High speed bus with flow control and extended burst enhancements between sender and receiver wherein counter is maintained at sender for free buffer space available
In a networked system in which high speed busses interconnect sources and destinations of data, systems for and methods of flow control and extended burst transfers are described.
1. A system for performing flow control between a sender and receiver of data interconnected by a bus in a networked system comprising:
a counter maintained at the sender;
first logic for decrementing the counter by the size of a block of data upon or after transmission of the block to the receiver;
second logic for incrementing the counter by the amount of incremental free space which has become available in one or more buffers maintained at the receiver upon or after receipt of a first command from the receiver;
third logic for comparing the contents of the counter with the size of the block while the sender is in a first state, and (1) avoiding or deferring transmitting the block to the receiver if the size of the block exceeds the contents of the counter, or (2) transmitting the data to the receiver if the size of the block does not exceed the contents of the counter; and
fourth logic for storing in the counter a value representative of the amount of absolute free space which is available in the one or more buffers upon or after receipt of a second command from the receiver.
2. The system of claim 1 further comprising fifth logic for transitioning the sender to a second state upon or after receipt of a third command from the receiver, the second state characterized by the sender transmitting data to the receiver without regard to the contents of the counter.
3. The system of claim 2 further comprising sixth logic for transitioning the sender from the second state to the first state upon or after receipt of the second command from the receiver.
4. The system of claim 1 wherein the sender and receiver are ASICs.
5. The system of claim 1 wherein the one or more buffers are FIFO buffers.
6. The system of claim 1 embodied in a sender of data in the networked system.
7. A method of performing flow control between a sender and receiver of data in a networked system, the sender configured to maintain a counter whose contents are representative of available free space in one or more buffers maintained by the receiver, the method comprising the steps of:
transmitting a block of data to the receiver while the sender is in a first state if the size of the block does not exceed the contents of the counter;
decrementing the counter with the size of a block upon or after transmitting the block;
incrementing the counter by a value representative of the amount of incremental free space which has become available in one or more buffers maintained at the receiver upon or after receipt at the sender of a first command from the receiver; and
storing in the counter a value representative of the amount of absolute free space which is available in one or more buffers maintained at the receiver upon or after receipt at the sender of a second command from the receiver.
8. The method of claim 7 further comprising:
transitioning the sender from the first state to a second state upon or after receipt of a third command from the receiver, the second state characterized by the sender transmitting data to the receiver without regard to the contents of the counter.
9. The method of claim 8 further comprising:
transitioning the sender from the second state to the first state upon or after receipt of the second command from the receiver.