[lwip-users] lwiperf together with TinyUSB / NCM and small MSS

[Hardy Griech]

Hello,

I made a rewrite of the TinyUSB NCM device which allows lwIP via USB, see https://github.com/hathach/tinyusb/pull/2227.

During testing I observed that "iperf -c 192.168.14.1 -e -i 1 -M 100 -l 8192 -r" does not work in the direction device ->host.  The same is true if one chooses ECM as TinyUSB device.  Also "iperf -c 192.168.14.1 -e -i 1 -M 1000 -l 8192 -r" works.

After fiddling around, I have found, that reducing txlen_max in lwiperf_tcp_client_send_more() to 700 makes the problem disappear so that iperf is working for all MSS sizes.

With the original code tcp_output() did not generate lwiperf_tcp_client_sent() callbacks for small MSS sizes.

Can anybody confirm this iperf behavior preferably without TinyUSB?

Hardy