=> R0-R9 = as required for target SWI
R10 = target SWI number
<= dependent on SWI called
This SWI allows a target SWI number to be determined at run time, and passed in a register. This removes the need for a common idiom of dynamic code, in language library SWI veneers for example. In an APCS-R library, use OS_CallASWIR12.
Note that OS_CallASWI is merely an alias for calling the target SWI. It has no entry/exit conditions of its own, except for the special use of R10. To call a target SWI with X bit set, use the X form of the SWI number in R10; there is no distinction between OS_CallASWI and XOS_CallASWI.
You cannot call OS_CallASWI or OS_CallASWIR12 via OS_CallASWI, since there is no defined final target SWI in this case.
You cannot usefully call OS_BreakPt or OS_CallAVector using OS_CallASWI, as OS_CallASWI will corrupt the processor flags before entering the target SWI.
For future compatibility, you should always use this SWI in preference to any local construction for calling a SWI by number. For compatibility with older versions of RISC OS, a new CallASWI module will be made available.
Note that this SWI calling mechanism is almost certainly faster than any other alternative implementation, including the original _kernel_swi and _swix code contained in older versions of the SharedCLibrary. The new SharedCLibrary now simply uses OS_CallASWIR12 for _kernel_swi and _swix.
OS_CallASWI cannot be called from BASIC as BASIC only passes registers R0-R7 via its SYS instruction. It would not be useful anyway.
Provided by RISC OS 3.70+, and also the CallASWI module for earlier versions of RISC OS.
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