GeneveOS Device Operation

Accessing devices (floppy disk, hard disk, serial connector, printer) is possible in GeneveOS via XOP calls.

User-task XOPs

User-task XOPs are available for use in application programs. Here is a typical example:

PABADD EQU  >F180   
FILE   DATA 8
...
       LI   R0,PABADD
       XOP  @FILE,0
       MOVB @PABADD+2,R0
       JNE  ERROR
       ...

Similar as with the TI-99/4A device service routine concept (DSR), a Peripheral Access Block (PAB) must be set up prior to invoking the XOP.

Device Service Routine Call

	Input	Output
R0	Pointer to PAB	-

The actual operation is contained in the Peripheral Access Block (PAB).

Peripheral Access Block

While the TI-99/4A DSRs expect the PAB to be stored in VDP RAM, the Geneve OS DSRs use CPU RAM for the PAB, which means the PAB need not be copied to the video RAM before use. Also, you can choose to have the I/O buffers in VDP or CPU RAM.

The general layout of the PAB is as follows:

00	01	02	03	04	05	06	07	08	09	0A	0B	0C	0D	0E	0F	10 ...
Opcode	Mode	Error code	Buffer address			Record number		Record length		Memory type	Character count			Status byte	Name length	Name