work on interrupts

src/interrupts.s

@@ -586,9 +586,36 @@ cop_get_working_directory:
 cop_set_working_directory:
 	cop_rti
 
+
+; -----------------------------------------------------------------------------
+; Function 21: Execute User program
+;
+; Given an open file handle, load the file into memory as a PGZ-format binary,
+; and branch to its entry point. The user program will replace any user program
+; already loaded and running, and will inherit the current environment and
+; file handles. This function is used by the shell, which suspends itself and
+; waits for the exit system call to pick up with the exit code of the user
+; program.
+;
+; Arguments:
+;		A: File handle
+; Return Value:
+;		A: Error code
+
 cop_exec:
 	cop_rti
 
+; -----------------------------------------------------------------------------
+; Function 22: Exit user program
+;
+; If there is a user program running, it will be terminated, and the kernel will
+; return to the shell. The calling program provides a 16-bit exit code, which will
+; be passed back to the shell.
+;
+; Arguments:
+;		C: Exit status
+; Return Value: None
+
 cop_exit:
 	cop_rti