RTEMS Shell User's Guide
Real-time embedded systems vary widely based upon their operational and maintenance requirements. Some of these systems provide ways for the user or developer to interact with them. This interaction could be used for operational, diagnostic, or configuration purposes. The capabilities described in this manual are those provided with RTEMS to provide a command line interface for user access. Some of these commands will be familiar as standard POSIX utilities while others are RTEMS specific or helpful in debugging and analyzing an embedded system. As a simple example of the powerful and very familiar capabilities that the RTEMS Shell provides to an application, consider the following example which hints at some of the capabilities available:
Welcome to rtems-4.8.99.0(SPARC/w/FPU/sis)
COPYRIGHT (c) 1989-2008.
On-Line Applications Research Corporation (OAR).
Login into RTEMS
login: rtems
Password:
RTEMS SHELL (Ver.1.0-FRC):/dev/console. Feb 28 2008. 'help' to list commands.
SHLL [/] $ cat /etc/passwd
root:*:0:0:root::/:/bin/sh
rtems:*:1:1:RTEMS Application::/:/bin/sh
tty:!:2:2:tty owner::/:/bin/false
SHLL [/] $ ls /dev
-rwxr-xr-x 1 rtems root 0 Jan 01 00:00 console
-rwxr-xr-x 1 root root 0 Jan 01 00:00 console_b
2 files 0 bytes occupied
SHLL [/] $ stackuse
Stack usage by thread
ID NAME LOW HIGH CURRENT AVAILABLE USED
0x09010001 IDLE 0x023d89a0 - 0x023d99af 0x023d9760 4096 608
0x0a010001 UI1 0x023d9f30 - 0x023daf3f 0x023dad18 4096 1804
0x0a010002 SHLL 0x023db4c0 - 0x023df4cf 0x023de9d0 16384 6204
0xffffffff INTR 0x023d2760 - 0x023d375f 0x00000000 4080 316
SHLL [/] $ mount -L
File systems: msdos
SHLL [/] $
In the above example, the user rtems logs into a
SPARC based RTEMS system. The first command is
cat /etc/passwd. This simple command lets us
know that this application is running the In Memory
File System (IMFS) and that the infrastructure has
provided dummy entries for /etc/passwd and a few
other files. The contents of /etc/passwd let
us know that the user could have logged in as root.
In fact, the root user has more permissions
than rtems who is not allowed to write into the
filesystem.
The second command is ls /dev which lets us
know that RTEMS has POSIX-style device nodes which
can be accesses through standard I/O function calls.
The third command executed is the RTEMS specific
stackuse which gives a report on the stack
usage of each thread in the system. Since stack
overflows are a common error in deeply embedded systems,
this is a surprising simple, yet powerful debugging aid.
Finally, the last command, mount -L hints that
RTEMS supports a variety of mountable filesystems. With
support for MS-DOS FAT on IDE/ATA and Flash devices as
well as network-based filesystens such as NFS and TFTP,
the standard free RTEMS provides a robuse infrastructure
for embedded applications.
This manual describes the RTEMS Shell and its command set.
In our terminology, the Shell is just a loop reading user
input and turning that input into commands with argument.
The Shell provided with RTEMS is a simple command reading
loop with limited scripting capabilities. It can be connected
to via a standard serial port or connected to the RTEMS
telnetd server for use across a network.
Each command in the command set is implemented as a single subroutine which has a main-style prototype. The commands interpret their arguments and operate upon stdin, stdout, and stderr by default. This allows each command to be invoked independent of the shell.
The described separation of shell from commands from communications mechanism was an important design goal. At one level, the RTEMS Shell is a complete shell environment providing access to multiple POSIX compliant filesystems and TCP/IP stack. The subset of capabilities available is easy to configure and the standard Shell can be logged into from either a serial port or via telnet. But at another level, the Shell is a large set of components which can be integrated into the user's developed command interpreter. In either case, it is trivial to add custom commands to the command set available.
RTEMS Shell User's Guide
Copyright © 1988-2008 OAR Corporation