System Control Handlers

#	Meaning	OS_ChangeEnvironment R1 value	R2 value	R3 value
0	Memory limit	Memory limit	Unused	Unused
1	Undefined instruction	Handler code	Unused	Unused
2	Prefetch abort	Handler code	Unused	Unused
3	Data abort	Handler code	Unused	Unused
4	Address exception	Handler code	Unused	Unused
5	Other exceptions (reserved)	Unused	Unused	Unused
6	Error	Handler code	Handler R0	Error buffer
7	CallBack	Handler code	Handler R12	Register dump buffer
8	BreakPoint?	Handler code	Handler R12	Register dump buffer
9	Escape	Handler code	Handler R12	Unused
10	Event?	Handler code	Handler R12	Unused
11	Exit	Handler code	Handler R12	Unused
12	Unused SWI?	Handler code	Handler R12	Unused
13	Exception registers	Register dump buffer	Unused	Unused
14	Application space	Memory limit	Unused	Unused
15	Currently active object	CAO pointer	Unused	Unused
16	UpCall	Handler code	Handler R12	Unused
32	Branch Through 0 Handler?	Handler code	Unused	Unused
33	Command Line Area?	Unused	Size of command line area	Command line area
34	Exception Dump Region	Unused	Size of exception dump region	Exception dump region

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RISC OS is an Open Source operating system owned by RISC OS Developments Ltd and licensed primarily under the Apache 2.0 license.