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Re: [lwip-users] Ethernet package through SPI interface

From: Sergio R. Caprile
Subject: Re: [lwip-users] Ethernet package through SPI interface
Date: Wed, 9 Mar 2016 15:03:46 -0300
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

So maybe something was lost in the translation and the vocabulary use.
To make things clear, you say you want to use an SPI interface to send
data between two hosts, and that data will be IP datagrams coming from
and going to lwIP ? So no Ethernet here, not even frames, because lwIP
does not do Ethernet stuff. Is that what you want ?
Host A SPI ---- Host B SPI
Starting again from prev mail,
Once you have a netif driver, you can do whatever you want with your
data: write it to an Ethernet controller, print a paper and attach it to
a pidgeon, it is your call. However, if your communication media is not
broadcast, you need to add a layer of intelligence to make it work.
If your comm media is serial point-to-point, which it seems (I assume
you want to treat SPI as a serial link between only two hosts), you will
need something like SLIP or PPP (or invent something similar, which I do
not recommend). Being that PPP is available and maintained...
On the SPI side of the problem, being that SPI is a master-slave
protocol, one of the ends (slave) will only be able to send IP datagrams
when the other (master) asks it to do that. That adds a new buffering
and scheduling scheme neither SLIP nor PPP solve. Maybe you can happily
thrust PPP will handling the mostly half-duplex nature of this
connection yourself.
I would go for a serial port...

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