how to debug plsql blok

by using SQLERRM we can debug like below


EXCEPTION
                WHEN OTHERS THEN
                           FND_FILE.PUT_LINE (FND_FILE.LOG, 'Error in XXATU_BLACKLINE_EXTRACT');
                           v_error := SUBSTR(SQLERRM,1,240);
                           FND_FILE.PUT_LINE (FND_FILE.LOG, v_error);