[lwip-devel] Re: porting to a virtual ethernet

[yh]

Hello,

Sorry I am new to lwip, please advice me if this is not a proper list for
discussing following issues.

I am currently porting lwip to a virtual Ethernet application. Basically,
the applications and lwip are running on one device via a backplane bus to
a Fiber Ethernet on another device. The Fireber Ethernet device is a dumb
device, it does not process the packets, only extracts encapsulated
Ethernet frame from backplane bus to Fiber Ethernet or vise versa. The
structure is brieflly descripbed as follows.

apps <-> lwip <-> backplane bus <-> Fiber Ethernet
<--- Device 1 --->                 <-- Device 2 -->

The maximum size of frames on backplane bus is 512. The bp_read and
bp_write are used for Rx and Tx on backplane device driver.

I am currently using contrib/ports/unix/proj/minimal as an example for an
initial experiment, the mtu is set to 512. I guess that the lwip should
work packets segmentation with small mtu such as 512, but please correct
me if it is not.

The major issue for me is the low level interface. I have read the lwip
document, if I take the mintapif.c as an example, I guess our backplane
device driver bp_write should be assigned to both netif->output and
netif->linkout, and the bp_read should be assigned to netif->input, is it
correct?

I haven't got my real board for testing, but please advice me if my
understanding for above concept or implementation is wrong or flawed, or
if I am missing something. Please also point me a reference if there has
already been an example for above porting.

Thank you for your excellent work, the lwip is really impressive.

Jim