Intermec ck1 Reference Guide
Appendix A —
µClinux System
CK1 SDK Programmer’s Reference Manual
297
area with other processes, and synchronize itself with other processes.
Linux supports a number of IPC mechanisms such as pipes and signals,
but it also supports many of the Unix System V IPC mechanisms.
Linux supports a number of IPC mechanisms such as pipes and signals,
but it also supports many of the Unix System V IPC mechanisms.
A signal is a very short message allowing the process to communicate the
occurrence of asynchronous events to other process. It is the oldest inter
process communication method used by Unix systems. A signal could be
generated by a software or hardware interrupt or by some error condition,
for example, a process attempting to access an invalid location in its virtual
memory. Linux includes a set of defined signals with a prefix of signal that
the kernel can generate or that can be generated by other processes with
correct privileges in the system. A set of system calls are also introduced by
the Linux kernel, which allow programmers to send and determine how
the signal should be handled. The options for the process to handle the
signal are to block the signals or either choose to handle themselves or
allow the kernel to handle them with a default action. The process is also
in some cases allowed to ignore the signal.
occurrence of asynchronous events to other process. It is the oldest inter
process communication method used by Unix systems. A signal could be
generated by a software or hardware interrupt or by some error condition,
for example, a process attempting to access an invalid location in its virtual
memory. Linux includes a set of defined signals with a prefix of signal that
the kernel can generate or that can be generated by other processes with
correct privileges in the system. A set of system calls are also introduced by
the Linux kernel, which allow programmers to send and determine how
the signal should be handled. The options for the process to handle the
signal are to block the signals or either choose to handle themselves or
allow the kernel to handle them with a default action. The process is also
in some cases allowed to ignore the signal.
When sending a signal to another process, the kernel updates the
descriptor of the destination process, which reads it when it enters to
running stage. The process running can also choose to wait for a signal by
entering Suspend mode until the received signal raises an interrupt and
wakes it up. The signal sending has also some restrictions where the
normal process can only be sent to a process with a same uid and gid or to
processes in the same process group. Of course the kernel and the super
user are capable of sending signals to every other process.
descriptor of the destination process, which reads it when it enters to
running stage. The process running can also choose to wait for a signal by
entering Suspend mode until the received signal raises an interrupt and
wakes it up. The signal sending has also some restrictions where the
normal process can only be sent to a process with a same uid and gid or to
processes in the same process group. Of course the kernel and the super
user are capable of sending signals to every other process.
As signals are only capable of transferring information that was limited to a
single number, pipes allow more useful data to be exchanged between the
processes. The term pipe is used to describe the connection where the
information flow can be done between the processes. A command shell
pipe can easily be done with a | separator.
single number, pipes allow more useful data to be exchanged between the
processes. The term pipe is used to describe the connection where the
information flow can be done between the processes. A command shell
pipe can easily be done with a | separator.
ls | lpr
This previous command line pipes the output from the ls command listing
into the standard input of the lpr command, which prints the results on
the default printer. Basically, the idea with pipe command implementation
is that both data structures point at the same temporary virtual file system
inode, which is assigned to points at a physical page in memory. As the ls
writes to the pipe, bytes are copied into the shared data page and the lpr
copies these bytes again from the same shared data page.
into the standard input of the lpr command, which prints the results on
the default printer. Basically, the idea with pipe command implementation
is that both data structures point at the same temporary virtual file system
inode, which is assigned to points at a physical page in memory. As the ls
writes to the pipe, bytes are copied into the shared data page and the lpr
copies these bytes again from the same shared data page.
System V IPC
The System V IPC mechanisms provide forms of IPC facilities originally
introduced by Columbus Unix variant but later adopted by AT&T. The
System V IPC provides tools for performing reliable, system-wide
communication. It supports the three kinds of different mechanisms:
message queues, semaphores, and shared memory, which are all
implemented via the kernel system call. The user mode process can access
these system calls by passing a unique identifier to the resource, which is
introduced by Columbus Unix variant but later adopted by AT&T. The
System V IPC provides tools for performing reliable, system-wide
communication. It supports the three kinds of different mechanisms:
message queues, semaphores, and shared memory, which are all
implemented via the kernel system call. The user mode process can access
these system calls by passing a unique identifier to the resource, which is