Debugging Support

When ACT programs get long, it may be difficult to track down why a particular circuit is not being constructed properly. To help debug this, there are two basic debugging constructs provided.

Sometimes it is useful to be able to check that a parameter (or an expression of parameters) has a reasonable value. To express this, ACT supports explicit assertions. We use Hoare's syntax for assertions, so the assertion that x must be 8 would be written

{x=8};

If a more meaningful message is required, the following syntax is also supported:

{x=8 : "This assertion failed"};

which also reports the message specified when the assertion failed.

During circuit development/debugging, it may be helpful to assert that two signals are connected to each other or in fact disconnected from each other at a particular point during circuit construction. To assert that a is connected to b, use:

bool a;
bool b;
 
{ a !== b : "a and b are connected connected!" };  // this will pass
a = b;
{ a === b : "a and b are not connected!" }; // this will pass
{ a !== b : "a and b are connected connected!" };  // this will fail

The operators === and !== are used to check that the two signals are connected or disconnected at the point the assertion was encountered during circuit construction.

ACT supports debug log messages in verbose mode. A debug log statement can be written as:

...
${ "Hello!" };   // log message "Hello"
...

When this construct is encountered, a log message is displayed. By default these messages are ignored; to see them, use the -Vconfig ACT command-line option to any ACT tool. (Note that this will also display the names of the configuration files loaded by ACT.)

A log message can include multiple values, including parameter expressions. This can be useful to check values of parameters.

${ "Parameter i has value ", i };  // display the value of i