Weekly driver 4: ENC28J60, Ethernet for your microcontroller

March 13, 2018 by Jorge Aparicio

It’s week number 11 and the weekly driver #4 is out! Last time, I did drivers 1 and 2 so you may be wondering where’s driver 3? Driver #3, the MCP3008, was covered by @pcein in their blog. Also, as of now there are at least 14 (!) drivers being worked on by the community.

This week I’m releasing a driver for the ENC28J60, an Ethernet controller with SPI interface. This IC lets you connect your microcontroller, if it has a SPI interface, to a Local Area Network or, with more work, to the internet. Apart from the IC you need a RJ45 connector and a few other components so I’m using this module which has the ENC28J60 and all the required components on a single board.

ENC28J60

enc28j60

The driver crate, the enc28j60, that lets you interface this chip is kind of boring – as all drivers should be: boring and with no surprises in them.

To initialize a driver you pass something that implements the SPI traits from the embedded-hal crate plus a nCS (Clock Select) pin. You can optionally pass the INT and RESET pins; if you pass the INT (interrupt) pin you can make use of the interrupt API; if you pass the RESET pin then initialization will use that to reset the ENC28J60 instead of using a software reset. You also need to pass something that provides delay functionality; a delay is needed in the initialization because silicon bugs are a thing 1. Finally, you have to pass the size of the internal RX (reception) buffer and the MAC address that the device will use.

let mut enc28j60 = Enc28j60::new(spi, ncs, int, reset, &mut delay, 7 * KB, MAC)?;

The SPI interface usually runs at a lower rate (e.g. 1 Mbps) than the Ethernet interface (10 Mbps) so it’s not possible to move the incoming data into the microcontroller memory as it arrives. That’s why the ENC28J60 has 8 KB of RAM; in that memory it stores (buffers) all the incoming data until the microcontroller has a chance to read it out. This memory is also used to store the data to transmit so it’s necessary to split the 8 KB in two regions: one for transmission (TX) and one for reception (RX). That’s what the 7 KB in the code snippet is all about: it’s the size of the RX part.

To send out data you use the transmit method. This method copies (in a blocking fashion) the specified bytes into the ENC28J60 memory and starts a transmission.

enc28j60.transmit(bytes)?;

transmit won’t block until the transmission is finished though. For that you can use the flush method.

enc28j60.flush()?;

But note that the current implementation of transmit will flush any in progress transmission. This may be lifted in the future to let you queue several frames to send in the ENC28J60 memory.

The bytes you transmit should be a valid Ethernet frame otherwise the recipient is likely to discard your data. In the current API bytes has type &[u8], which means that it’s up to the caller to ensure that the data is a valid Ethernet frame. The driver doesn’t demand any more elaborated (new)type to let you use it with any network stack you want.

As per the spec Ethernet frames must include a frame check sequence (a CRC) at their end. The ENC28J60 takes care of computing that and appending it to the frame so the microcontroller doesn’t have to deal with it. The ENC28J60 will also take care of padding bytes so the frame meets the minimum length of 64 bytes.

To check if there’s new data available you have the pending_packets method which returns the number of packets that are stored in the ENC28J60 memory and that still need to be processed (read out).

let pending_packets = enc28j60.pending_packets()?;

Once you have confirmed that there are packets that still need to be processed you can read them out using the receive method.

let buf = [0; 256];
while enc28j60.pending_packets()? > 0 {
    let n = enc28j60.receive(&mut buf)?;
    let frame = &buffer[..n as usize];
    // ..
}

receive pretty much mimics the API of std::io::Read::read but returns the number of bytes read as a u16 value because that’s the smallest integer type that makes sense in this case (remember: only 8 KB of memory).

Note that the ENC28J60 contains a receiver filter and that, by default, will filter out (ignore) packets with invalid CRC, unicast packets that are not addressed to the MAC of the ENC28J60 and packets that are not broadcasts.

That’s the description of the boring driver now let’s look at some demos!

Demos

(All these demos were tested on the Blue Pill development board.)

ping

The first demo is a “pong server” (code here). Basically, it’s a program that responds to the ping command.

If you ping the hardcoded IP address of the microcontroller you’ll see this:

$ # remove the IP and MAC address of the microcontroller from the ARP cache
$ _ arp -d 192.168.1.33

$ ping -c3 192.168.1.33
PING 192.168.1.33 (192.168.1.33) 56(84) bytes of data.
64 bytes from 192.168.1.33: icmp_seq=1 ttl=64 time=28.4 ms
64 bytes from 192.168.1.33: icmp_seq=2 ttl=64 time=15.6 ms
64 bytes from 192.168.1.33: icmp_seq=3 ttl=64 time=15.6 ms

--- 192.168.1.33 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 15.674/19.950/28.497/6.043 ms

For comparison here’s the output of pinging my router:

$ ping -c3 192.168.1.1
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=2.24 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=2.22 ms
64 bytes from 192.168.1.1: icmp_seq=3 ttl=64 time=2.18 ms

--- 192.168.1.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 2.188/2.219/2.240/0.022 ms

The Round Trip Time (RTT) is 86% smaller in the case of the router.

The microcontroller will also log a bunch of stuff to the ITM. Here are the logs that were generated during the execution of the first ping command:

$ itmdump -f /dev/ttyUSB0
Rx(60)
* ether::Frame { destination: mac::Addr([0xff, 0xff, 0xff, 0xff, 0xff, 0xff]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Arp }
** arp::Packet { oper: Request, sha: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), spa: ipv4::Addr([192, 168, 1, 11]), tha: mac::Addr([0x00, 0x00, 0x00, 0x00, 0x00, 0x00]), tpa: ipv4::Addr([192, 168, 1, 33]) }

** arp::Packet { oper: Reply, sha: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), spa: ipv4::Addr([192, 168, 1, 33]), tha: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), tpa: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Arp }
Tx(42)

Rx(98)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 4374, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa616, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** icmp::Packet { type: EchoRequest, code: 0, checksum: 0x5638, id: 22953, seq_no: 1 }

*** icmp::Packet { type: EchoReply, code: 0, checksum: 0x5e38, id: 22953, seq_no: 1 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 4374, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa616, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(98)

Rx(98)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 5023, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa38d, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** icmp::Packet { type: EchoRequest, code: 0, checksum: 0x1531, id: 22953, seq_no: 2 }

*** icmp::Packet { type: EchoReply, code: 0, checksum: 0x1d31, id: 22953, seq_no: 2 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 5023, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa38d, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(98)

Rx(98)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 5092, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa348, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** icmp::Packet { type: EchoRequest, code: 0, checksum: 0x2c29, id: 22953, seq_no: 3 }

*** icmp::Packet { type: EchoReply, code: 0, checksum: 0x3429, id: 22953, seq_no: 3 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 5092, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa348, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(98)

There are four exchanges in these logs: 1 ARP exchange and 3 ICMP exchanges. Let’s look at them in more detail.

ARP

The first exchange is this ARP exchange.

Rx(60)
* ether::Frame { destination: mac::Addr([0xff, 0xff, 0xff, 0xff, 0xff, 0xff]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Arp }
** arp::Packet { oper: Request, sha: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), spa: ipv4::Addr([192, 168, 1, 11]), tha: mac::Addr([0x00, 0x00, 0x00, 0x00, 0x00, 0x00]), tpa: ipv4::Addr([192, 168, 1, 33]) }

** arp::Packet { oper: Reply, sha: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), spa: ipv4::Addr([192, 168, 1, 33]), tha: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), tpa: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Arp }
Tx(42)

In these logs Rx($N) indicates that $N bytes were received – the 4 bytes of the CRC are not included in this number. The lines below the Rx($N) line correspond to the headers found in the received data. As we are dealing with Ethernet frames the first header will always be an Ethernet frame. In this case, the payload of the Ethernet frame is an ARP packet.

The Tx($N) in the logs indicate that the $N bytes were sent to the ENC28J60 for transmission – this number doesn’t include the CRC or the zero padding that the ENC28J60 appends to the frame. The lines above the Tx($N) line indicate the headers included in the transmitted data.

So, what’s this ARP thing?

My laptop wants to ping the microcontroller and knows its IP address: 192.168.1.33 (that’s the first argument of the ping command) but it doesn’t know its MAC address, which is required to send an Ethernet frame.

Before actually pinging the microcontroller the laptop will first broadcast (MAC address = ff:ff:ff:ff:ff:ff) an ARP request. The request basically asks everyone on the LAN: “what’s the MAC address (THA: Target Hardware Address) of the machine with IP address (TPA: Target Protocol Address) 192.168.1.33?”

When the microcontroller sees its IP in this request it will answer with another ARP packet indicating that its MAC address (SHA: Sender Hardware Address) is 20:18:03:01:00:00 and that its IP address (SPA: Sender Protocol Address) is 192.168.1.33.

From this exchange the microcontroller also learns the MAC address and IP address of my laptop: this information is in the SHA and SPA fields of the received ARP packet.

So, the Address Resolution Protocol (ARP) is used to find out how Protocol Addresses, like IPv4 addresses, map to Hardware Addresses, like MAC addresses – at least within a LAN and when using IPv4 as the data link layer.

ICMP

What the ping command does under the hood is send ICMP packets of the EchoRequest type to the specified IP address. Machines that receive this kind of ICMP packet must respond with ICMP packets of the EchoReply type. The ping program processes these responses and shows some statistics about the exchange like the Round Trip Time and the hop distance between the nodes (cf. ttl).

Back to the exchange, once my laptop learned the MAC address of the microcontroller it started sending ICMP packets. The first ICMP exchange is shown below:

Rx(98)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 4374, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa616, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** icmp::Packet { type: EchoRequest, code: 0, checksum: 0x5638, id: 22953, seq_no: 1 }

*** icmp::Packet { type: EchoReply, code: 0, checksum: 0x5e38, id: 22953, seq_no: 1 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 84, identification: 4374, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Icmp, checksum: 0xa616, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(98)

The first thing to note is that this time the destination MAC address specified in the received Ethernet frame is the MAC address of the microcontroller, and not the broadcast address. The payload of the Ethernet frame this time is an IPv4 packet and the payload of that packet is an ICMP packet.

As expected the ICMP packet is of the EchoRequest type. Its id (identifier) field indicates the PID of the ping command, and the seq_no (sequence number) field tracks the number of packets send by the ping command. If you look at the full log you’ll see that id remains constant across all the ICMP exchanges whereas seq_no monotonically increases.

The microcontroller sends back a EchoReply packet in response to this EchoRequest packet. Most of the information in the headers, like the id and seq_no fields, as well as the payload of the request are preserved in the reply.

Benchmark

The pong server I showed works fine but it’s wasteful because it busy waits for new packets so I partially rewrote it to be reactive: now it sleeps most of the time and only wakes up to process newly received packets. It does this using the INT (interrupt) pin as a source of interrupts: the ENC28J60 notifies the microcontroller about new packets by driving the INT pin low and this wakes up the microcontroller.

To this version I also added a CPU monitor with the goal of being able to benchmark the performance of the pong server. Then I benchmarked the final version by spawning several parallel instances of the ping command. The results are shown below:

pings CPU usage during one second (worst of 10 samples)
1 0.6591%
2 0.8111%
4 1.8581%
8 3.2091%
16 6.3993%
32 12.8010%

I should note that the CPU was operating at 8 MHz, that logs were disabled during the collection of these statistics and that the driver only exposes a blocking API 2 at the moment so CPU usage could actually be reduced in the future.

UDP

The second demo is a UDP echo server (the code is the same as the first demo’s). This program will send back all the received UDP datagrams, regardless of what their destination port is.

You can test this demo using netcat:

$ nc -u 192.168.1.33 1337
hello
hello
Rustaceans
Rustaceans

The server will echo back everything you send to it.

Here are the logs captured during that UDP exchange:

$ itmdump -f /dev/ttyUSB0
Rx(60)
* ether::Frame {destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 34, identification: 3907, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0xa80b, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** udp::Packet { source: 58248, destination: 1337, length: 14, checksum: 20407 }

*** udp::Packet { source: 1337, destination: 58248, length: 14, checksum: 0 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 34, identification: 3907, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0xa80b, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x0, 0x00]), type: Ipv4 }
Tx(48)

Rx(60)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 39, identification: 4839, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0xa462, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** udp::Packet { source: 58248, destination: 1337, length: 19, checksum: 36455 }

*** udp::Packet { source: 1337, destination: 58248, length: 19, checksum: 0 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 39, identification: 4839, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0xa462, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(53)

This time we have UDP datagrams, instead of ICMP packets, inside the IPv4 packets. I should note that the echo server doesn’t bother with updating the checksum of the UDP datagrams and just zeroes it 3; that’s why you see that all the responses have their UDP checksum set to zero.

I think this is a good time to show the binary size of the demo program:

$ arm-none-eabi-size enc28j60
   text    data     bss     dec     hex filename
   7158       0       4    7162    1bfa enc28j60

This size is with the logging functionality removed.

CoAP

The third and final demo (code here) is a simple CoAP server.

If you are not familiar with the Constrained Application Protocol (CoAP) it’s, more or less, a simplified version of HTTP that runs on top of UDP (HTTP uses TCP as its transport layer). In CoAP you also have GET, PUT, POST and DELETE methods that you can use to implement RESTful APIs.

The difference between HTTP and CoAP is that CoAP has been designed to run on resource constrained nodes; its RFC explicitly mentions “8-bit microcontrollers with small amount of ROM and RAM” as an example of the environments it targets.

In this demo the CoAP server exposes a single resource: an LED at path /led. The state of the LED can be queried / modified using GET / PUT requests, respectively.

The jnet crate provides a simple CoAP client that you can use to interact with the CoAP server.

This is how a GET request looks like:

$ coap GET coap://192.168.1.33/led
-> coap::Message { version: 1, type: Confirmable, code: Method::Get, message_id: 0, options: {UriPath: "led"} }
<- coap::Message { version: 1, type: Acknowledgement, code: Response::Content, message_id: 0, payload: "on" }
on

And this is how a PUT request looks like:

$ coap PUT coap://192.168.1.33/led off
-> coap::Message { version: 1, type: Confirmable, code: Method::Put, message_id: 0, options: {UriPath: "led"}, payload: "off" }
<- coap::Message { version: 1, type: Acknowledgement, code: Response::Changed, message_id: 0 }

Here’s a video where I interact with the CoAP server to control the LED:

And here are the logs collected during the first two CoAP requests:

$ itmdump -f /dev/ttyUSB0
Rx(60)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 37, identification: 20643, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0x66a8, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** udp::Packet { source: 11983, destination: 5683, length: 17, checksum: 57209 }
**** coap::Message { version: 1, type: Confirmable, code: Method::Get, message_id: 0, options: {UriPath: "led"} }

**** coap::Message { version: 1, type: Acknowledgement, code: Response::Content, message_id: 0, payload: "off" }
*** udp::Packet { source: 5683, destination: 11983, length: 16, checksum: 0 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 36, identification: 20643, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0x66a9, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(50)

Rx(60)
* ether::Frame { destination: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), source: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), type: Ipv4 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 39, identification: 22193, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0x6098, source: ipv4::Addr([192, 168, 1, 11]), destination: ipv4::Addr([192, 168, 1, 33]) }
*** udp::Packet { source: 53402, destination: 5683, length: 19, checksum: 53048 }
**** coap::Message { version: 1, type: Confirmable, code: Method::Put, message_id: 0, options: {UriPath: "led"}, payload: "on" }

**** coap::Message { version: 1, type: Acknowledgement, code: Response::Changed, message_id: 0 }
*** udp::Packet { source: 5683, destination: 53402, length: 13, checksum: 0 }
** ipv4::Packet { version: 4, ihl: 5, dscp: 0, ecn: 0, total_length: 33, identification: 22193, df: true, mf: false, fragment_offset: 0, ttl: 64, protocol: Udp, checksum: 0x609e, source: ipv4::Addr([192, 168, 1, 33]), destination: ipv4::Addr([192, 168, 1, 11]) }
* ether::Frame { destination: mac::Addr([0x9c, 0xb6, 0xd0, 0xed, 0xad, 0xff]), source: mac::Addr([0x20, 0x18, 0x03, 0x01, 0x00, 0x00]), type: Ipv4 }
Tx(47)

This is binary size of the CoAP demo with logging functionality disabled:

$ arm-none-eabi-size enc28j60-coap
   text    data     bss     dec     hex filename
   9186       0       4    9190    23e6 enc28j60-coap

I swear that at some point the binary size of the CoAP demo was about the size of the UDP echo server. I, somehow, seem to have made some change that regressed the binary size by around 2 KB sigh. This is why I should commit more often.

Conclusion

There you go: Ethernet functionality for all devices that have a SPI interface via the ENC28J60. The driver have been kept as simple as possible to let you use it with any network stack. I’ve been doing my own network experiments in the jnet crate but you should definitively check out the smoltcp crate (I haven’t tested it myself) which is a mature network stack with actual socket abstractions – it would be great to have an example of enc28j60 + smoltcp in the stm32f103xx-hal crate!


Thank you patrons! ❤️

I want to wholeheartedly thank:

Iban Eguia, Aaron Turon, Geoff Cant, Harrison Chin, Brandon Edens, whitequark, James Munns, Fredrik Lundström, Kjetil Kjeka, Kor Nielsen, Alexander Payne, Dietrich Ayala, Kenneth Keiter, Hadrien Grasland, vitiral and 54 more people for supporting my work on Patreon.


Let’s discuss on reddit.

Enjoyed this post? Like my work on embedded stuff? Consider supporting my work on Patreon!

Follow me on twitter for even more embedded stuff.

The embedded Rust community gathers on the #rust-embedded IRC channel (irc.mozilla.org). Join us!


  1. Vendors document silicon bugs in a document called Silicon Errata. Here is the Silicon Errata for the ENC28J60; I had to work around 5 (!) silicon bugs in the driver to make it work.

    [return]
  2. Methods like transmit and receive could be made asynchronous / non-blocking with the help of the DMA but we don’t have traits for DMA based I/O in embedded-hal at the moment.

    [return]
  3. This is allowed by the spec when using IPv4 as the data link layer. [return]

Contents

Creative Commons License
Jorge Aparicio