Browse Prior Art Database

Enhanced Multi-mode Serial Support

IP.com Disclosure Number: IPCOM000019257D
Original Publication Date: 2003-Sep-08
Included in the Prior Art Database: 2003-Sep-08
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Abstract

In addition to the normal environmental management functions the baseboard management controller (BMC) design for the server requires supporting serial over a Local Area Network as well as local terminal emulation or Emergency Management Protocol (EMP). In addition to these functions, Linux requires a terminal emulation program to be attached locally so the users can run a remote application using a terminal server. These installations require the terminal server emulation mode of operation where the Linux text is directed to either a serial port or over the LAN to a proxy application somewhere in the network. The following design provides a combination of functions depending on the customer requirements for the operating system. The serial interface design provides the normal serial port function. The circuitry also provides an interface into the BMC for monitoring and controlling the environmental conditions of the server, a remote serial connection over (LAN), and a terminal emulation function in conjuction with the BMC function for concurrent Linux operation and environmental control.

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Enhanced Multi-mode Serial Support

      The high level diagram below depicts this functionality. This function is available regardless of the power or operational state of the server since all critical components are powered with the auxiliary voltage. In the simplistic design flow three switches allow the user to monitor normal serial traffic, allow the BMC to break-in and communicate with the user, and allow system serial communication to the BMC concurrently with the normal serial communication. This feature is key in the Linux environment.

Vaux

I2C

    To provide the normal serial redirection, switch X1 is activated with the other switches deactivated. To monitor the traffic from COM1 to the RS-232 interface, the BMC software activates switch X2. The BMC can then monitor the serial activity for special key sequences. Once these key sequences are detected, the BMC can then deactivate switch X1 and continue communication over the external serial interface. Activating switch X2 also allows the BMC to packetize the serial data and provide the 2serial over LAN connectivity using the IC bus between the BMC and the system Ethernet chip. Activating switches X1 and X3 and deactivation switch X2 allows concurrent operation of the normal serial traffic (COM1-to-RS-232) and allows the BIOS to communicate with a remote user using the BMC (COM2-to-BMC and Ethernet).

    The truth table in the diagram depicts the state of the control signals to route data among the different entities. In all these switching scenarios, the control signals must ensure the non-disruptive switch-over among all three interfaces. This is accomplished with tri-state drivers and overlapping enable and disable signals.

BMC

Ethernet

Com 2

X3

X2

Com 1

X1

RS-232

1

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-Enable COM2 to BMC/System

EN_C...