Patent ID: 6484237
Filing Date: 2002-11-19
Classification: G06F

Abstract:
A data processing apparatus embodied in a single integrated circuit comprising:a central processing unit executing program instructions to manipulate data; at least one level one cache connected to said central processing unit temporarily storing at least one of program instructions for execution by said central processing unit and data for manipulation by said central processing unit, said at least one level one cache including a level one instruction cache connected to said central processing unit temporarily storing program instructions for execution by said central processing unit, and a level one data cache connected to said central processing unit temporarily storing data for manipulation by said central processing unit; a level two unified cache temporarily storing instructions and data for supply to said at least one level one cache; a directly addressable memory including at least some addresses cacheable in said at least one level one cache; a direct memory access unit connected to said directly addressable memory and adapted for connection to an external memory, said direct memory access unit transferring data between said directly addressable memory and the external memory; wherein said at least one level one cache performs a snoop cycle upon a direct memory access unit write to a cacheable address within said directly addressable memory; wherein said level one data cache performs a snoop cycle upon a direct memory access unit read of a cacheable address within said directly addressable memory by invalidating a cache entry upon a snoop hit if said cache entry is not modified within said level one data cache, and transferring a cache entry to said directly addressable memory upon a snoop hit if said cache entry is modified within said level one data cache; and said directly addressable memory merges any cache entry transferred from said level one data cache upon a snoop cycle before performing the direct memory access read.