Programming MacVAX

Single Process Mode

Responsibilities of an OS

IO

MacVAX has no external peripherals other than the console. This is accessed via the console internal processor registers. IO can be perform either by polling the Ready and Done bits of the console control registers or through an interrupt service routine. MacVAX simulates asyncronous I/O on output by calculating a random interval between the initiation of output and the Interrupt for IO completion.

The console may also be written to or read from via the XFC Console IO calls. These calls provide a simpler environment for introductory courses. These calls do use the console registers so the effects of IO can be observed by the student.

Disk IO can be performed only through the XFC File I/O calls. These provide read/write access to files on the Macintosh's disk(s). It was intended to provide a more realistic disk device which would have to be accessed via a user written device driver, but this has yet to eventuate.