Assembler
options
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Assembler
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The OPT keyword denotes how the following block of assembler should be handled. It
relates to every block separately, so you must put the OPT keyword at the start of
each block. For example:
FOR loop% = 0 TO 2 STEP 2
P% = code%
[ OPT loop%
... some basic initialization stuff here ...
]
IF computer_is_networked% THEN
[
OPT loop%
... network code ...
]
ELSE
[
OPT loop%
... non-network code ...
]
ENDIF
[ OPT loop%
... the rest of the code ...
]
NEXT
This is a rough example showing how different bits of code can be utilised depending upon the
current conditions (and the code need not be the same number of instructions either!); and it
shows how you must use the OPT keyword - even if you only have one loop. However
the power and complexity of BASIC can be utilised to build up all kinds of fancy code.
The OPT parameters have the following meanings:
Bit 0 - Produce a listing during the compilation
Bit 1 - Report errors, such as unresolved references
Bit 2 - Offset assembly, if code is compiled for
execution at a different place to where it
currently is.
Bit 3 - Range check, will report if the code being
compiled overshoots the memory allocated.
Bit 4 - Enables the 'new' instructions.
A list of them is here.
Bit 8 - If set, the SWI "OS_SynchroniseCacheAreas" is not
called after compilation.
(does anybody know when this was introduced? RISC OS 3.7?)
Option List Err Offs RChk
--------------------------------
OPT 0 No No No No <-- First pass
OPT 1 Yes No No No
OPT 2 No Yes No No <-- Second pass
OPT 3 Yes Yes No No
OPT 4 No No Yes No
OPT 5 Yes No Yes No
OPT 6 No Yes Yes No
OPT 7 Yes Yes Yes No
OPT 8 No No No Yes <-- Alt. first pass
OPT 9 Yes No No Yes
OPT 10 No Yes No Yes <-- Alt. second pass
OPT 11 Yes Yes No Yes
OPT 12 No No Yes Yes
OPT 13 Yes No Yes Yes
OPT 14 No Yes Yes Yes
OPT 15 Yes Yes Yes Yes
OPT 16 No list, no error reporting, no offset assembly,
no range check, but will use new instructions.
...through to...
OPT 31 List, error reporting, offset assembly, range
checking, and uses the new instructions.
The first two option codes indicated are common values
used when compiling code.
The alternative option codes are identical, except that
range checking is enabled. This is useful for reporting
if the code is larger than the space allocated.
To include new instructions in a program, instead of
doing:
FOR loop% = 0 TO 2 STEP 2
P% = code%
[ OPT loop%
You would do:
FOR loop% = 16 TO 18 STEP 2
P% = code%
[ OPT loop%
BXR0" a branch to label XR0, or is it a thumb instruction?).
So RISC OS 4 now has this selectable with a bit in the options.
A lot of the functionality here is duplicated by Darren Salt's ExtBASasm module. To give you an example, the instruction in italics is NOT supported by ExtBASasm (there's only one). The rest are...
Links take you to places where you can find out more about the linked instruction.
The new instructions are:
ARM7 / StrongARM extensions