what is the problem.......?

2004.11.09 16:12:41 (*) Building system_ram_contents.srec using "build"

# 2004.11.09 16:12:41 (*) cd F:/kdj/adtb2_cyclone/IF_single_flash/040927_3.1IF_single_4.1 ; nios-build --sdk_directory=F:/kdj/adtb2_cyclone/IF_single_flash/040927_3.1IF_single_4.1/nios_cpu_sdk -s -o system_ram_contents.srec -b 0 nios_cpu_sdk/src/main2.c

nios_cpu_sdk/src/main2.c.o: In function `main':

nios_cpu_sdk/src/main2.c.o(.text+0xa0): undefined reference to `mytimerISR'

nios_cpu_sdk/src/main2.c.o(.text+0xa2): undefined reference to `mytimerISR'

nios_cpu_sdk/src/main2.c.o(.text+0xa4): undefined reference to `mytimerISR'

nios_cpu_sdk/src/main2.c.o(.text+0xa6): undefined reference to `mytimerISR'

# ## nios-build error: last system call returned256

# ## (Perhaps you need ".global _start" and "start:")

Died at - line 85.#

# 2004.11.09 16:12:46 mk_custom_sdk: WARNING

#

# 256 cd F:/kdj/adtb2_cyclone/IF_single_flash/040927_3.1IF_single_4.1 ; nios-build --sdk_directory=F:/kdj/adtb2_cyclone/IF_single_flash/040927_3.1IF_single_4.1/nios_cpu_sdk -s -o system_ram_contents.srec -b 0 nios_cpu_sdk/src/main2.c

#

ERROR: Could not build Peripheral Contents for nios_cpu

Error in processing. System NOT successfully generated.

mytimerISR is the function name of timer interruption.it's contained in the program.

# ## nios-build error: last system call returned256

what's the meaning??????

thx

faint boy