I'm using FreeRTOS on STR910-EVAL , and it has uIP's demo webserver . I evaluate the webserver speed , and it's very slow ( about 10KB/s ~ 8KB/s ) . I put a 400KB file on webserver and download it , the speed is very slow .

I don't know why is the speed so slow .

uIP is designed for systems with little RAM. It is great for this purpose but makes some compromises to achieve it. The main limiting factor is that it will only allow one un-acked packet at any one time. This means you have to wait for the host to ack the packet before the next is sent.

If you are talking to a PC then normally the PC software (windows/Linux) will try to minimise network traffic by acking several packets at the same time. It therefore delays before sending an ack. uIP will therefore be slowed down as the delay period expires before it gets the ack, and sends the next packet.

If you have control over both ends of the TCP/IP link then you can remove the delay and get it working quickly. If not then you might be better using lwIP, which does not have the same limitation but at the expense of using more RAM.