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Example with LWIP +Zero-copy ethernet driver

Posted by Anis Ben Abdallah on January 15, 2010
Hi,

Please I would like to know if you have any example with FreeRTOS and LWIP, using a zero-copy ethernet driver (no copy from receive ethernet driver buffer to stack buffer) .

I tried to look at many LWIP examples in FreeRTOS package, but I don't see any implementing such mechanism.

Thanks,
Anis

RE: Example with LWIP +Zero-copy ethernet driver

Posted by Dmitri Snejko on January 15, 2010
I think it is a question not to FreeRtos forum but more to LwIP forum. I don't like to say it is impossible to implement a zero-copy driver for LwIP but it should really depend on your hardware. The main idea was discussed already in LwIP forum: you should set pbuf size to maximum packet size, preallocate some pbufs for MAC buffers and replace any taken buffer with a new preallocated pbuf. For sending it is easier just deallocate the sent pbuf and return it back to LwIP. Some problems may arise: most MACs with DMA will need right alignment for the buffers so it could be tricky since pbufs have byte alignment.

Regards.

RE: Example with LWIP +Zero-copy ethernet driver

Posted by Anis Ben Abdallah on January 15, 2010
Thanks for these interesting infos.

I'm using an STM32 micro with ethernet, according to the doc, the MAC DMA supports byte aligned buffers, so this may help to easly implement a zero-copy driver.

Regards,
Anis


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