The __interrupt keyword is a synonym for interrupt, which is allowed when using the "-ansi off" compiler option.
Use the non-standard interrupt keyword like any other type qualifier. The keyword specifies a function as an interrupt routine. It is followed by a number specifying the entry in the interrupt vector that contains the address of the interrupt routine
interrupt void f(); // OK // set the entry number in the prm-file interrupt 2 int g(); // The 2nd entry (number 2) gets the address of func g().