Download - Academy Publisher

1) Process context storage areas. It is used to store
process contexts before present subsystem is interrupted.
There are two process context storage areas, which are
separately used to store the local subsystem’s contexts
and the network subsystem’s contexts. Certainly, they
have different starting address.
2) Switch back registers. It is used to store address of
the next instruction that present sub-system is going to
execute at the time of being interrupted. There are also
two registers in order to store two sub-systems’ address of
the next instruction separately.
In the next, systemic design of switch mechanism is
elaborated. And then, system-switch flows of booting
and running stages of operating system are illustrated.
III. DESIGN OF SYSTEM-SWITCH MECHANISM
In order to implement the system-switch between two
sub-systems, a system-switch mechanism is designed.
Firstly, as it has two sub-buses and they are both
connected to the shared bus according to the bridge,
some values can be assigned to the bus-bridge controller
register to realize connection with different sub-systems.
Secondly, as mentioned above, process contexts should
be conserved for the sake that sub-systems could run
from the breakpoint. And in our mechanism, clock
interrupt processor is chosen as the breakpoint of
system-switch in order to make system switch in time [5] .
Thirdly, one piece of space in instruction cache is opened
up to conserve the switch-flag. The switch-flag is a
variable which is used to point out whether system need
to be switched or which switch direction should be
adopted. Both of local sub-system and network
sub-system can visit it and change its value. Besides,
switch command is designed so that users can control
system-switch through command. Specific design is
shown as follows:
1) Trigger of system-switch.
System switch mechanism adopts command as the
trigger. Users control systems’ switch through inputting
some commands. After users input switch commands, a
process called switch process will be created. This
process will set the switch flag according to the
parameters of switch command.
2) Entrance of system-switch.
As clock interrupt occurs periodically, it is chosen as
the breakpoint. In our mechanism, clock processor is
modified. Some procedures are added into it which are
used to judge switch flag and then determine whether
system should be switched and which direction should be
changed to.
3) The core switch program.
The core switch program is called bus-switch program,
and it is core module to realize bus switch. Bus-switch
program is located in the instruction cache. And
apparently it has two parts which are used in the different
directions of system switch: local-network bus-switch
program and network-local bus-switch program [6] . They
are stored in different starting addresses of instruction
cache. In this bus-switch program, some functions are
implemented as follows:
a) Store clock interrupt processor’s context of
present sub-system to its process context storage area,
such as the data segment, relevant registers, stack and so
on.
b) Assign specific values to bus bridge controller
register to make shared bus connect to target
sub-system’s bus.
c) Restore the values of target sub-system’s process
context storage area to the relevant registers, stack and so
on. And then, PC register is assigned as the value of
target sub-system’s switch back register.
4) Exit of system-switch.
After system bus is switched and the context and PC
are restored, the system enters into target sub-system’s
Figure 2. Flow chart of system-switch
Figure 3. Flow chart of system-switch command
clock interrupt processor and goes on running from the
breakpoint. Figure2 is the flow chart of system-switch.
235