USERV
Specification
This vector is called to extend the MOS in various ways.
On entry: A=&00 OSBYTE &88 (called by *CODE) A=&01 *LINE, XY=>command line A=&02-&DF reserved A=&E0-&FF OSWORD &E0-&FF On exit: All registers can be trashed by the handler
Programming considerations
When USERV is called with A=&00 or A=&E0+ it will have been called from the OSBYTE or OSWORD handler:
- X and Y will already have been stored in the MOS register store at &F0 and &F1, so (&F0),Y addressing can be used to access the OSWORD control block. Note that if your code calls OSBYTE/OSWORD then &F0/&F1 will be overwritten.
- Interupts will be disabled, and will be restored on return from the USERV code. If your code takes a significant amount of time it must turn interupts on to allow clocks, etc. to continue.
- A will be restored on return from the USER code, so your code does not need to save and restore it.
- X and Y are undefined on return from OSWORD, so the USERV code does not need to restore them.
Extensions
Calling USERV with A=&02-&DF can be used for application-specific extensions, but should be treated as "private" to that application usage.
