[lwip-users] Are there any safe ways to bypass the tcp_write() and/or tcp_output() call stack?

[Howard Li]

The microcontroller I am working with is a TMS320F28388D.

https://www.ti.com/product/TMS320F28388D

The application I am writing for the microcontroller uses TCP communication and has tight timing constraint requirements for outgoing data; thus a need for very high TCP throughput.

Examination of the source code revealed the following call stack starting at tcp_output().

tcp_output()

V V V

tcp_output_segment()

V V V

ip4_output_if()

V V V

ip4_output_if_src()

V V V

etharp_output()

V V V

etharp_output_to_arp_index()

V V V

ethernet_output()

V V V

(platform-specific packet sending function)

That is an 8 levels deep function call stack (when including tcp_output())! Even with hardware checksum generation turned on and software checksum generation turned off, I am still not getting the performance that I need. I am seriously considering the possibility of pre-defining a TCP/IP packet, changing parts of it whenever I need to send new data, and using the platform specific packet sending function to do the sending. However, I am not sure how well this will play with the TCP PCBs used for establishing the connection in the first place (more specifically I am concerned about handling the acknowledgement of packets sent via the shortcut strategy instead of tcp_write()).

Sincerely,

Howard Li