hi @nsherin , I succeed pxe boot with ubuntu 18.04 using following:
kernel tftp://192.168.84.16/os/ubuntu/Desk18.04/vmlinuz
initrd tftp://192.168.84.16/os/ubuntu/Desk18.04/initrd.lz
imgargs vmlinuz initrd=initrd.lz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.84.16:/images/os/ubuntu/Desk18.04/ ip=dhcp systemd.mask=tmp.mount rw -- || read void
boot || goto MENU