Sharing Data Between CPU and Peripheral Devices

Sharing Data Between CPU and Peripheral Devices

To avoid memory contamination, the CPU and any other device capable of DMA must not both be allowed to write data to separate parts of a double-word in memory. Since CPU accesses to smaller portions of a double-word are performed as read-modify-write operations, they are not atomic, and could be interleaved with data written by a device between the CPU read operation and the CPU write operation. Make sure that data written by a device does not fall within the same double-word as data written by the CPU.