? 3. Opcode table is a list containing all the opcodes encountered in the main program stored in order

4. When a macro call is encountered, the instructions present in the macro table for the respective macro definition is substituted in the main instruction table

5. Explain the structure of the tables used

6. All the commands are converted to upper case, to avoid case errors.

Errors handled in first pass:

1. Multiple macro definitions

2. Invalid Label name (Label cannot have a macro name in it and it cannot be an opcode name)

3. Multiple label definitions

4. Address supplied should be of integer type.

5. Address supplied should be lesser than 12 bits=4096.

6. Incorrect number of parameters supplied in a macro

7. Incorrect number of parameters supplied for an opcode

8. END of program not found

9. MEND/ENDM for macro not found

10. Invalid opcode name/Macro name

Pseudocode for first pass:

declare END found variable

while instruction is available and END is not encountered:

if instruction empty line

skip line

if end

break

is instruction a comment

if yes remove comments

is instruction macro definition

put macro definition in dictionary

while mend is not encountered

add the instruction to macro table/dictionary

nextline

if mend is not encountered at all then throw error

what is the length of the instruction

does instruction[0] have a label of the form li:

if label is not previously defined:

if yes put it in the label label

else throw multiple definition error

in this case instruction[1] is opcode remaining is operand

else instruction[0] is opcode, remaining is operand

how many operands does the instruction have

which opcode does the instruction have

is the opcode a valid opcode

does the num of operands match the required number of operands for your opcode

if both yes put it in opcode table

append instruction in the table

else if is it a call to a macro

if yes put the parameters in a list

go to macro table and iterate over its instructions

substitute fields with given parameters

append substituted instruction in instruction Table

put the opcode in the opcode table

put label in label table

handle errors

if no throw incorrect number of operands error

Instruction add on every error