User's Manual

ADVANCED TOPICS
Table
11-1. NPX Context Switching
Step Operation
Lines
(Figure
11-3)
1. Save the working registers
28,29
2. Set up address for kernel work area
30,31
3. Get current task
10 from Task Register
32
4.
Clear Task Switch flag to allow NPX work
34
5. Inhibit interrupts
35
6. Compare owner with current task 10
37
If same owner:
7a. Restore working registers
48,49
7b.
and return
50
If
owner is not
current task:
8a. Use owner 10 to save old context in Its TSS 42,43,44
8b. R,estore context of current task;
45
restore working registers;
46
and return 52
updated by a re-entrant procedure that is invoked by an inter-processor interrupt. The handler must
ensure that the segment registers, the LDTR and the TR, are re-loaded. This happens automatically if
the interrupt
is serviced by a task switch.
11.6 SHUTDOWN
Shutdown occurs when a severe error condition prevents further processing. Shutdown is very similar
to
HL T in that the 80286 stops executing instructions. The 80286 externally signals shutdown as a
Halt bus cycle with
Al =0. The NMI or RESET input will force the 80286 out of shutdown. The
INTR input is ignored during shutdown.
11-7