How to use KGDB

My setup

one beaglebone black
one usb to serial cable connected on proper uart header
properly compiled kernel , vmlinux, uImage, uboot.bin, MLO, device tree binary
booting through uSD card

beaglebone_defconfig added these lines


I don’t know how this script works, but I used this
uenv.txt =
netargs=setenv bootargs console=ttyO0,115200n8 console=tty0 root=/dev/mmcblk0p2 ro rootfstype=ext4 kdgb=ttyO0,115200N8 kgdboc=ttyO0,115200N8 kgdbwait
netboot=echo Booting from Network …; setenv autoload no ; load mmc 0:1 ${loadaddr} uImage ; load mmc 0:1 ${fdtaddr} am335x-boneblack.dtb ; run netargs ; bootm ${loadaddr} - ${fdtaddr}
uenvcmd=run netboot

last few lines of boot

io scheduler deadline registered
[ 0.165060] io scheduler cfq registered (default)
[ 0.166024] tps65217-bl tps65217-bl: no platform data provided
[ 0.166064] tps65217-bl: probe of tps65217-bl failed with error -22
[ 0.166763] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
[ 0.168197] omap_uart 44e09000.serial: did not get pins for uart0 error: -19
[ 0.168491] 44e09000.serial: ttyO0 at MMIO 0x44e09000 (irq = 88) is a OMAP UART0
[ 0.899496] console [ttyO0] enabled
[ 0.903620] kgdb: Registered I/O driver kgdboc.
[ 0.908399] kgdb: Waiting for connection from remote gdb…
[ 0.914252] Internal error: Oops - undefined instruction: 0 [#1] SMP THUMB2

Entering kdb (current=0xdf04eac0, pid 1) on processor 0 due to Keyboard Entry

and just nothing.
What I have to do to run control this usb to uart interface over kgdb?