At the core of the firmware lies the Linux kernel, usually a heavily modified version tailored by Broadcom and subsequently customized by the original equipment manufacturer (OEM) or the Internet Service Provider (ISP). Due to resource constraints inherent in devices of this class—often limited to 16MB or 32MB of RAM—the kernel is stripped of unnecessary modules. It is optimized specifically for packet routing, Network Address Translation (NAT), and, most importantly, the control of the DSL Physical Layer (PHY).
console=ttyS0,115200 root=31:03 rootfstype=squashfs init=/sbin/init mtdparts=spi0.0:512k(cfe),256k(env),256k(config),3M(kernel),5M(rootfs) bcm63381b0 firmware
