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BCM33xx
The BCM33xx chipset, sometimes also referred to as BCM933xx, is a cable modem SoC. An overview of the different SoCs can be found on deviwiki.
The chipsets can be divided into 3 different categories, depending on their CPUs.
BCM3382 and older
These use a single core big-endian MIPS processor. The CM firmware is based on eCos.
BCM338x and BCM3384
The SoC includes two big-endian MIPS processors, sharing the same RAM space.
- "Viper" (arch
bmips4350) - "Zephyr" (arch
bmips5000), aka "application processor"
Communication between both processors is handled by various IPC mechanisms.
The boot processor is Viper, which also runs the CM firmware (based on eCos). Once the CM system has been intialized, it may boot Linux on the "application processor".
On these platforms, Linux is only used for providing things such as sharing attached USB drives via Samba. All cable network and Wi-Fi related aspects (including the web interface) are handled by the eCos firmware - the Linux part isn't needed for the device to work as a basic modem/router.
Communication between both processors is handled by various IPC mechanisms.
BCM3390
This SoC includes two processors of differing endianness.
- ARM, "Brahma B15", (dual core, ARMv7, Cortex-A15), little-endian
- MIPS, big-endian
RAM is shared between both processors, but the MIPS core can only access part of it.
The boot processor is the ARM core. The device can be set to secure boot mode using OTP (one-time programmable) memory.
The bootloader eventually boots Linux, which in turn starts a service that loads the CM firmware into RAM, and boots the MIPS processor.
Linux handles networking, Wi-Fi, and also hosts the web interface. The CM firmware (still based on eCos) only handles access to the cable network and telephony.
Communication between both cores is handled by IPC mechanisms and virtual network interfaces.