6.7. Exception Handling System

M1750 Ada supports exception declarations, the raise statement, and exception handlers. It does not support exception propagation. We expect M1750 Ada application programs to regard an exception as a fatal error, and to log the context of the failure (in non-volatile RAM for example), then to restart the program.

There is no overhead associated with calling or entering a subprogram in which an exception is declared, other than the space required to hold the exception descriptor. This a small record that contains the name of the exception (as a string), and several other items required to satisfy the needs of the predefined package Ada.Exceptions.

An exception may also be raised by a call of Ada.Exceptions.Raise_Exception. The advantage of making the call rather than using the raise statement is that the call may attach a message to the exception.

Unhandled exceptions, hardware faults and deadline errors are reported within the run-time system, and can be handled as interrupts. The default action is to log the fault (via application-dependent code), then do a warm restart.