Method and apparatus for constructing wired-AND bus systems

Abstract

A large multimaster I 2 C bus system is partitioned into smaller bus segments. The bus segments are connected by bridges that isolate the segments and direct selected transactions and commands between the segments. By programming address bitmaps that are internal to each bridge, transactions can pass through the bridges so that the various bus segments appear to be one logical bus. Because each bridge implements address filtering so that transactions are selectively forwarded from one side of the bridge to the other based on the contents of an internal address bitmap, I 2 C slave addresses can be arbitrarily populated on either side of the bridge. Duplicate I 2 C slave addresses can be also used on different segments of a single logical I 2 C bus system. Masters on one segment can reach devices connected to the same bus segment and can also reach devices with duplicate addresses on other bus segments by using a tunnel command addressed to a bridge.

What is claimed is:  
     
         1 . A method for constructing a wired-AND bus system, comprising: 
 (a) constructing a plurality of wired-AND bus segments, each bus segment having being small enough to avoid rise time problems;    (b) connecting pairs of bus segments together with bus bridges wherein each bus bridge selectively forwards transactions and commands from one bus segment to another; and    (c) connecting master devices and slave devices to the bus segments.    
     
     
         2 . The method of  claim 1  wherein each bridge comprises an address bitmap and wherein the bridge selectively forwards transactions based on information in the address bitmap.  
     
     
         3 . The method of  claim 1  wherein each bridge comprises a pair of range registers wherein values in the range registers determine which commands will be forwarded by the bridge.  
     
     
         4 . The method of  claim 1  wherein step (b) comprises connecting the bus segments into a tree hierarchy.  
     
     
         5 . The method of  claim 1  further comprising: 
 (d) programming one bus master to enter information into the address bitmaps and range registers of each bridge.  
 
     
     
         6 . The method of  claim 5  wherein the bus segments are connected into a tree hierarchy having a root level and the method comprises: 
 (e) locating the one bus master at the root level.  
 
     
     
         7 . The method of  claim 1  wherein at least some of the bridges are bidirectional bridges.  
     
     
         8 . The method of  claim 7  wherein each bidirectional bridge is comprised of two unidirectional bridges, each having a bridge ID.  
     
     
         9 . The method of  claim 8  wherein each unidirectional bridge has a different bridge ID.  
     
     
         10 . The method of  claim 1  wherein at least two slave devices have the same address and the method further comprises: 
 (f) sending a tunnel command from a bus master, the tunnel command containing data and a slave device address, to one of the bridges whereupon the bridge forwards the data to the slave device address.  
 
     
     
         11 . Apparatus for constructing a wired-AND bus system, comprising: 
 a plurality of wired-AND bus segments, each bus segment having being small enough to avoid rise time problems;    bus bridges connecting pairs of bus segments together wherein each bus bridge selectively forwards transactions and commands from one bus segment to another; and    at least one master device and at least one slave device connected to the bus segments.    
     
     
         12 . The apparatus of  claim 11  wherein each bridge comprises an address bitmap and wherein the bridge selectively forwards transactions based on information in the address bitmap.  
     
     
         13 . The apparatus of  claim 11  wherein each bridge comprises a pair of range registers wherein values in the range registers determine which commands will be forwarded by the bridge.  
     
     
         14 . The apparatus of  claim 11  wherein the bus bridges connect the bus segments into a tree hierarchy.  
     
     
         15 . The apparatus of  claim 11  further comprising a configuration host that enters information into the address bitmaps and range registers of each bridge.  
     
     
         16 . The apparatus of  claim 15  wherein the bus segments are connected into a tree hierarchy having a root level and the configuration host is located at the root level.  
     
     
         17 . The apparatus of  claim 11  wherein at least some of the bridges are bidirectional bridges.  
     
     
         18 . The apparatus of  claim 17  wherein each bidirectional bridge is comprised of two unidirectional bridges, each having a bridge ID.  
     
     
         19 . The apparatus of  claim 18  wherein each unidirectional bridge has a different bridge ID.  
     
     
         20 . The apparatus of  claim 11  wherein at least two slave devices have the same address and the apparatus further comprises a bus master that sends a tunnel command containing data and a slave device address to one of the bridges whereupon the bridge forwards the data to the slave device address.