Read ahead buffer for read accesses to system memory by input/output devices with buffer valid indication

An integrated circuit coupled between system memory of a computer system and an input/output channel, comprising:

• an input/output request circuit coupled to receive a read request for data in system memory from an input/output device over the input/output channel;
• a read ahead buffer coupled to the input/output request circuit, strong data from a previous read access to system memory, the input/output request circuit coupled to selectively provide data from one of the system memory and the read ahead buffer in response to the read request;
• and
• a control register associated with at least one input/output device, the control register specifying whether block read ahead is active for the one input/output device.

A method of operating a computer system including a read ahead buffer coupled to a memory controller and an input/output controller coupled to an input/output channel, comprising:

• receiving a read request for data from an input/output device over file input/output channel, the read request specifying an address in system memory;
• determining whether at least a portion of the data requested in the read request is in the read ahead buffer, and
• selectively providing at least the portion of the data from one of the read ahead buffer and the system memory to the input/output device in response to the read request according to whether at least a portion of the selected data is in the read ahead buffer;
• determining that data in the read ahead buffer is invalid according to at least one of an end of an input/output channel access, an end of a predetermined period of time after the read ahead buffer is indicated to be valid, access by the input/output device to an address outside of currently stored data in the read ahead buffer, and an access to an address contained in the read ahead buffer by a different input/output device;
• and
• wherein determining whether at least a portion of the data requested is in the read ahead buffer includes determining if the read ahead buffer has valid data.