Method and apparatus for providing virtual DMA capability on an adapter connected to a computer system bus with no DMA support

An adapter card which provides virtual direct memory access (DMA) capability while connected to a computer system bus without DMA support, the adapter card comprising:

• a non-DMA-capable bus interface;
• adapter card processing circuitry having an on-card, DMA, capable bus interface;
• a cache data memory;
• an interface circuit for providing virtual DMA capability to the adapter card processing circuitry, the interface circuit connected to the cache data memory and disposed between the non-DMA capable bus interface and the on-card, DMA-capable bus interface, the interface circuit having a multiplexer array for alternatively interconnecting the cache data memory to the DMA and non-DMA capable bus interfaces;
• and
• a flash buffer memory disposed between the interface circuit and the non-DMA capable bus interface.

An interface circuit for providing virtual direct memory access (DMA) capability to an adapter card connected to a computer system bus without DMA support, the interface circuit comprising:

• connections for a DMA-capable bus;
• connections for a non-DMA-capable bus;
• connections for a cache memory;
• a multiplexer array disposed between the DMA and non-DMA capable bus connections and the cache memory connections, the multiplexer array for alternatively interconnecting a cache memory to a DMA and a non-DMA capable computer bus;
• and
• logic for controlling a cache memory and the multiplexer array, the logic connected to the multiplexer array and the cache memory connections.

A computer implemented method for providing virtual direct memory access (DMA) data transfers between an adapter card and a host computer system having a bus with no DMA capability, the method comprising the steps of:

• opening a common memory window between host system memory and a data cache memory on the adapter card;
• requesting that data be moved between the host system memory and adapter card processing circuitry;
• determining that data is to be moved from the adapter card processing circuitry to host system memory;
• transferring a DMA packet to the data cache memory from the adapter card processing circuitry;
• notifying the host computer system that the DMA packet has been transferred;
• and
• transferring the DMA packet from the data cache memory to the host system memory.

A computer implemented method for providing virtual direct memory access (DMA) data transfers between a host computer system having a bus with no DMA capability and an adapter card, the method comprising the steps of:

• opening a common memory window between host system memory and a data cache memory on the adapter card;
• requesting that data be moved between the host system memory and adapter card processing circuitry;
• determining that data is to be moved from host system memory to the adapter card processing circuitry;
• transferring a DMA packet from host system memory to the data cache memory on the adapter card;
• and
• loading the DMA packet into the adapter card processing circuitry.

A computer program product comprising:

• a computer usable medium having a computer readable program embodied therein for causing virtual direct memory access (DMA) transfers on an adapter card attached to a computer bus without DMA support, the computer readable program in said computer program product further comprising:
• computer readable program code for causing a computer to effect the opening of a common memory window between host system memory and a data cache memory on the adapter card;
• computer readable program code for causing a computer to effect the requesting that data be moved between the host system memory and adapter card processing circuitry;
• computer readable program code for causing a computer to effect the determining of a direction of data movement;
• computer readable program code for causing a computer to effect the transferring of a DMA packet between the data cache memory and the adapter card processing circuitry;
• computer readable program code for causing a computer to notify a host computer system that data is to be moved;
• and
• computer readable program code for causing a computer to effect the transferring of a DMA packet between the data cache memory and the host system memory.