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Irmen de Jong
2026-02-26 01:44:36 +01:00
parent 08e3652924
commit 63cba4825a
3 changed files with 10 additions and 7 deletions
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docs/source/programming.rst
+9 -5
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@@ -1186,12 +1186,14 @@ Such subroutines are defined with ``asmsub`` like this::
the statement body of such a subroutine can only consist of just inline assembly.
The ``@ <register>`` part is required for rom and assembly-subroutines, as it specifies for the compiler
what cpu registers should take the routine's arguments. You can use the regular set of registers
The ``@ <register>`` part is required for rom and assembly-subroutines, as it specifies the
cpu registers that take the arguments. You can use the regular set of registers
(A, X, Y), special 16-bit register pairs to take word values (AX, AY and XY) and even a processor status
flag such as Carry (Pc).
It is not possible to use floating point arguments or return values in an asmsub.
.. note::
It is currently not possible to use floating point return values in an asmsub.
A floating point parameter is fine though and you can use the register FAC1 or FAC2 for that.
.. note::
Asmsubs can also be tagged as ``inline asmsub`` to make trivial pieces of assembly inserted
@@ -1238,8 +1240,10 @@ External subroutines are usually defined by compiler library files, with the fol
-> bool @Pc, ubyte @ A, ubyte @ X, ubyte @ Y
This defines the ``LOAD`` subroutine at memory address $FFD5, taking arguments in all three registers A, X and Y,
and returning stuff in several registers as well. The ``clobbers`` clause is used to signify to the compiler
what CPU registers are clobbered by the call instead of being unchanged or returning a meaningful result value.
and returning stuff in several registers as well. The ``clobbers`` clause is used to tell what CPU registers
are clobbered by the call instead of being unchanged or returning a meaningful result value.
This register clobber information currently is only for documentation purposes.
Note that the address ($ffd5 in the example above) can actually be an expression as long as it is a compile time constant. This can
make it easier to define jump tables for example, like this::