This ought to be obvious

I’m trying to run the following and getting “abort on data transfer” at line -2.

If I remove the branch instruction, the error goes away. It makes no difference whether the target label exists or not.

What am I missing?

REM > WimpTest
size%=&1000
DIM code% size%
ON ERROR PROCerror
PROCasm
END

DEF PROCerror
  ON ERROR OFF
  REPORT: PRINT " at line ";ERL
  END
ENDPROC

REM =============================

DEF PROCasm
  FOR pass%=8 TO 11 STEP 3
    *REPORT \G pass% ~code% ~size%
     O%=code%
     P%=0
     L%=code%+size%
     [OPT pass%
     b skipdata
     .skipdata
     ]
   NEXT
 ENDPROC

Your two assembler passes are with OPT %1000 and OPT %1011, i.e. you have bit two clear. This means BASIC will write the output to P%, which in your case is 0. If you want the assembled code placed at O%, you need to have bit two set.

P%=0

P% is where the code will be assembled, 0 could be tricky.

There isn’t an OPT 8 to 11, it does the same as 0 to 3 – unless I was out that day. You want 4 to 7.

DEF PROCasm
  FOR pass%=12 TO 15 STEP 3
   *REPORT \G pass% ~code% ~size%
     O%=code%
     P%=0
     L%=code%+size%
     [OPT pass%
     b skipdata
     .skipdata
     ]
   NEXT
 ENDPROC

00000000                    OPT pass%
00000000 EAFFFFFF           b skipdata
00000004                    .skipdata
*

There isn’t an OPT 8 to 11, it does the same as 0 to 3 – unless I was out that day.

Bit 3 enables bounds checking against the value in L%, and has done since Arthur.

You want 4 to 7.

12 to 15, as David says, might be better.

Ah. I was out that day.

Yes, I realised aftyer reading trhe first answer that I had omitted the flag for offset assembly, but yused the values for it. 12 to 15 is what I intended to use.

Like I said – should have been obvious.

If in doubt, remember you can always use the %10101 style notation to make it clearer which bits are set.

use the %10101 style notation

I’m reminded of the firewall rule number I inserted the other day.
The triggering person being slightly annoying, but having convinced people things should pass may have a bearing on me choosing to insert at position 101.
It doesn’t drop packets.