Assembler Addressing Error - PJ Monty

pjv · 2006-12-14 22:43

Hello PJ;

I believe I have discovered a bug in the SX assembler's label addressing assignments.

For convenience,·I use a macro that automatically adds a "PAGE" instruction to a jump (or call) address (only) when the addressed location is not on the current page. This saves some memory and execution cycles compared to always adding a PAGE instruction before a jump or a call.
I name this macro jmp@, and invoke it as:

Address1··· jmp@··· Address2

and define it as:

jmp@·· ·macro···································· ;
··· ······ TargetPage = \1 >> 9··············· ;calculate page of the target address
······ ··· CurrentPage = $ >> 9··············· ;calculate page of current address counter
········· ·if TargetPage = CurrentPage······ ;test for same
············ ·jmp··· \1····························· ;if same then only issue jump instruction
··· ······ else······································· ;
······ ······ page· \1·······························;if different then issue page and jump instruction
········· ··· jmp··· \1
········· ·endm

This works great until the targetted address actually spans a page boundary, and the PAGE instruction is issued.·When that occurs,·the assembler miscalculates the address of the target by one location.
I did some experimentation, adding some superfuous instructions to the macro, and it turns out that the magnitude of the address error is the difference in size (number of instructions) between the "if" and "else" halves of the macro...... one in my case.

I have exhaused my ideas in how to "fool" the assembler using org statemnets, messing with the program counter·and so on, but no success in that so far.

Could you have a peek and correct that bug?

And if you really wanted to make us all thrilled, why not have the assembler thake care of issuing the necessary PAGE statements (only) when required? This could be a selectable configuration option.

Thanks for your consideration.

Cheers,

Peter (pjv)

P.S.· I for got to mention that when the address calculation is in error, all address labels further down are also off by that amount.

Post Edited (pjv) : 12/15/2006 6:14:52 PM GMT

PJMonty · 2006-12-16 00:16

Peter,

Let me look into what the problem is in SASM so I know what I am up against.

Thanks, PeterM

Peter Verkaik · 2006-12-16 00:48

I mentioned this problem some time ago and there was no easy solution then.
http://forums.parallax.com/showthread.php?p=527026

regards peter

pjv · 2006-12-16 01:10

Hi Peter V;

Yes, I see you describe exactly what I have re-discovered.

When I ran into this, I thought it was a remnant of the similar @jmp / @call adress calculation error I discovered in early 2005. Apparently not so, and perhaps there is no practical answer...... hopefully PJ can find something, but it's not the end of the world.

Just as long as everyone is very aware!

Cheers,

Peter (pjv)

PJMonty · 2006-12-16 08:48

Peter(s),

I thought this one sounded familiar. As far as I can tell, I fixed this one February 21, 2005 in SASM version 1.51.06. Here is a snippet of the list file I get using SASM 1.51.07, which part of the IDE version 3.1 and higher:

    53  0206  0012                  page NextPage ; Manually insert the page instruction
    54  0207  0A00                  jmp NextPage
    55                  
    56                  Address1    jmp@ NextPage ;Automatically insert the page instruction
    57  =00000002    m             TargetPage = NextPage >> 9                ;calculate page of the target address
    58  =00000001    m             CurrentPage = $ >> 9                ;calculate page of current address counter
    59               m             if TargetPage = CurrentPage       ;test for same
    60               m                jmp    NextPage                              ;if same then only issue jump instruction
    61               m             else                                        ;
    62  0208  0012   m                page  NextPage                               ;if different then issue page and jump instruction
    63  0209  0A00   m                jmp    NextPage
    65                    
    66                  
    67                  ;Address2   jmp@ SamePage
    68  020A  0B98                  jmp SamePage
    69                  
    70  =00000398           org $398
    71  =00000398       SamePage
    72                  
    73  =00000400           org $400
    74                  
    75  =00000400       NextPage

Lines 62 and 63 show the macro in action where it inserts the page instruction and generates a JMP command of "0A00".

Lines 53 and 54 show me manually inserting the page and doing the JMP and getting the same result. I put the manual version before the macro to avoid the potential problem where said all subsequent addresses were off by one.

I have attached my source file. Am I misunderstanding something (or making a mistake on my end) about this problem?

BTW, there does seem to be a problem when no page is required from the macro. In that case, I am getting a crash in SASM which I am investigating.

Thanks, PeterM

Peter Verkaik · 2006-12-16 08:54

The endif for·the if inside the macro is missing.
That gives a SASM DLL error, hence a crash.

regards peter

PJMonty · 2006-12-16 09:11

Peter (pjv),

I found the problem with the crash when no page was needed - the macro you show in your original post has an "if" without a corresponding "endif". Obviously SASM should handle this correctly with a warning, but there is something about the if/else being inside a macro that causes the crash before SASM can figure out it is missing the "endif". I'll see if I can fix that bug, but for now at least I don't have crashes with the macro whether it is adding a "page" or not.

Thanks, PeterM
Updated - I see I posted my message after you posted yours, hence the re-discovery of the missing "endif".

Assembler Addressing Error - PJ Monty

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