The Tornado shell, WindSh, allows you to download application modules, and to invoke both VxWorks and application module subroutines. This facility has many uses: interactive exploration of the VxWorks operating system, prototyping, interactive development, and testing.

WindSh can interpret most C language expressions; it can execute most C operators and resolve symbolic data references and subroutine invocations. You can also interact with the shell through a Tcl interpreter, which provides a full set of control structures and lower-level access to target facilities. For a more detailed explanation of the Tcl interface, see 5.7 Tcl: Shell Interpretation.

WindSh executes on the development host, not the target, but it allows you to spawn tasks, to read from or write to target devices, and to exert full control of the target.¹ Because the shell executes on the host system, you can use it with minimal intrusion on target resources. As with other Tornado tools, only the target agent is required on the target system. Thus, the shell can remain always available; you can use it to maintain a production system if appropriate as well as for experimentation and testing during development.

Shell operation involves three components of the Tornado system, as shown in Figure 5-1.

• The shell is where you directly exercise control; it receives your commands and executes them locally on the host, dispatching requests to the target server for any action involving the symbol table or target-resident programs or data.

• The target server manages the symbol table and handles all communications with the remote target, dispatching function calls and sending their results back as needed. (The symbol table itself resides entirely on the host, although the addresses it contains refer to the target system.)

• The target agent is the only component that runs on the target; it is a minimal monitor program that mediates access to target memory and other facilities.

  Figure 5-1:  Tornado and the Shell

  

The shell has a dual role:

• It acts as a command interpreter that provides access to all VxWorks facilities by allowing you to call any VxWorks routine.

• It can be used as a prototyping and debugging tool for the application developer. You can run application modules interactively by calling any application routine. The shell provides notification of any hardware exceptions. See System Modification and Debugging, for information about downloading application modules.

The capabilities of WindSh include the following:

• task-specific breakpoints

• task-specific single-stepping

• symbolic disassembler

• task and system information utilities

• ability to call user routines

• ability to create and examine variables symbolically

• ability to examine and modify memory

• exception trapping

1:  A target-resident version of the shell is also available; for more information, see VxWorks Programmer's Guide: Target Shell.