Transparent direct memory access

摘要

A transparent direct memory access method comprises emulating an ISA-bus mapped direct memory access controller (ISA-DMAC) with a PCI-bus mapped direct memory access controller (PCI-DMAC). The ISA-DMAC exists, but there may not actually be any resources mapped into the ISA-bus space. Write snooping by the PCI-DMAC of a PCI-bus processor detects whenever an attempt is made to write the ISA-DMAC, and copies the data written into the ISA-DMAC registers into a corresponding register of the PCI-DMAC. The direct memory access operation commanded by the PCI-bus processor of the ISA-DMAC is performed by the PCI-DMAC in the PCI-bus resource space. When the direct memory access operation is completed, the PCI-DMAC updates its registers and does a write back to update the ISA-DMAC registers. The PCI-bus processor can then read the PCI-DMAC directly for status, or if legacy software is running the ISA-DMAC will respond with the appropriate register value.