Browse Prior Art Database

Method to Provide Multi-master Support to the Primary Side of the IBM I2C MUX

IP.com Disclosure Number: IPCOM000015036D
Original Publication Date: 2002-May-08
Included in the Prior Art Database: 2003-Jun-20
Document File: 1 page(s) / 40K

Publishing Venue

IBM

Abstract

The current implementation of the IBM I2C MUX lacks a mechanism to allow multiple I2C master to access the devices behind the MUX. One can not simply rely on I2C master arbitration to meter access to the MUX. Since an I2C master may be talking to a devices that requires multiple separate I2C transactions to complete a task, another master changing the MUX direction in the middle of these multiple transactions would be catastrophic. The MUX must employ a mechanism to "lock" the direction of the MUX until the current master is finished with the transaction "group." This invention will add features to the IBM I2C MUX that will allow masters to gain exclusive access to the MUX.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 51% of the total text.

Page 1 of 1

Method to Provide Multi-master Support to the Primary Side of the IBM I2C MUX

The current implementation of the IBM I2C MUX lacks a mechanism to allow multiple I2C master to access the devices behind the MUX. One can not simply rely on I2C master arbitration to meter access to the MUX. Since an I2C master may be talking to a devices that requires multiple separate I2C transactions to complete a task, another master changing the MUX direction in the middle of these multiple transactions would be catastrophic. The MUX must employ a mechanism to "lock" the direction of the MUX until the current master is finished with the transaction "group." This invention will add features to the IBM I2C MUX that will allow masters to gain exclusive access to the MUX.

The invention consists of a multiplexer, logic to implement the MUTEX locking, logic to implement the bus switching and logic to interface to the I2C bus.

The invention is built such that an I2C master can read and write data to the device using the standard Philips I2C protocol. To the I2C masters the invention looks like a standard I2C based memory device. The invention can support as few as one master and is only limited in size by the number of secondary I2C busses and number of I2C masters that require access to the MUX. Each I2C master is assigned a semaphore bit in the invention with the highest priority master owning the MSB and other masters following from there. No two I2C masters can share a bit. Each I2C master is assigned a different bit since by the I2C arbitration rules two different I2C masters can successfully write the same data to a device during the exact same I2C bus transaction. If a single bit were to be used, two I2C master could presume that they each have exclusive access. In addition to the I2C semaphore bits, the MUX select bits are assigned beginning with the LSB. Allocation of the semaphore and MUX select bits must not overlap. The system designer can choose how alloca...