HACK Machine Language & Assembler

Question 1

what is machine language

Answer 1

an agreed upon formalism, designed to code low-level programs as a series of machine instructions

Question 2

use of machine language

Answer 2

• define the interface between programming & logic gates
• define low level operations:
  
  • manipulating memory
  • basic logic operations

Question 3

what is opcode

Answer 3

corresponds to operations defined in the decoder circuitry

Question 4

what are the HACK machine registers

Question 5

what is the HACK machine computer

Answer 5

is a theoretical, simplified computer architecture designed for educational purposes
- von neumann
- 16-bit registers

Question 6

what does the D register store

Answer 6

data

Question 7

what does the A register store

Answer 7

data or address

Question 8

what does M stand for

Answer 8

implicit label which refers to the value of memory location pointed to by A
- RAM[A]

Question 9

what register do jump instructuions use

Answer 9

A

Question 10

how to load an immediate value into A

Answer 10

@value

Question 11

what is D;JGT condition

Answer 11

D > 0

Question 12

what is D;JGE condition

Answer 12

D >= 0

Question 13

what is D;JLT condition

Answer 13

D < 0

Question 14

what is D;JLE condition

Answer 14

D <= 0

Question 15

what is D;JEQ condition

Answer 15

D = 0

Question 16

what is D;JNE condition

Answer 16

D != 0

Question 17

what is 0;JMPcondition

Answer 17

unconditional jump

Question 18

how to define a jump in HACK machine language

Answer 18

@label
condition

i.e
@positive
D;JGE

Question 19

command to load data in memory into the data register

Answer 19

@value
D=M

Question 20

command to store data in data register into memory

Answer 20

M = D

Question 21

binary syntax of a C-instruction

Answer 21

111accccccdddjjj
- first 1 = C-instruction opcode
- second & third 1s = not used
- acccccc = comp bits
- ddd = dest bits
- jjj = jump bits

Question 22

binary syntax of A value

Answer 22

0vvvvvvvvvvvvvvvv
- 0 = A-instruction op-code
- vvvvvvvvvvvvvvv - 15-bit binary representation of the constant, therefore <= 32767

Question 23

HACK assembler translation steps

Answer 23

1. symbols
2. non-instructions
3. instructions

Question 24

types of symbols

Answer 24

1. predefined
2. labels
3. variables

Question 25

symbolic syntax of A instructions

Answer 25

@xxx

Question 26

symbolic syntax of C instructions

Answer 26

dest = comp;jump

Question 27

what are predefined symbols

Answer 27

- R0 - SCREEN - KBD - SP - LCL - ARG - THIS - THAT

Question 28

how are predefined symbols assembled

Answer 28

@SYM - replace SYM with its value

Question 29

what are labels

Answer 29

- LOOP - STOP

Question 30

how are labels assembled

Answer 30

- (SYM) - add to the table row - SYM|label's line number - @SYM - replace SYM with its value

Question 31

what are variable symbols

Answer 31

examples: i, sum

Question 32

how are variable synmbols assembled

Answer 32

- @SYM - first occurence: bind SYM to unsused value starting from 16 ELSE replace SYM with its value

Question 33

3 steps in assembling overview

Answer 33

1. initialisation 2. first pass 3. second pass

Question 34

what happens in the initialisation stage

Answer 34

1. open the source file 2. construct sumbol table (ST) 3. add default to ST

Question 35

what happens in the first pass

Answer 35

1. count lines 2. add labels to ST

Question 36

what happens in the second pass

Answer 36

1. add variables to ST 2. parse instructions 3. translate instructions 4. write binary code to output file