This is the I/O Function Dispatcher for a File. It is called from within the system library with BX containing the offset to the function we are calling.
| BX | Function | Description |
|---|---|---|
| 0010 | OpenFunc | Pointer to I/O routine that opens this file |
| 0014 | InOutFunc | Pointer to I/O routine that performs read/write on this file |
| 0018 | FlushFunc | Pointer to I/O routine that flushes the buffer |
| 001C | CloseFunc | Pointer to I/O routine that closes this file |
These offsets are the are actually offsets to File record.
SYS03FA: PUSH ES
SYS03FB: PUSH DI
Save ES:DI on the stack.
SYS03FC: PUSH ES
SYS03FD: PUSH DI
Pass pointer to File in ES:DI to the function.
SYS03FE: ES:
SYS03FF: CALL FAR [BX+DI]
Make a far pointer to the function determined by ES:[DI+BX] (see table above).
SYS0401: OR AX,AX
Check if the I/O functions generated an error code in AX.
SYS0403: JZ 0408
Return to caller immediately if there were no errors.
SYS0405: MOV [InOutRes],AX
Record the error code in InOutRes.
SYS0408: POP DI
SYS0409: POP ES
Upon returning from the I/O functions, the parameters passed to it, i.e. ES:DI were popped-off from the stack. At this point, after restoring ES:DI, the stack is already balanced.
SYS040A: RET
Return to caller. Because it returns with a NEAR RET, it can only be called from within the system library.
See also: SYS:0499 Open Function, SYS:0480 Close Function, SYS:040B Read Function, SYS:0460 Write Function, SYS:043B Write to File Function or go back