Address Region Size

[65816]

A possible feature request.

Assign an address region size to a label

or

When editing a data operand allow addition or subtraction.

I have this block of code:

MOVE1           .dd2  BLOCK1          ;source address
                .dd2  $6800           ;destination address
                .dd2  $051c           ;number of bytes to copy
MOVE2           .dd2  BLOCK3          ;source address
                .dd2  $1000           ;destination address
                .dd2  $016b           ;number of bytes to copy
MOVE3           .dd2  BLOCK2          ;source address
                .dd2  $1800           ;destination address
                .dd2  $03ae           ;number of bytes to copy

The size of each block is referenced by number of bytes to copy comment. The block size can also be computed by the following:

MOVE1 bytes to be copied: block2 - block1 - 1
MOVE2 bytes to be copied: block4 - block3 (block4 is a label after block3 region ending)
MOVE3 bytes to be copied: block3 - block2

If I adjust MOVE3 bytes to be copy value to BLOCK3, 6502bench computes the offset.

MOVE3           .dd2  BLOCK2          ;source address
                .dd2  $1800           ;destination address
                .dd2  BLOCK3-$26ff    ;number of bytes to copy

To this, maybe

MOVE3           .dd2  BLOCK2          ;source address
                .dd2  $1800           ;destination address
                .dd2  BLOCK3-BLOCK2    ;number of bytes to copy

or

MOVE3           .dd2  BLOCK2          ;source address
                .dd2  $1800           ;destination address
                .dd2  BLOCK3_SIZE    ;number of bytes to copy

[65816]

BLOCK1: 21E2
BLOCK2: 26FF
BLOCK3: 2AAD
BLOCK4: 2C18

[fadden]

This is currently in the "to do" list:

• Support expressions.
  • Start with simple expressions, such as ORing of multiple constants or defining an offset as the difference between two symbols.
  • Add "define offset table" that takes a base address and creates 8-bit or 16-bit offsets to symbols.
  • Allow arbitrary expressions in places that currently accept symbols (instruction and data operands). This is straightforward to manage within SourceGen, but can be difficult to generate for all cross-assemblers if the complexity gets too high.

The situation comes up fairly often, e.g. the byte count in the first tutorial would be best expressed as the difference between two labels. I think of it has a step in the direction of general expression handling... it's much simpler than support for arbitrary expressions, but it handles what is probably the most common use case.

One quirk of address region sizes is that, thinking in terms of how the source code would be written, you'd want to subtract the value of a label that is placed after the region from the label at the start of a region. So we might need to define post-labels to go with the pre-labels.

[fadden]

Moved to TO DO list.