Cache and DMA with a global valid bit

摘要

A digital system and method of operation is provided in which the digital system has at least one processor, with an associated multi-segment cache memory circuit (506(n). A single global validity circuit (VIG) is connected to the memory circuit and is operable to indicate if any segment of the multiple segments holds valid data. Block transfer circuitry (700, 702) is connected to the memory circuit and is operable to transfer a block of data (1650) to a selected portion of segments (1606) of the cache memory circuit. The block circuitry is operable to transfer data from a pre-selected region of the secondary memory (1650) to a particular segment of the plurality of segments and to assert the global valid bit at the completion of a block transfer. Direct memory access (DMA) circuitry (1610) is connected to the memory cache for transferring data between the memory cache and a selectable region (1650) of a secondary memory and is also operable to assert the global valid bit at the completion of a DMA block transfer. The cache can be operated in a first manner such that when a transfer request from the processor requests a first location in the cache memory that does not hold valid data, valid data is transferred (1652) from a pre-selected location in a secondary memory that corresponds directly to the first location. The cache can then be operated in a second manner such that data is transferred (1662) between the first location and a selectable location in the secondary memory, wherein the selected location need not directly correspond to the first location.