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| Method and apparatus for reordering packet data units in storage queues for reading and writing memory |
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Network device and method of controlling flow of data arranged in frames in a data-based network
| Details |
Inventors: Kasper, Christian D.;
Assignee: STMicroelectronics, Inc. (Carrollton, TX)
Primary Examiner: Lee; Thomas
Assistant Examiner: Perveen; Rehana
Attorney, Agent or Firm: Jorgenson; Lisa K., Regan; Christopher F.
A method and network device are disclosed using a look-ahead watermark in a FIFO memory. In accordance with the present invention, a watermark interrupt is generated from a FIFO memory when data in the FIFO memory has crossed a watermark threshold. A data burst is transferred through a direct memory access unit to the FIFO memory. A look-ahead watermark flag is checked at the FIFO memory to determine if sufficient memory space exists inside the FIFO memory for an additional data burst, which is transferred through the direct memory access unit to the FIFO memory when the look-ahead watermark flag indicates that sufficient memory space is available. |
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DETAILED DESCRIPTION It is therefore an object of the present invention to enable FIFO filling without incurring the same overhead expenses as required for a previous watermark interrupt command.
It is still another object of the present invention to provide a method and apparatus, including a network device, for transmitting data into a FIFO memory, which allows additional bursts of data without overflow.
The present invention is now advantageous because the invention provides a look-ahead watermark that functions as a synchronizing signal in a FIFO memory structure to indicate that sufficient storage exists to receive one or more additional write bursts.
Transmission of frames can be expedited because it effectively increases bus and memory resource utilization while reducing the processor context switching.
The look-ahead watermark implies that the FIFO can accommodate an additional DMA burst of the indicated quantity.
The DMA burst size is not required to be the same size as the look-ahead watermark mediated burst.
The look-ahead watermark functions more as a "capacity-indicator" than as a conventional transmit watermark mechanism.
In another respect, the look-ahead watermark is "top-down" capacity indicator versus a standard "bottom-up" watermark.
The look-ahead watermark provides a "window" into the FIFO memory.
Once an initial command to a DMA has been issued, the firmware that is part of a CPU (e.
g.
, communications processor) can check a DMA flag, which indicates that the burst has successfully completed.
The firmware then can examine the look-ahead watermark flag to determine if sufficient space exists inside the FIFO for an additional write burst.
The look-ahead watermark also has the additional benefit that allows a second command to be constructed and submitted without incurring the same overhead expenses as required for the first command.
It is always the same "type" of command, so no additional firmware resolution logic is required.
In accordance with the present invention, a method of controlling flow of network based data arranged in frames, and a network device is disclosed and claimed
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