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Address issues in embedding TCP/IP (Part 3)

Posted: 12 Apr 2013     Print Version  Bookmark and Share

Keywords:code footprint  TCP/IP  network buffers 

This third instalment focuses onµC/TCP-IP data footprint. Read Part 1 here, and part 2 here.

Cutting protocols out of the code will reduce the code footprint with little impact on the data (i.e., RAM) footprint. The greatest impact on the data footprint is a result of the number of "objects" such as network buffers and connections, and most specifically from network buffers.

Data usage estimates are provided to complement the code footprint discussion. There are multiple modules requiring data to operate. Many of the data sizes calculated in the following sub-sections assume 4B pointers. The data requirements for each of the objects must be added, as needed by the configuration of the TCP/IP stack. The configuration of the objects is represented in a formula for each.

Buffer requirement
µC/TCP-IP stores transmitted and received data in data structures known as network buffers.µC/TCP-IP's buffer management is designed with embedded system constraints in mind. The most important factor on the RAM footprint is the number of buffers. For this reason, three types of buffers are defined: large receive, large transmit and small transmit buffers.

The data space for EACH network interface's buffers is calculated as:

These calculations do not account for additional space that may be required for additional alignment requirements. Also, the (minimum) recommended defaults for network buffer sizes:

About the author
Christian Legare is from Micrium.

To download the PDF version of this article, click here.





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