Chapter 7- Stack Arithmetic

Question 1

The vim language has what kind of data type?

Answer 1

It has one 16 bit data type that can be used as integer, Boolean or pointer.

Question 2

What are the formats of vm command?

Answer 2

There are 3 formats

1. Command (add)
2. Command ARG (goto loop)
3. Command arg1 arg2 ( push local 3)

Question 3

How many arithmetic commands are there?

Answer 3

Add, sub, neg, eq, gt, lt, and, or, not

Question 4

What are all the memory segments?

Answer 4

Argument, local, static, constant, this, that, pointer, temp

Question 5

What are the memory access commands?

Answer 5

Push segment index //push the value of segment[index] into stack
Pop segment index // pop the topmost element into segment[index]

Question 6

If I have a foo.vm file with 3 functions, what is the memory distribution?

Answer 6

Local, argument, this, that, pointer for each function. Static is shared between all the functions. Temp and constant are program wised

Question 7

From jack program of two classes foo.jack and Bar.jack with methods m,n,p and m,n- what are he products of the vim to assembly to hack?

Answer 7

2 files Foo.vm and Bar.vm with Foo.m, Foo.n Foo.p and Bar.m and Bar.n functions. After one prog.asm file
And then prog.hack binary code

Question 8

What is the memory distribution of the hack?

Answer 8

O-15 are 16 virtual registers // notice that everything is on the RAM!
16-255 are static variables
256-2047 is the stack
2048-16384 is the heap
16384-24575 is memory mapped I/O

Question 9

What are the 16 virtual registers?

Answer 9

SP RAM[0], LCL RAM[1], ARG RAM[2], THIS RAM [3], THAT RAM[4].
RAM[5-12] is temp, RAM[13-15] are general purpose

Question 10

How to do memory segment mapping from vm to asm?

Answer 10

We have the 4 virtual registers that are mapped to the RAM.
AnY entry to one of those segments should be translated as
: if to the i’th entry of LCL for example
(base + i).

Question 11

How does access to pointer memory should be decoded?

Answer 11

Pointer i should be treated as access RAM[3 +i]

Question 12

How does access to temp should be decoded?

Answer 12

temp i should be RAM[5 + i]

Question 13

How to write arithmetic command?

Answer 13

Pop = @sp, AM = M-1// A = memory[0] -1..takes the sp down
D=M//put the data in D
If binary...
@sp AM=M-1, A=M
Let's say add command
D=D+A
Now we should push D
@sp, A=M, M=D, @sp, M=M+1

Question 14

When implementing a call xxx operation, what is the return address?

Answer 14

The address of the next command in the caller’s code.

Question 15

What are the 3 program flow commands in the vm?

Answer 15

Label label
Goto label
If-goto label

Question 16

What is the label label command?

Answer 16

His command labels the current location in the function’s code. Only label locations can be jumped to from other parts of the program? The scope is the function where it is defined

Question 17

What is goto label command?

Answer 17

Effects an unconditional goto operation, causing execution to continue from the location marked by the label. The jump destination must be located at the same function

Question 18

What is if-goto label command?

Answer 18

The stack topmost element is popped. If the value is not zero, execution continues from the location marked by the label

Question 19

Method bar in class foo in jack language will be compiled to?

Answer 19

To a vm function named foo.bar

Question 20

What are the 3 function related commands?

Answer 20

Function f n
Call f m
Return

Question 21

What is the function

Function f n?

Answer 21

Here starts the code of a function named f that has n local variables.
Implemantation:
Repeat n times:
PUSH 0

Question 22

What is the function

Call f m?

Answer 22

Call function f, stating that m arguments have already been pushed onto the stack by the caller
Implementation:
Push return-address 
Push LCL
Push ARG
push THIS
push THAT
ARG = sp - m -5 //in order to reposition ARG TO THE called func
LCL = sp
Goto f
(return address)

Question 23

What is the function
Return?
FIX THIS PAGE 164

Answer 23

Return to the calling function
Implementation:
FRAME =LCL // frame is temporary
RET = *(FRAME - 5)
*ARG = pop()
Sp = ARG + 1
THAT = *(FRAME - 1)

Question 24

What is the protocol of the calling function?

Answer 24

1. The caller has to push as many arguments as needed
2. The caller invokes the function using the call command
3. After the called function has returned, the arguments that the caller pushed are no longer in the stack and the topmost element is the return parameter
4. After the called function returns, the caller’s memory segments argument, local, static,this,that,pointer are the same as they were and the temp segment is undefined!

Question 25

What is the called function protocol?

Answer 25

When it starts, it’s argument segment is already initialized with actual values and it’s local variables segment has been allocated and init to zeros.

2. The static segments the static segment of the vm file and the working stack is empty
3. The segments this, that, pointer and temp are undefined
4. Before return the called function must push an element into the stack

Question 26

What is a must to start a vm program?

Answer 26

Each vm program has to have Sys.init function.