some dodgy source code

[hooverphonique]

and the reason why it crashes on exit is, as mentioned before, that the program doesn't reply to the workbench message.

[mark_k]

How to get and reply to the WBStartup Message is covered in the Amiga ROM Kernel Manual: Libraries.

It's not too difficult:
- Get a pointer to your Process structure, either read the ThisTask field in ExecBase or call FindTask(0).
- Check the pr_CLI field. If that's zero, you're being run from Workbench.
- In that case, call GetMsg() on your pr_MsgPort. Save the return value.
- When your program exits, if you've been run from Workbench don't put a return value in D0 and RTS. Instead you need to call Forbid() then ReplyMsg() to the WBStartup message you saved earlier. Workbench handles unloading your program.

Steve: If you post your current source code I'll add support for being run from Workbench to it.

[Steve]

Originally Posted by mark_k

How to get and reply to the WBStartup Message is covered in the Amiga ROM Kernel Manual: Libraries.
Steve: If you post your current source code I'll add support for being run from Workbench to it.

Hehe. As I'm a bit lazy that's an offer too good to refuse. lol. However being at work, I don't have access to my code so will post it this evening around 7pm. The reason its not included in the book is the author didn't want to over-complicate things. He skips over a lot of details as its just an introduction to assembler. I have his other book 'Mastering Amiga Assembler' so will be starting on that next. Thanks.

[Steve]

Here is the latest source code.

[mark_k]

Here's a modified version with support for running from Workbench. I didn't assemble or test it yet.

Edit to add: To use FindTask instead of the ExecBase ThisTask field to get a pointer to your Task/Process, instead of

start		movea.l	_AbsExecBase.w,a6
		move.l	ThisTask(a6),a0

you can do this:

start		moveq	#0,d0
		CALLSYS	FindTask,_AbsExecBase
		movea.l	d0,a0

[Steve]

Originally Posted by mark_k

Here's a modified version with support for running from Workbench. I didn't assemble or test it yet.

Brilliant, that was quick. Will test it now.

[Steve]

It says missing close bracket on line 18. lea (pr_MsgPort,a0),a0

[mark_k]

Whoops I used new-style syntax for that line. You can change it to
lea pr_MsgPort(a0),a0
or alternatively/equivalently
adda.w #pr_MsgPort,a0

[Steve]

Thanks its getting there. I have had to add a few of the new library calls (like _LVOFindTask) to Defines2.i and I'm left with a couple of errors regarding pr_CLI and pr_MsgPort. Undefined symbol. Do I need to declare these as well?

Ok I managed to get it to compile and run properly by adding the 'INCLUDE dos/dosextens.i' line to the top of the program. Odd thing is it still says program failed suspend/reboot (on program exit) on my standard Wb 3.1 setup but still on my emulated uaegfx display it doesn't crash on exit. Strange but not really a big deal I guess.

[mark_k]

Can you post your current executable here, I'll take a look at it with ReSource (a disassembler).

[Steve]

Originally Posted by mark_k

Can you post your current executable here, I'll take a look at it with ReSource (a disassembler).

Ok, thanks. I just created a new executable and tried to run it again on my uaegfx wb setup and got the suspend/reboot message. Its like I'm not releasing some memory or something. Really odd. Anyway here is the new executable.

[mark_k]

D'oh! I used the wrong address register for ReplyMsg. (Why did Commodore use A0 for GetMsg, but A1 for ReplyMsg???)

Before CALLSYS ReplyMsg,_AbsExecBase change
movea.l d0,a0
to
movea.l d0,a1

[Steve]

Hehe. I bet these kind of mistakes are sooooo easy to make in assembler. I'm from a C++/Java programming background so all this low-level stuff is new to me. I will try it out tonight and let you know how I get on.

[Steve]

I made the change but this program seems determined to crash on exit. Oh well. Thanks for trying.

[mark_k]

Okay I think I missed one more thing. When you're getting the WBStartup message, you need to call WaitPort() before GetMsg(). At least, from looking at the code in several other programs that's what they do.

Also, what I said before about execution not returning to your program after you ReplyMsg() to the WBStartup message was wrong.

Change the start of your program to this:

start		moveq	#0,d0
		CALLSYS	FindTask,_AbsExecBase
		movea.l	d0,a2
		tst.l	pr_CLI(a2)
		bne.b	run_from_cli

		lea	pr_MsgPort(a2),a0
		CALLSYS	WaitPort,_AbsExecBase
		lea	pr_MsgPort(a2),a0
		CALLSYS	GetMsg,_AbsExecBase
		move.l	d0,wbstartupmsg			Save for later

run_from_cli	...

[Steve]

Still no joy. However I did find this in the how to code AGA docs:

3. Your code won't run from an icon.
====================================

You stick an icon for your new demo (not everyone uses the CLI!) and
it either crashes or doesn't give back all the RAM it uses. Why?

Icon startup needs specific code to reply to the workbench message.
With the excellent Hisoft Devpac assember, all you need to do is add
the line

    include "misc/easystart.i"

and it magically works!

For those without Devpac, here is the relevent code:

* some startup code to make a Workbench execute look like the CLI
* based loosely on RKM Vol 1 page 4-36

* Include this at the front of your program
* after any other includes
* note that this needs exec/exec_lib.i

	IFND	EXEC_EXEC_I
	include	"exec/exec.i"
	ENDC
	IFND	LIBRARIES_DOSEXTENS_I
	include	"libraries/dosextens.i
	ENDC


	movem.l	d0/a0,-(sp)		save initial values
	clr.l	returnMsg

	sub.l	a1,a1
	move.l    4.w,a6
	jsr	_LVOFindTask(a6)		find us
	move.l	d0,a4

	tst.l	pr_CLI(a4)
	beq.s	fromWorkbench

* we were called from the CLI
	movem.l	(sp)+,d0/a0		restore regs
	bra	end_startup		and run the user prog

* we were called from the Workbench
fromWorkbench
	lea	pr_MsgPort(a4),a0
	move.l    4.w,a6
	jsr	_LVOWaitPort(A6)		wait for a message
	lea	pr_MsgPort(a4),a0
	jsr	_LVOGetMsg(A6)			then get it
	move.l	d0,returnMsg		save it for later reply

* do some other stuff here RSN like the command line etc
	nop

	movem.l	(sp)+,d0/a0		restore
end_startup
	bsr.s	_main			call our program

* returns to here with exit code in d0
	move.l	d0,-(sp)		save it

	tst.l	returnMsg
	beq.s	exitToDOS		if I was a CLI

	move.l	4.w,a6
        jsr	_LVOForbid(a6)
	move.l	returnMsg(pc),a1
	jsr	_LVOPermit(a6)

exitToDOS
	move.l	(sp)+,d0		exit code
	rts

* startup code variable
returnMsg	dc.l	0

* the program starts here
	even
_main

[mark_k]

I think I've finally noticed what the problem is. Please just kill me if it still doesn't work after this change!

FindTask takes its argument in A1, not D0. So replace the moveq #0,d0 before calling FindTask with suba.l A1,A1 instead.

By the way, there's a typo in the code you quoted. It calls Permit instead of ReplyMsg at the end.

[Steve]

Hallelujah, praise the lord, IT WORKS!! Thank you!!

Program attached.

[Steve]

I'm not too sure what the line suba.l a1,a1 is actually doing. I understand it means subtract address. It seems to me that it is simply clearing the resister to 0 or is it more than that? If so why not just use move.l #0,a1?

[phx]

suba.l a1,a1 is shorter (2 bytes instead of 6 bytes) and faster (6 cycles instead of 12 cycles on the 68000).