[Coco] Need help with Assembler Program

[Robert Gault]

Charles Shrader wrote:
> Greetings!
> 
> I'm playing with EDTASM++ in an emulator (I've just ordered a real
> cartridge from Cloud-9) and am having
> Some problems with an "example" program I found on the internet.
> 
> When I assemble, I get no errors.  But when I try to execute the
> program, I get unusual results.
> 
> I'm wondering if the subroutines I'm referencing aren't located where
> this listing shows them.
> 
> I'm running on Dave Kiel's Coco 2 emulator.  Here are some of the
> subroutines that this program calls:
> 
> JSR	43304 -   this is supposed to do a CLS routine.
> JSR	[40962] - this should be a CHROUT subroutine.
> 
> I take it that an address in brackets [] is a relative address - the
> data at memory location 40962 is
> a pointer to the actual location of the CHROUT subroutine?
> 
> I'm wondering if these subroutine locations are actually for a Coco3
> perhaps??
> 
> The entire test program I'm trying to get running is:
> 
> 
> 00100 START    JSR     43304           CLS SUBROUTINE 
> 00110          LDA     #65             ASCII A 
> 00120 AGAIN    JSR     [40962]         CHROUT SUBROUTINE 
> 00130                  INCA            NEXT IN ALPHABET 
> 00140                  CMPA    #91     ONE PAST ASCII Z? 
> 00150                  BNE     AGAIN 
> 00160                  LDA     #32     ALPHABET DONE 
> 00170                  LDB     #6      PRINT 6 SPACES 
> 00180 REPEAT   JSR     [40962] 
> 00190                  DECB 
> 00200                  BNE     REPEAT 
> 00210 LOOP      BRA    LOOP 
> 00210                  END 
> 
> 
> Chuck

First, that is not relative addressing but extended indirect. You are 
correct about what [address] does.

The program looks good and would work except for some very important 
caveats. Where will the program be located in memory? How do you know 
were to go to get the program to start? Is the program going to be run 
from EDTASM's ZBUG or from Basic?

  As listed the program does not have an ORG (origin) statement. That 
means you have no way to predict where it will reside in memory. It 
won't matter much if run from ZBUG but there could be other problems. If 
run from ZBUG, you may overwrite part of the EDTASM program code.
  I suggest you make the following changes.

	ORG	$7000
00100 START    JSR     43304           CLS SUBROUTINE
...
00210                  END	START

These changes will tell EDTASM that the program should reside in memory 
starting at $7000. It also tells EDTASM that an info block at the end of 
the program should contain the execution address START. Run the program 
from Basic as follows:
10 CLEAR 200,&H7000
20 LOADM"TEST":EXEC

Just use whatever name the program is saved as. The clear statement will 
reserve space in memory above $7000 for the program. Since the program 
now contains the execution address, EXEC will start it.