How to definition"SYSTEM_BUS_WIDTH"?

PS: The message as following:

NiosQ@localhost ~/NiosQ_program $ nios2-linux-uclibc-gcc hello_altera_avalon_pwm.c

-o hello_altera_avalon_pwm -elf2flt

hello_altera_avalon_pwm.c: In function `main':

hello_altera_avalon_pwm.c:42: error: `SYSTEM_BUS_WIDTH' undeclared (first use in

this function)

hello_altera_avalon_pwm.c:42: error: (Each undeclared identifier is reported onl

y once

hello_altera_avalon_pwm.c:42: error: for each function it appears in.)

hello_altera_avalon_pwm.c: In function `print_error':

hello_altera_avalon_pwm.c:86: error: `SYSTEM_BUS_WIDTH' undeclared (first use in

this function)

NiosQ@localhost ~/NiosQ_program $