More flexible session trace output

[senier]

Context and Problem Statement

Debugging and validating a protocol session requires some insight into the transitions that the state machine performs. We currently have two mechanisms to achieve that: When the --debug flag is passed on the rflx generate command line, the state transitions and error output is printed to the console using Ada.Text_IO. We use this for our own tests when running on Linux. The other option is to use the Next_State function to return the next state in the main loop and print its value using the 'Image function.

Both approaches are not ideal. Ada.Text_IO may not be available for on-target debugging in embedded systems when using a limited runtime. Printing the state names from the session context only reveals those states that follow an IO state - what happens in between cannot be observed. Furthermore, using 'Image may require runtime support which may not available or desirable.

Use Cases

• Debug protocol execution on an embedded target
• Use debug output facilities other than Ada.Text_IO

Considered Options

O1

Replace the current Ada.Text_IO and Put_Line calls by a custom package RFLX_Debug with a procedure RFLX_Debug.Print (Text : String). The inclusion of the package and calls to the Print functions is governed by the presence of the --debug flag.

+ Little implementation effort
+ Simple, unified interface
+ Simple command line
− RFLX_Debug must be provided externally
− No out-of-the box use of debug functionality
− No well-defined / checked API for RFLX_Debug

O1a

Like O2, but a specification file for RFLX_Debug is generated.

+ Moderate implementation effort
+ Simple, unified interface
+ Simple command line
− RFLX_Debug body must be provided externally
− No out-of-the box use of debug functionality

O1b

Like O1, but the RFLX_Debug package with a default implementation mapping to Ada.Text_IO is generated. An optional parameter spec can be passed to the --debug switch in which case the default body would not be generated.

+ Default behavior as convenient as current behavior
+ Compatible with current solution
− More complex to implement
− May result in conflicts between custom and generated trace packages

O2

Include Ada.Text_IO and generate calls to Put_Line as before if the --debug flag is used. A new optional parameter external can be passed to --debug which includes RFLX_Debug and generates calls to Print. The spec and code for RFLX_Debug must be provided by the user.

+ Default behavior as convenient as current behavior
+ Compatible with current solution
− Slightly more complex to implement than O1
− No well-defined / checked API for RFLX_Debug

O2b

Like O2, but a specification is generated for RFLX_Debug.

+ Default behavior as convenient as current behavior
+ Compatible with current solution
− Slightly more complex to implement than O1

Decision Outcome

O2b