[U-Boot] Enabling of KGDB using U-Boot

hi I 've Cavium Networks Octeon processor with U-Boot 1.1.1 and Debian GNU/Linux 5.0 octeon I want to debug the kernel through KGDB. I compiled the kernel with KGDB configuration but when I boot the kernel on Octeon Board it boot as usual and doesnot wait for remote host to connect through serial connection. what are the configuration  for U-Boot to enable KGDB with U-boot. I 've tried these commands setenv bootargs kgdb=ttyS1,115200 but bootloader doesnot  recognize it.

Thanks.