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A. design of system-switch command
When system-switch command is executed, shell will
automatically establish system-switch process. This
process is used to set the switch-flag according to
parameters of system-switch command. Besides, in order
to prevent switch-flag from being changed unexpectedly
when next clock interrupt comes, interrupts should be
disabled during system-switch process is executed. After
switch-flag is set successfully, interrupts will be enabled
again [7] . At last, system-switch process exits. Flow chart
of system-switch command is shown in Figure3.
In order to accomplish the system-switches in
different situations, system-switch command is designed
to have different parameters. And system-switch process
can refer to these parameters to set switch-flag.
System-switch command is called BusSwitch.
Parameters of BusSwitch, its parameters’ meaning and
value of relevant switch flags are shown in table 1.
TABLE 1.
BusSwitch’ parameters and values of relevant switch-flag
BusSwitch –p command values of switch-flag
Parameter’s
Local Network
Meaning of the parameters
value (-p)
subsystem subsystem
Stop system-switch, CPU
n
0 0
works at present sub-area.
u
c
System-switch under users’
control
System-switch during data
transmitting
3 3
1 2
B. clock interrupt processor
The clock interrupt processor is the entrance and exit
of system-switch and the controller. So it is the core of
system-switch mechanism. Some procedures are added
to the clock interrupt processor to judge the switch-flag.
Then every time clock interrupt comes, clock interrupt
processor firstly does some conventional processing,
secondly judges switch-flag and then decides what kind
of actions should be adopted [8] . The process flow of
local-subsystem’s clock interrupt processor is shown in
Figure4 (The flow in the braces is the process flow of
network-subsystem’s clock interrupt processor):
IV.
SYSTEM-SWITCH FLOW ANALYSIS IN DIFFERENT
STAGES
System-switch occurs both at the stage of system
booting and system running. Absolutely, there are some
differences between two stages.
A. system-switch flow in booting stage
At this stage, we firstly start local-subsystem in order
to assure the system’s safety. Local-subsystem’s
bootloader and kernel are located in flash of local
sub-area. System begins to run from the first address of
local sub-area’s flash automatically. And system-switch
occurs when we need to operate network sub-area. In
order to assure that system will continue running from
the bootloader of network subsystem after system switch,
bootloader of local subsystem should do some extra jobs
except its normal guidance and load:
1) Initialize all the devices mounted on the shared bus,
load two system-switch programs to instruction cache.
2) Initialize process context storage area of both
subsystems as zeros.
3) Assign network sub-system’s switch back register
as the first address of network subsystem’s bootloader.
According to system-switch mechanism, users can
input the command “BusSwitch -u” to boot network
sub-area and operate it.
B. system-switch flow in running stage
There are two system-switch situations during the
running stage of operating system: user-control switch
and data-transfer switch. User-control switch means that
system-switch occurs when the users want to switch to
the other subsystem and data-transfer switch means that
the system is switched automatically when there are
some data need to be transmitted to the other subsystem.
In this situation, switch between two subsystems are
automatically proceeding until data transmission is done.
At last, target subsystem goes on running.
According to system mechanism, users can input
command “BusSwitch -u” to realize user-control switch
while input “BusSwitch –c” to realize data-transfer
switch. In situation of data-transfer switch, if local
subsystem is running now, system-switch flag is set as 1.
When next clock interrupt comes, clock interrupt
processor finds switch-flag is 1, and then it sets
switch-flag as 2 according to Figure4. Next, it goes on
processing local subsystem’s tasks. When next clock
interrupt comes, system is switched as it judges that
switch-flag is 2. After network subsystem starts to run,
interrupt return occurs and tasks of network subsystem
are executed. In next clock interrupt, it judges
switch-flag as 2, and then set it as 1. Tasks of network
subsystem are executed again, that is receiving the data.
Router process [9] judges whether data transfer has done,
if yes, switch-flag is set as 0, and if no, nothing will done.
When next clock interrupt comes, switch-flag is judged
again, if it is 1, system-switch occurs, if it is 0, system
stays at present subsystem.
Figure 4. Flow of clock interrupt processor
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