Trigger points for performance optimization in bus-to-bus bridges

In a bridge coupling an initiating bus to a target bus through a data buffer, a method comprising:

• receiving a write request on the initiating bus;
• checking the content of a control register to determine a non-full state of the buffer, being an adjustable minimum amount of space equal to one or more data blocks, that must be available in the buffer before the write request may be accepted;
• and
• signaling a retry on the initiating bus if the buffer does not have the minimum amount of space, and beginning a write access to transfer data from the initiating bus to the buffer if the buffer has the minimum amount of space.

In a bridge coupling an initiating bus to a target bus through a data buffer, a method comprising:

• programming a write request control condition into a control register to specify an adjustable minimum number of data blocks to be stored in the buffer before any of the blocks can be transferred from the buffer to the target bus;
• receiving a write request on the initiating bus;
• determining the write request control condition of the buffer by checking the control register;
• transferring data blocks from the initiating bus to the buffer until the queue has met the write request control condition;
• and then
• requesting the target bus to transfer said data blocks from the buffer to the target bus.

In a bridge coupling an initiator on an initiating bus to a target on a target bus through a data buffer, a method comprising:

• receiving a request for a read transaction on the initiating bus for a plurality of data blocks;
• receiving a subsequent read request for the plurality of data blocks on the initiating bus, prior to completing the read transaction on the target bus;
• determining the minimum number of data blocks that must be received in the buffer by checking a control register which allows the minimum number of data blocks to be adjusted;
• and
• servicing the subsequent read request by transferring the read data from the buffer to the initiator only if the buffer contains the minimum number of data blocks indicated by the control register.

An apparatus comprising:

• first and second bus interfaces;
• a buffer to store a plurality of blocks of data to be transferred from the second bus interface to the first bus interface as part of a read transaction initiated over the first bus interface;
• and
• a control register to indicate the minimum number of blocks that must be received in the buffer from the second bus interface before any of said data blocks may be moved from the buffer to the first bus interface in response to a subsequent read request that followed an initial read request initiated over the first bus interface.