Part Diary of an ASM Learner - Page 2

musashi5150 · 19 January 2007, 18:58

Yup, I agree EQU is very useful in making your code both easier to read and manage. If any of you guys know any C/C++ you could say EQU is very much like #define in some respects.

Just as an example when loading a colour register it's much easier to read your code when you are doing something like:

Code:

COLOR        EQU    $dff180
 
 
             move.w d0,COLOR

than

Code:

             move.w d0,$dff180

It's best to bear this stuff in mind NOW so you don't start bad habits.

BippyM · 19 January 2007, 19:03

Everything I've posted thus-far is discussed later in the book i'm reading. I'll naturally cover it when I get that far

pbareges · 19 January 2007, 19:49

Quote:

Originally Posted by musashi5150

EQU is used for contants that never change
DS.x is used to Define Storage (uninitialised) - you can change this when running
DC.x is used for Define Constant (initialised) - you can change this when running

Example:

Code:

        ds.b    4    ;Reserves 4 bytes storage (contains random trash data)
        dc.b    4    ;Reserves 1 byte storage and puts the value '4' into it
beefy   equ     4    ;Reserves NO storage, but you can use the word 'beefy' to mean 4 in your program code...

thanks for you clear explanation!! but you should agree thay dc.l 1 does not allocate 1 long variable only (as described in bippym code)..it allocates 1 long variable and puts the value 1 in it ...right? (infact the 1 value is confusing,,)

BippyM · 19 January 2007, 20:43

ds.b 1 will allocate 1 byte in memory
ds.w 1 will allocate 2 bytes
ds.l 1 will allocate 4 bytes

The allocated memory will be empty and just the address associated with the name

Joe Maroni · 19 January 2007, 21:39

in nearly every assembler command the amount of bytes is stored via:

xxx.b -> 1 byte
xxx.w -> 2 bytes
xxx.l -> 4 bytes

and there is a special "form" of "type" the nibble...

xxx.s -> 1/2 byte -> 4 bits

just to mention it...

and the dc.x "command" (it´s not really a command !!) is neccessary for PC relative coding !!!!

StingRay · 20 January 2007, 00:37

Quote:

Originally Posted by x_to

and there is a special "form" of "type" the nibble...

xxx.s -> 1/2 byte -> 4 bits

Which assembler would allow that?

Quote:

Originally Posted by x_to

and the dc.x "command" (it´s not really a command !!) is neccessary for PC relative coding !!!!

Could you please explain what you mean here? I don't see why dc.x is necessary for pc relative coding. Because "necessary" means pc-relative coding would not be possible without dc.x which is of course plain wrong. So I guess you meant something like calculating jump distances for some jumptables (dc.w rout1-base, dc.w rout2-base etc) but I am not sure about that. So please explain what you mean here because I think it's a pretty confusing/wrong statement you made.

BippyM · 20 January 2007, 12:53

This thread is going to get too complex too quickly.

I have not mention (pcP relative coding yet but it will be covered.

I'll also be covering other area's, just give it time and please you seasoned asm guys, if you mention something new explain it!

BippyM · 20 January 2007, 14:32

Code:

        add.<size> source,destination

Add simply adds the contents of the source to the contents in the destination

an example

Code:

        move.l    NUMBER1,d0        Copy contents of NUMBER1 into d0
        add.l    d0,NUMBER2        Add the contents of d0 to that already in NUMBER2
        rts
NUMBER1    dc.l    3            Set NUMBER1 to 3
NUMBER2    dc.l    4            set NUMBER2 to 4

WHat do you think the value in NUMBER2 will be?

That is pretty much all the book covers on arithmetic, though there will be more i'm sure

BippyM · 20 January 2007, 14:52

The following new commands will be used here

Code:

lea source address, register
moveq source, destination
subq source,destination
beq address
bne address
bra address

LEA - load Effective Address allows the programmer to load an address into a specified register

Code:

lea NEW_WINDOW,a0

This will load the location in memory which has been labelled NEW_WINDOW into register a0

Loops

Loops have 4 identifiable sections

Initialisation ; Setup and initialise the loop
Processing ; The main body of the loop
Control ; Decide whether further iterations af the loop are required
Terminal ; Terminates the loop

There are two types of loop post-test and pre-test, the difference is where the exit from the loop is made. In the pre-test the check is made before the loop is executed and if it is satisfied the loop will never run. In the post-test the check is made at the end of the loop, so the main body of the loop is always executed at least once.

Code:

post-test loop

    moveq    #10,d0        put 10 into d0
LOOP    MAIN BODY        ; here is where the main body of the loop would be
    subq    #1,d0        ; Subtract 1 from d0
    bne    LOOP        ; if d0 doesn't equal 0 then loop

to write the exacty same loop in pre-test form the code would look something like

Code:

pre-test loop

	moveq	#10,d0		put 10 into d0
LOOP	beq	LOOP_END	if d0 equals 0 jump past loop

	MAIN BODY		; here is where the main body of the loop would be
	
	subq	#1,d0		; Subtract 1 from d0
	bra	LOOP		; branch back and loop

LOOP_END

More on loops later

pbareges · 20 January 2007, 20:53

thanks bippy ...what would be the difference between moveq and move.l ?

WayneK · 21 January 2007, 01:18

moveq is the "quick" version, only used for values +/- 128, but it takes less cpu cycles than the normal move...

BippyM · 23 January 2007, 12:26

Some asm stuff i found on the net

BippyM · 24 January 2007, 15:20

One way to store characters in memory would be to store a count of the number of characters in the string.

Code:

TEXT    dc.b    5,"HELLO"

another method could use a NULL (0) terminating charcter

Code:

TEXT    dc.b    "HELLO",0

the 0 (zero) represents the end of the string. This method is better as longer strings don't need to be pre-calculated

We shall program a routine which will convert the pre-calculated method to the 0 terminating method.

We need to start by loading a register with the address of the first character which we can then copy into d0.

Code:

      lea    TEXT,a0    load a0 with start address of TEXT
      move.b (a0),d0    Copy character count into d0

We need to reserve memory space for the string and the terminating character. We know the string is 5 characters and we need a 6th for the terminating 0 so the following is going to be needed

Code:

COPY    ds.b    6    Reserve 6 bytes for the copy and terminating 0

next we put the astart address of COPY into a1 so we know where to start copying to

Code:

    lea    COPY,a1    Address of destination into a1

Now a0 is pointing to the 5 in the source string (which is the start of the string incidentally) and a1 is pointing to the start of the reserved space for the copy to go into.

We need to move the address of a0 to point to the first letter of the string so the following code needs to be included

Code:

    addq.l    #1,a0    ; increas address in a0 by 1

We now have the following basic framework

Code:

        lea        TEXT, a0        Put start address of TEXT into a0
        move.b     (a0), d0        Copy Char count to d0 (5)
        addq.l     #1, a0          Increase a0 address by 1
        lea        COPY, a1        Start address of dest into a1

        <Main Loop, Not Yet written>

        rts

TEXT        dc.b    5,"HELLO"
COPY        ds.b    6

The main loop itself can be written using indirect addressing to copy the string. the first line is saying "Copy the contents of the byte whose address is being pointed to by a0 to the address being pointed to by a1" then reduce the loop counter (d0) by 1

Code:

    move.b (a0),(a1)        copy contents of a0 to a1
    subq.b #1,d0            reduce count by 1

Obviously a0 and a1 need incrementing to point to the next memory location so

Code:

    addq.l    #1,a0        increase a0 by 1

and the same for a1

When d0 equals 0 (zero) then the loop is effectively over so a BNE (Branch Not Equal) loop can be used

our loop now looks like

Code:

LOOP    move.b    (a0),(a1)        Copy contents of a0 to a1
        addq.l    #1,a0            Increase address by 1
        addq.l    #1,a1            and again fore a1
        subq.b    #1,d0            decrease count by 1
        bne       LOOP             if d0<>0 loop

After all that we need to add the terminal 0 (NULL) so the following will do once the loop has exited

Code:

    move.b    #0,(a1)     add termination

Does someone (A newbie) want to write the complete routine?

(and before someone says yes I know there are quicker and better ways of doing this ((a0)+ etc), and that is next so please keep quiet!)

BippyM · 24 January 2007, 16:03

is anyone finding this useful?

StingRay · 24 January 2007, 16:16

I find it interesting to read, even though I know my 68k asm pretty well by now.

BippyM · 24 January 2007, 16:22

Quote:

Originally Posted by StingRay

I find it interesting to read, even though I know my 68k asm pretty well by now.

Cool, it's pretty simple stuff really, esp to the experts

killergorilla · 24 January 2007, 16:24

I'm reading every post, makes interesting reading

@Bip: can't remember what I wanted on IRC...

StingRay · 24 January 2007, 16:58

Quote:

Originally Posted by bippym

Cool, it's pretty simple stuff really, esp to the experts

Yeah, that's what makes it somehow interesting since it reminds me of the time 17 years ago when I learned 68k asm.

When I saw the stringcopy loop the first I wanted to post is how to make it better but then I saw your post and kept quiet.

Somehow funny.

pbareges · 24 January 2007, 17:39

keep up with your great project! amazing

superBuster · 25 January 2007, 01:49

god dang... now I'm gonna have to learn asm..... bastards....

19 January 2007, 18:58	#21
musashi5150 move.w #$4489,$dff07e Join Date: Sep 2005 Location: Norfolk, UK Age: 42 Posts: 2,351	Yup, I agree EQU is very useful in making your code both easier to read and manage. If any of you guys know any C/C++ you could say EQU is very much like #define in some respects. Just as an example when loading a colour register it's much easier to read your code when you are doing something like: Code: COLOR EQU $dff180 move.w d0,COLOR than Code: move.w d0,$dff180 It's best to bear this stuff in mind NOW so you don't start bad habits.

20 January 2007, 14:32	#28
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Simple arithmetic Code: add.<size> source,destination Add simply adds the contents of the source to the contents in the destination an example Code: move.l NUMBER1,d0 Copy contents of NUMBER1 into d0 add.l d0,NUMBER2 Add the contents of d0 to that already in NUMBER2 rts NUMBER1 dc.l 3 Set NUMBER1 to 3 NUMBER2 dc.l 4 set NUMBER2 to 4 WHat do you think the value in NUMBER2 will be? That is pretty much all the book covers on arithmetic, though there will be more i'm sure

20 January 2007, 14:52	#29
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Loops The following new commands will be used here Code: lea source address, register moveq source, destination subq source,destination beq address bne address bra address LEA - load Effective Address allows the programmer to load an address into a specified register Code: lea NEW_WINDOW,a0 This will load the location in memory which has been labelled NEW_WINDOW into register a0 Loops Loops have 4 identifiable sections Initialisation ; Setup and initialise the loop Processing ; The main body of the loop Control ; Decide whether further iterations af the loop are required Terminal ; Terminates the loop There are two types of loop post-test and pre-test, the difference is where the exit from the loop is made. In the pre-test the check is made before the loop is executed and if it is satisfied the loop will never run. In the post-test the check is made at the end of the loop, so the main body of the loop is always executed at least once. Code: post-test loop moveq #10,d0 put 10 into d0 LOOP MAIN BODY ; here is where the main body of the loop would be subq #1,d0 ; Subtract 1 from d0 bne LOOP ; if d0 doesn't equal 0 then loop to write the exacty same loop in pre-test form the code would look something like Code: pre-test loop moveq #10,d0 put 10 into d0 LOOP beq LOOP_END if d0 equals 0 jump past loop MAIN BODY ; here is where the main body of the loop would be subq #1,d0 ; Subtract 1 from d0 bra LOOP ; branch back and loop LOOP_END More on loops later Last edited by BippyM; 20 January 2007 at 15:45.

23 January 2007, 12:26	#32
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Some asm stuff i found on the net Last edited by BippyM; 10 July 2013 at 23:00.

24 January 2007, 15:20	#33
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	String Conversion One way to store characters in memory would be to store a count of the number of characters in the string. Code: TEXT dc.b 5,"HELLO" another method could use a NULL (0) terminating charcter Code: TEXT dc.b "HELLO",0 the 0 (zero) represents the end of the string. This method is better as longer strings don't need to be pre-calculated We shall program a routine which will convert the pre-calculated method to the 0 terminating method. We need to start by loading a register with the address of the first character which we can then copy into d0. Code: lea TEXT,a0 load a0 with start address of TEXT move.b (a0),d0 Copy character count into d0 We need to reserve memory space for the string and the terminating character. We know the string is 5 characters and we need a 6th for the terminating 0 so the following is going to be needed Code: COPY ds.b 6 Reserve 6 bytes for the copy and terminating 0 next we put the astart address of COPY into a1 so we know where to start copying to Code: lea COPY,a1 Address of destination into a1 Now a0 is pointing to the 5 in the source string (which is the start of the string incidentally) and a1 is pointing to the start of the reserved space for the copy to go into. We need to move the address of a0 to point to the first letter of the string so the following code needs to be included Code: addq.l #1,a0 ; increas address in a0 by 1 We now have the following basic framework Code: lea TEXT, a0 Put start address of TEXT into a0 move.b (a0), d0 Copy Char count to d0 (5) addq.l #1, a0 Increase a0 address by 1 lea COPY, a1 Start address of dest into a1 <Main Loop, Not Yet written> rts TEXT dc.b 5,"HELLO" COPY ds.b 6 The main loop itself can be written using indirect addressing to copy the string. the first line is saying "Copy the contents of the byte whose address is being pointed to by a0 to the address being pointed to by a1" then reduce the loop counter (d0) by 1 Code: move.b (a0),(a1) copy contents of a0 to a1 subq.b #1,d0 reduce count by 1 Obviously a0 and a1 need incrementing to point to the next memory location so Code: addq.l #1,a0 increase a0 by 1 and the same for a1 When d0 equals 0 (zero) then the loop is effectively over so a BNE (Branch Not Equal) loop can be used our loop now looks like Code: LOOP move.b (a0),(a1) Copy contents of a0 to a1 addq.l #1,a0 Increase address by 1 addq.l #1,a1 and again fore a1 subq.b #1,d0 decrease count by 1 bne LOOP if d0<>0 loop After all that we need to add the terminal 0 (NULL) so the following will do once the loop has exited Code: move.b #0,(a1) add termination Does someone (A newbie) want to write the complete routine? (and before someone says yes I know there are quicker and better ways of doing this ((a0)+ etc), and that is next so please keep quiet!)

19 January 2007, 19:03	#22
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	Everything I've posted thus-far is discussed later in the book i'm reading. I'll naturally cover it when I get that far

19 January 2007, 20:43	#24
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	ds.b 1 will allocate 1 byte in memory ds.w 1 will allocate 2 bytes ds.l 1 will allocate 4 bytes The allocated memory will be empty and just the address associated with the name

19 January 2007, 21:39	#25
Joe Maroni Moderator Join Date: Feb 2003 Location: Germany Age: 44 Posts: 1,303	in nearly every assembler command the amount of bytes is stored via: xxx.b -> 1 byte xxx.w -> 2 bytes xxx.l -> 4 bytes and there is a special "form" of "type" the nibble... xxx.s -> 1/2 byte -> 4 bits just to mention it... and the dc.x "command" (it´s not really a command !!) is neccessary for PC relative coding !!!!

20 January 2007, 12:53	#27
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	This thread is going to get too complex too quickly. I have not mention (pcP relative coding yet but it will be covered. I'll also be covering other area's, just give it time and please you seasoned asm guys, if you mention something new explain it!

20 January 2007, 20:53	#30
pbareges Registered User Join Date: Feb 2005 Location: montreal / canada Age: 47 Posts: 722	thanks bippy ...what would be the difference between moveq and move.l ?

21 January 2007, 01:18	#31
WayneK Registered User Join Date: May 2004 Location: Somewhere secret Age: 50 Posts: 364	moveq is the "quick" version, only used for values +/- 128, but it takes less cpu cycles than the normal move...

24 January 2007, 16:03	#34
BippyM Global Moderator Join Date: Nov 2001 Location: Derby, UK Age: 48 Posts: 9,355	is anyone finding this useful?

24 January 2007, 16:16	#35
StingRay move.l #$c0ff33,throat Join Date: Dec 2005 Location: Berlin/Joymoney Posts: 6,863	I find it interesting to read, even though I know my 68k asm pretty well by now.

24 January 2007, 16:24	#37
killergorilla Lesser Talent Join Date: Jan 2003 Location: UK Age: 42 Posts: 7,957	I'm reading every post, makes interesting reading @Bip: can't remember what I wanted on IRC...

24 January 2007, 17:39	#39
pbareges Registered User Join Date: Feb 2005 Location: montreal / canada Age: 47 Posts: 722	keep up with your great project! amazing

25 January 2007, 01:49	#40
superBuster superFreak Join Date: Dec 2006 Location: planet earth Age: 51 Posts: 157	god dang... now I'm gonna have to learn asm..... bastards....

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