1. Field of the Invention
The present invention relates generally to Power over Ethernet (PoE) and, more particularly, to a system and method for mirroring PoE registers in a physical layer device (PHY) over a single isolation boundary. These registers can be the actual PoE registers or a mirrored copy (virtual).
2. Introduction
PoE communication systems provide power and data communications over a common communications link. Specifically, a power source equipment (PSE) device connected to the physical layer of a first node of the communications link provides direct current (DC) power to a powered device (PD) at a second node of the communications link. The DC power is transmitted simultaneously over the same communications medium along with high-speed data.
An important aspect of a PoE device is its management system, which interfaces with the subsystems in the PoE device. One of those subsystems is the PSE subsystem, which includes a PSE controller, as well as the data subsystem that may include but is not limited to a PHY chip, switch chip, or both. The PSE controller performs such functions as discovering a presence of PD devices by checking for characteristic resistances, performing optional classification, managing/integrating power, and monitoring current draw.
The management system is often referred to as the system host. This host includes a local central processor unit (CPU) or simple microcontroller that may run some sort of firmware or software. In some cases, the CPU, PHY and switch may be embedded in one chip while in other larger systems they may be physically located on separate printed circuit boards (PCBs).
A part of the interface between the PHY and a PoE chip is an isolation boundary. A DC isolation boundary is typically formed between the PHY and the PSE controller to limit any effects of DC feedback associated with the DC voltage supply circuit. One of the most common ways of transferring signals across the isolation boundary is to use opto-isolators or opto-coupling devices. The isolation boundary is typically between the PoE subsystem and the rest of the host subsystem that needs to communicate to it. This is due to where the power is fed on the line side of the transformer as compared to the PHY side of the transformer. The isolation boundary is crossed when these subsystems need to communicate with one another. There are several options to connect the PoE subsystem to the rest of the system for communication. The connection may go to the CPU subsystem directly or to the PHY subsystem. If one were to connect each PHY with its associated PSE controller(s) directly, then separate connections would result for each “slice” of ports. These multiple slices would require multiple isolation boundaries. What is needed therefore is a mechanism that enables a single isolation boundary between the PHYs and the PSE controllers. This single isolation boundary would lower the overall system cost and enable the various slices to be treated together (i.e., a vertical look at the PoE, PHY, switch, etc. on a per port basis).