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Old 29 April 2017, 22:23   #1
Nightfox
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Help with GetReg and PutReg

Hello guys

I was wanting help with being able to access the registers with putreg and getreg.

I expect the following code to output "The value in D1 is: 20" but instead it outputs "The value in D1 is: 0". What am I doing wrong here?

Code:
move.w #20,d1
PutReg d1,test.w
NPrint "The value in D1 is: ", test
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Old 30 April 2017, 02:30   #2
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Not entirely sure... It works fine here.
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Old 30 April 2017, 11:13   #3
AlgoRythmic
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Tested it and works fine in BB 2.1 also.
Did you try to declare the variable before using it in putreg?

like so:
Code:
test.w
move.w #20,d1
PutReg d1,test
NPrint "The value in D1 is: ", test
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Old 30 April 2017, 20:39   #4
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OK the code seems to work except for when it's inside a statement. I wanted to do assembly inside a statement but it's not working for some reason.
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Old 30 April 2017, 21:50   #5
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Quote:
Originally Posted by sacredbanana View Post
OK the code seems to work except for when it's inside a statement. I wanted to do assembly inside a statement but it's not working for some reason.
Ript^DisasterArea came across this problem pretty early on when he was adding his assembly routines to our Blitz based engine. There were a couple of crude workarounds, I honestly cannot recall what they were though.

If you have the technical expertice you can make your own Blitz Commands library, but if it's just a routine that you only need to use in one particular program then this may be more trouble than it's worth.

Also don't be surprised when your code fails if you try to use all the registers. I cannot recall exactly which ones, but I'm pretty sure that we just stayed away from the upper four address and data registers as much as possible.
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Old 30 April 2017, 21:59   #6
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In a statement the registers d0-d5 are automatically set by the first 5 parameters given to the function. the rest goes onto the stack iirc. Also it is a good idea to 'unlk a4' at the beginning of the asm code and return with 'asmexit'.
i have to reread the chapter, but afaik that could be the problem somehow.
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Old 30 April 2017, 22:40   #7
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Quote:
Originally Posted by Cylon View Post
In a statement the registers d0-d5 are automatically set by the first 5 parameters given to the function. the rest goes onto the stack iirc. Also it is a good idea to 'unlk a4' at the beginning of the asm code and return with 'asmexit'.
i have to reread the chapter, but afaik that could be the problem somehow.
I put a MouseWait after the NPrint line and when I do unlk a4 the NPrint reports the value as 16492 and as soon as I click the mouse the OS crashes with a software error.
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Old 01 May 2017, 03:01   #8
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Basically it is never a good idea to mix asm with BB2 cmds, especially when your setup seems to be messed up in some other way. When you are able to code in asm then keep it strictly asm and only return the result you need from the function. Avoid mixing e.g. Print (which involves several different libs) with the asm code. Probably the debugger gets fucked up while trying to figure out whats going on in there.
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Old 01 May 2017, 17:21   #9
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I hope there is an easy workaround because otherwise I think I'll just stick with learning pure assembly
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Old 01 May 2017, 18:06   #10
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I hope there is an easy workaround because otherwise I think I'll just stick with learning pure assembly
As I understand from this thread, the problem with mixing assembly and basic is in statements. You can create statements with only assembly code in them, and call them from basic.
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Old 01 May 2017, 18:52   #11
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This is annoying but I can probably work with this. I just therefore need to know how to obtain the address of an array so I can put it in an address register. Anyone know how?
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Old 01 May 2017, 22:33   #12
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The address of any variable can be obtained using the & symbol:

Address.l = &MyVariable.w

You can't get an address for an array specifically, but you can get the address of the first element using:

Address.l = &MyArray(0)
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Old 02 May 2017, 01:14   #13
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Thanks so much! I just wrote an InsertionSort program in Blitz except the actual statement that does the actual sorting is in pure assembly! I used Blitz to read a text file containing a list of numbers and my assembly statement sorts the numbers.
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Old 02 May 2017, 21:38   #14
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Quote:
Originally Posted by Cylon View Post
Basically it is never a good idea to mix asm with BB2 cmds, especially when your setup seems to be messed up in some other way. When you are able to code in asm then keep it strictly asm and only return the result you need from the function. Avoid mixing e.g. Print (which involves several different libs) with the asm code. Probably the debugger gets fucked up while trying to figure out whats going on in there.
I seem to recall that setting up the display in Blitz, compiling the code and then dissassembling the code to use in a proper assembler seemed to be somewhat effective. Blitz can make some pretty fancy copper tricks quite easy to set up. But then there's the issue with mixing Blitz commands with ASM so this was how we approached the issue I seem to recall.

Also writing your own command library in 68k can be another thing you might like to consider.

Or assemble the routine you want into an executable, include it with IncBin and call it from your code is another approach to this problem.

But I have actually found that certain commands like JSR, LSL, etc. can be used instead of their Basic style equivalents no problems, just long and elaborate sections of 68K code will probably fail unless you are very careful.
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Old 03 May 2017, 03:15   #15
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'Careful' is the word of the day, imho. You have to understand how a compiler works: A simple cmd might cause a stack swap, malloc, register chg or whatever while you still think you are just swapping some asm register value or whatever.
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