Ethernet on AVR

The CS8900 got a minor problem in 8-bit mode. Sometimes it stops raising interrupts. Could be easily fixed be polling the chip from time to time.

With the RTL8019AS take care, that you can't use the upper 8k internal RAM. Another problem is, that the AVR cannot "stetch" memory cycles if the chip raises IOCHRDY. This can be fixed by emulating the external memory interface by port bits, but that's much slower than using AVR's native memory interface.

For 100 Mbps we use the LAN91C111. Sometimes it doesn't free it's internal packet buffers. May be caused by the

8-bit mode, because I never found any similar problem report about the Linux driver. Could be fixed by resetting the MAC.

All three chips are supported by the Ethernut's Open Source TCP/IP stack, running on an ATmega128

Regards, Harald

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better

My choices are: SMC LAN91C96 for 10 Mbit/s and SMC LAN91C111 for 10/100 Mbit/s, though they may be a little on the expensive side for an AVR project.

Tauno Voipio tauno voipio @ iki fi

In addition to those mentioned by Harald, there is the W3100 from Wiznet

I use it with a ATmega161.

It is 100Mbit and has a hardware TCP/IP stack. It is limited to four connections. However, I have had some problems with strange things going on, if a TCP-socket is closed while there is still unacknowleged data. I haven't spend the time to track this down.

Also the documentation leaves out a few things, which you should know, when you try to optimize chip access.

Nevertheless, I'm quite satisfied with this little beast.

A real bonus is indirect addressing (with optional auto-inc). So, you only need 4-byte address-space.

A real bad thing for some applications might be, that you don't have much influence on the packet handling (e.g. AFAIK you can't flush the buffer).

BTW: Tech-Support-Forum on their Website was quite fast and good.

/Jan-Hinnerk

Check out

for some good prototyping resources. They offer proto boards for PIC and AVR with RTL8019AS, CS8900, and ASIX

10/100, along with driver code to get you going.

They used to offer a suite of NIC proto boards with headers pinned to match the AVR proto board. I imagine if you asked, they'd still sell them.

Richard

better

Thanks for all the suggestions so far. Especially to Richard for pointing me to

. I ordered their AVR board.

Meindert