PCI Express System Architecture

Flow Control Updates Following FC_INIT

The receiver must continually update its neighboring device to report additional Flow Control credits that have accumulated as a result of moving transactions from the Flow Control buffer. Figure 7-13 on page 309 illustrates an example where the transmitter was previously blocked from sending header transactions because the Flow Control buffer was full. In the example, the receiver has just removed three headers from the Flow Control buffer. More space is now available, but the neighboring device has no knowledge of this. As each header is removed from the Flow Control buffer, the CREDITS_ALLOCATED count increments. The new count is delivered to the CREDIT_LIMIT register of the neighboring device via an ...