h6. [[OS SWI Calls]] h6(. » OS_CallBack h2. OS_CallBack h5. (SWI &15) |_<^{width:3em}. Entry | | |<^. R0 |<^. Address of the register save block, 0 to read | |<^. R1|<^. Address of the callback handler, 0 to read | |_<^{width:3em}. Exit | | |<^. R0|<^. Address of previous register save block | |<^. R1|<^. Address of previous callback handler | h4. Use OS_CallBack sets up the address of the [[CallBack Handler|CallBack handler]] and its register save block. h4. Notes The register save block must be word-aligned and 16 words long. This call is deprecated and should not be used. Please use [[OS_ChangeEnvironment]] instead. Internally, this SWI just calls OS_ChangeEnvironment This sets up the address of the CallBack handler and the register save block, zero for either value meaning no change - hence you can read the current value. Once a CallBack handler has been installed, you can request callbacks via [[OS_SetCallBack]]. For information on callbacks refer to [[CallBack Handler]]. h4. See also * [[OS_SetCallBack]] * [[OS_ChangeEnvironment]]