Nicolas Nackel / Mbed 2 deprecated PPP-Blinky

Small Internet Protocol Stack using a standard serial port.

Dependencies:   mbed

PPP-Blinky - TCP/IP Networking Over a Serial Port

Note: The source code is at the bottom of this page.

/media/uploads/nixnax/blinky-connected.gif
A Windows desktop showing PPP-Blinky in the network connections list.

Describe PPP-Blinky in Three Sentences

PPP-Blinky is a tiny library that enables Internet protocols (IPv4) to any mbed target hardware by using only a serial port.

The code runs on processors with as little as 8k RAM, for example the Nucleo-L053R8 board.

PPP-Blinky uses the industry-standard PPP (Point-to-Point) Protocol and a tiny "stateless" TCP/IP stack.

No Ethernet Port Required

No ethernet port is required - PPP-Blinky uses a serial port to send IP packets to your PC.

PPP-Blinky emulates a standard dial-up modem and therefore connects to Windows, Linux or Adroid machines.

The code runs on most ARM mbed platforms such as the LPC11U24 shown in the picture below:

/media/uploads/nixnax/blinky-to-laptop1.jpg mbed LPC11u24 acting as a webserver to a Windows laptop.

Webserver

The Webserver and WebSocket functions are ideal for building browser-based GUIs on mbed-enabled hardware.

PPP-Blinky's HTTP webserver works with most web clients such as Internet Explorer, Mozilla Firefox, Google Chrome, Safari, Curl, wget and Lynx as well as Microsoft Powershell Invoke-Webrequest command.

In the image below Firefox web browser displays the main web page embedded into PPP-Blinky's code:

/media/uploads/nixnax/ppp-blinky-firefox.jpg Firefox web browser displays a web page embedded into PPP-Blinky's code

WebSocket Service

WebSocket is the most popular protocol standard for real-time bidirectional TCP/IP communication between clients and servers.
In the image below a small Internet Explorer script has connected to PPP-Blinky's WebSocket Service.
A websocket message was then sent by the browser and was echoed back by the WebSocket, triggering the onmessage event in the script.
The WebSocket service enables bidirectional real-time interaction between PPP-Blinky and any element in the browser DOM via JavaScript.
If you already have PPP-Blinky up and running you can test your WebSocket service using this: http://jsfiddle.net/d26cyuh2/112/embedded/result
Websockets are ideal for building browser-based GUIs for mbed hardware.

/media/uploads/nixnax/ppp-blinky-websocke-2.gif

Trying PPP-Blinky on your mbed board

You will need an mbed-enabled hardware board: https://developer.mbed.org/platforms/

Establish a serial port connection between your host PC and your mbed board. The easiest way is to use mbed hardware with a USB serial debug port. I've tried the ST-Micro Nucleo-L476RG, Nucleo-L152RE, Nucleo-F401RE, Nucleo-L432KC, Nucleo-L053R8, mbed-LPC11U24 and mbed-LPC1768 boards and they all work out of the box. Use the mbed online compiler to compile the software for your target board. Save the compiled binary to your hardware.

Before establishing a network connection, you can verify the operation of the code by opening a terminal program such as Tera Term, and setting the baud rate of the COM port on your mbed board to 115200 baud. LED1 should toggle for every two 0x7E (~) (i.e. tilde) characters you type, as 0x7E is the PPP frame start/end marker. Don't forget to close the port when your'e done testing, or else Windows Dial-up Networking will report that the COM port is in use by another program when you try to connect.

Once you are certain that the serial port and firmware is working, proceed to creating a new network connection on your PC -see below.

Creating a Dial-up Connection in Windows

/media/uploads/nixnax/modem.jpg

Setting up Dial-Up Networking (DUN) on your Windows 7 or 8 PC is essentially a two-step process: First, you create a new modem device, because PPP-blinky partially emulates a standard Windows serial port modem device. Second, you create a new Internet connection (in practice, a new network adapter) which is associated with your new "modem".

Step-by-step description of how to configure Windows for PPP-Blinky here:

/users/nixnax/code/PPP-Blinky/wiki/Configuring-Windows-Dial-Up-Networking

There is also a screen on how to set up Linux dial-up networking near the bottom of this page.

Connecting to PPP-Blinky from your PC

Once Windows networking is configured you can establish a dial-up connection to your mbed board over the USB virtual com port.

The IP address you manually assigned to the new dial-up network adapter (172.10.10.1) functions as a gateway to any valid IP address on that subnet. In the screen capture below, I'm sending pings from the Windows 8 command line to my ST-Micro Nucleo-L476RG board over the USB virtual serial Port. I'm also using a second serial port and Tera Term to capture the debug output from a second serial port on the hardware. The optional debug output from the board prints out the IP source and destination address and the first few bytes of the data payload. Note that the source is the adapter IP address, (172.10.10.1 in this case) and the destination is some other address on that subnet - all packets to the subnet are sent to our mbed hardware. For example, you could also ping 172.10.10.123 or, if your PPP-Blinky is running, simply click on this link: http://172.10.10.123

/media/uploads/nixnax/ping-cap-3.gif

One Million Pings!

In the image below the ICMP ("ping") echo reply service was tested by sending one million pings to ppp-Blinky. This took over two hours.
The ping tool used on the Windows 8 PC was psping.exe from PsTools by Mark Russinovich - http://bit.ly/PingFast
The average reply time for a short ping (1 byte of payload data) was 11 milliseconds at 115200 baud on the $10 Nucleo-L053R8 board - barely enough time for 130 bytes to be sent over the port!

/media/uploads/nixnax/ppp-blinky-ping-results.jpg

Monitoring PPP-Blinky Packets

The image below is from a Microsoft Network Monitor 3.4 capture session.

Responses from PPP-Blinky are shown in blue.

Frame 2 - Internet Explorer at IP 172.10.10.1 (the Dial-Up Adapter IP) requests a TCP connection by sending an S (SYN) flag.
Frame 3 - PPP-Blinky at IP 172.10.10.2 responds with an ACK in frame 3. One direction of the link is now established.
Frame 4 - The PC acknowledges the SYN sent by PPP-Blinky in frame 3. The TCP link is now fully established.
Frame 5 - The browser "pushes" (P flag is set) an HTTP GET request to PPP-Blinky.
Frame 6 - PPP-Blinky responds with a standard HTTP response "pushes" (P flag set) back a small web page. It also sets the A (ACK) flag to acknowledge the message sent in frame 6.
Frame 7 - The PC acknowledges reception of the HTTP payload.
Frame 8 - The PC starts to shut down the TCP connection by sending a FIN flag.
Frame 9 - PPP-Blinky acknowledges the FIN request - the connection is now closed in one direction. It also sets a FIN flag in the response to request closure of the opposite direction of the connection.
Frame 10 - The PC acknowledges the FIN request. The closing of the TCP connection is now confirmed in both directions.

/media/uploads/nixnax/ms-network-monitor-http-get-1.gif

Debug Output

PPP-Blinky can output handy debug information to an optional second serial port.
The image below shows the debug output (Ident, Source, Destination, TCP Flags) for a complete HTTP conversation.
The PC messages are displayed in black. PPP-Blinky messages are blue.
Notice how PPP-blinky automatically inserts a blank line after each full HTTP conversation.

/media/uploads/nixnax/tcp-data-3.gif

Creating a Dial-Up Connection in Linux

The screen below shows the required pppd command to connect to PPP-Blinky from a Linux machine. This was much simpler than Windows! The USB serial port of the mbed LPC1768 board registered as /dev/ttyACM0 on my Linux box. Do a websearch on pppd if you want to learn more about pppd, the Linux PPP handler. Near the bottom of the screen below, two webpages are fetched (/ and /y) by using the curl command on the command line. Gnome Webkit and Firefox work fine, too. Also try echo GET / HTTP/1.1 | nc 172.10.10.2 which uses netcat, the "Swiss army knife" of networking tools. PPP-Blinky was also tested with ApacheBench, the Apache server benchmark software. After 100000 fetches, the mean page fetch rate was reported as 6 page fetches per second for a small page.

/media/uploads/nixnax/pppd-screen.png

Caveats

PPP Blinky is an extremely sparse implementation (1.5k lines) of HTTP,WebSocket,TCP, UDP, ICMP, IPCP and LCP over PPP, requiring around 8kB of RAM. The minimum functionality required to establish connectivity is implemented. These are often acceptable tradeoffs for embedded projects as well as a handy tool to learn the practical details of everyday networking implementations.

main.cpp@4:a469050d5b80, 2016-12-29 (annotated)

Committer:
nixnax
Date:
Thu Dec 29 04:21:29 2016 +0000
Revision:
4:a469050d5b80
Parent:
3:bcc66de0bdcd
Child:
5:27624c02189f
PPP link is working; Receiving IPCP packet

Who changed what in which revision?

UserRevisionLine numberNew contents of line
nixnax 0:2cf4880c312a 1 #include "mbed.h"
nixnax 0:2cf4880c312a 2
nixnax 0:2cf4880c312a 3 // Proof-of-concept for TCP/IP using Windows 7/8/10 Dial Up Networking over MBED USB Virtual COM Port
nixnax 0:2cf4880c312a 4
nixnax 4:a469050d5b80 5 // Toggles LED1 every time the PC sends an IP packet over the PPP link
nixnax 4:a469050d5b80 6
nixnax 4:a469050d5b80 7 // Note - turn off all authentication, passwords, compression etc. Simplest link possible.
nixnax 0:2cf4880c312a 8
nixnax 0:2cf4880c312a 9 Serial pc(USBTX, USBRX); // The USB com port - Set this up as a Dial-Up Modem
nixnax 4:a469050d5b80 10 Serial xx(PC_10, PC_11); // debug port - use a second USB serial port to monitor
nixnax 0:2cf4880c312a 11
nixnax 4:a469050d5b80 12 DigitalOut led1(LED1);
nixnax 4:a469050d5b80 13
nixnax 4:a469050d5b80 14 #define FRAME_7E (0x7e)
nixnax 4:a469050d5b80 15 #define BUFLEN (1<<14)
nixnax 4:a469050d5b80 16 char rxbuf[BUFLEN];
nixnax 4:a469050d5b80 17 char frbuf[3000]; // buffer for ppp frame
nixnax 0:2cf4880c312a 18
nixnax 4:a469050d5b80 19 struct {
nixnax 4:a469050d5b80 20 int online;
nixnax 4:a469050d5b80 21 struct {
nixnax 4:a469050d5b80 22 char * buf;
nixnax 4:a469050d5b80 23 int head;
nixnax 4:a469050d5b80 24 int tail;
nixnax 4:a469050d5b80 25 } rx; // serial port buffer
nixnax 4:a469050d5b80 26 struct {
nixnax 4:a469050d5b80 27 int len;
nixnax 4:a469050d5b80 28 int crc;
nixnax 4:a469050d5b80 29 char * buf;
nixnax 4:a469050d5b80 30 } pkt; // ppp buffer
nixnax 4:a469050d5b80 31 } ppp;
nixnax 0:2cf4880c312a 32
nixnax 4:a469050d5b80 33 void pppInitStruct(){ ppp.online=0; ppp.rx.buf=rxbuf; ppp.rx.tail=0; ppp.rx.head=0; ppp.pkt.buf=frbuf; ppp.pkt.len=0;}
nixnax 4:a469050d5b80 34
nixnax 4:a469050d5b80 35 int crcG; // frame check sequence (CRC) holder
nixnax 4:a469050d5b80 36 void crcDo(int x){for (int i=0;i<8;i++){crcG=((crcG&1)^(x&1))?(crcG>>1)^0x8408:crcG>>1;x>>=1;}} // crc calculator
nixnax 4:a469050d5b80 37 void crcReset(){crcG=0xffff;} // crc restart
nixnax 0:2cf4880c312a 38
nixnax 0:2cf4880c312a 39 void rxHandler() // serial port receive interrupt handler
nixnax 0:2cf4880c312a 40 {
nixnax 4:a469050d5b80 41 ppp.rx.buf[ppp.rx.head]=pc.getc(); // insert in buffer
nixnax 0:2cf4880c312a 42 __disable_irq();
nixnax 4:a469050d5b80 43 ppp.rx.head=(ppp.rx.head+1)&(BUFLEN-1);
nixnax 0:2cf4880c312a 44 __enable_irq();
nixnax 0:2cf4880c312a 45 }
nixnax 0:2cf4880c312a 46
nixnax 0:2cf4880c312a 47 int pc_readable() // check if buffer has data
nixnax 0:2cf4880c312a 48 {
nixnax 4:a469050d5b80 49 return (ppp.rx.head==ppp.rx.tail) ? 0 : 1 ;
nixnax 0:2cf4880c312a 50 }
nixnax 0:2cf4880c312a 51
nixnax 0:2cf4880c312a 52 int pc_getBuf() // get one character from the buffer
nixnax 0:2cf4880c312a 53 {
nixnax 0:2cf4880c312a 54 if (pc_readable()) {
nixnax 4:a469050d5b80 55 int x = ppp.rx.buf[ ppp.rx.tail ];
nixnax 4:a469050d5b80 56 ppp.rx.tail=(ppp.rx.tail+1)&(BUFLEN-1);
nixnax 0:2cf4880c312a 57 return x;
nixnax 0:2cf4880c312a 58 }
nixnax 0:2cf4880c312a 59 return -1;
nixnax 0:2cf4880c312a 60 }
nixnax 0:2cf4880c312a 61
nixnax 4:a469050d5b80 62
nixnax 4:a469050d5b80 63 void scanForConnectString(); // scan for connect attempts from pc
nixnax 1:9e03798d4367 64
nixnax 0:2cf4880c312a 65 int main()
nixnax 0:2cf4880c312a 66 {
nixnax 0:2cf4880c312a 67 pc.baud(115200);
nixnax 4:a469050d5b80 68 xx.baud(115200);
nixnax 4:a469050d5b80 69 xx.puts("\x1b[2J\x1b[H"); // VT100 terminal control code for screen clear/home
nixnax 4:a469050d5b80 70
nixnax 4:a469050d5b80 71 pppInitStruct(); // structure containing all the PPP stuff
nixnax 4:a469050d5b80 72
nixnax 0:2cf4880c312a 73 pc.attach(&rxHandler,Serial::RxIrq); // activate the receive interrupt handler
nixnax 4:a469050d5b80 74
nixnax 4:a469050d5b80 75 int frameStartIndex, frameEndIndex;
nixnax 4:a469050d5b80 76 int frameBusy=0;
nixnax 4:a469050d5b80 77
nixnax 0:2cf4880c312a 78 while(1) {
nixnax 0:2cf4880c312a 79 while ( pc_readable() ) {
nixnax 1:9e03798d4367 80 int rx = pc_getBuf();
nixnax 4:a469050d5b80 81 if (frameBusy) {
nixnax 4:a469050d5b80 82 if (rx==FRAME_7E) {
nixnax 4:a469050d5b80 83 frameBusy=0; // done gathering frame
nixnax 4:a469050d5b80 84 frameEndIndex=ppp.rx.tail-1; // remember where frame ends
nixnax 4:a469050d5b80 85 void processFrame(int start, int end); // process a received frame
nixnax 4:a469050d5b80 86 processFrame(frameStartIndex, frameEndIndex);
nixnax 4:a469050d5b80 87 }
nixnax 4:a469050d5b80 88 }
nixnax 4:a469050d5b80 89 else {
nixnax 4:a469050d5b80 90 if (rx==FRAME_7E) {
nixnax 4:a469050d5b80 91 frameBusy=1; // start gathering frame
nixnax 4:a469050d5b80 92 frameStartIndex=ppp.rx.tail; // remember where frame starts
nixnax 4:a469050d5b80 93 }
nixnax 0:2cf4880c312a 94 }
nixnax 4:a469050d5b80 95 }
nixnax 4:a469050d5b80 96 if (ppp.online==0) scanForConnectString(); // try to connect
nixnax 4:a469050d5b80 97 }
nixnax 4:a469050d5b80 98 }
nixnax 4:a469050d5b80 99
nixnax 4:a469050d5b80 100 void processFrame(int start, int end) {
nixnax 4:a469050d5b80 101 crcReset();
nixnax 4:a469050d5b80 102 char * dest = ppp.pkt.buf;
nixnax 4:a469050d5b80 103 ppp.pkt.len=0;
nixnax 4:a469050d5b80 104 int special=0;
nixnax 4:a469050d5b80 105 for (int i=start; i<end; i++) {
nixnax 4:a469050d5b80 106 if (special==0) {
nixnax 4:a469050d5b80 107 if (rxbuf[i]==0x7d) special=1;
nixnax 4:a469050d5b80 108 else { *dest++ = rxbuf[i]; ppp.pkt.len++; crcDo(rxbuf[i]);}
nixnax 4:a469050d5b80 109 } else {
nixnax 4:a469050d5b80 110 *dest++ = rxbuf[i]-32; ppp.pkt.len++; crcDo(rxbuf[i]-32);
nixnax 4:a469050d5b80 111 special=0;
nixnax 0:2cf4880c312a 112 }
nixnax 0:2cf4880c312a 113 }
nixnax 4:a469050d5b80 114 ppp.pkt.crc = crcG;
nixnax 4:a469050d5b80 115 ppp.rx.head=0; // reuse rxbuf
nixnax 4:a469050d5b80 116 ppp.rx.tail=0; // reuse rxbuf
nixnax 4:a469050d5b80 117 void determinePacketType(); // declare early
nixnax 4:a469050d5b80 118 determinePacketType();
nixnax 0:2cf4880c312a 119 }
nixnax 4:a469050d5b80 120
nixnax 4:a469050d5b80 121 void sendFrame(){
nixnax 4:a469050d5b80 122 crcReset(); for(int i=0;i<ppp.pkt.len-2;i++) crcDo(ppp.pkt.buf[i]);
nixnax 4:a469050d5b80 123 ppp.pkt.buf[ ppp.pkt.len-2 ] = ((~crcG)>>0)&0xff; // update crc lo
nixnax 4:a469050d5b80 124 ppp.pkt.buf[ ppp.pkt.len-1 ] = ((~crcG)>>8)&0xff; // update crc hi
nixnax 4:a469050d5b80 125 pc.putc(0x7e);
nixnax 4:a469050d5b80 126 for(int i=0;i<ppp.pkt.len;i++) {
nixnax 4:a469050d5b80 127 unsigned int cc = (unsigned int)ppp.pkt.buf[i];
nixnax 4:a469050d5b80 128 if (cc>32) pc.putc(cc);
nixnax 4:a469050d5b80 129 else {
nixnax 4:a469050d5b80 130 pc.putc(0x7d); pc.putc(cc+32);
nixnax 4:a469050d5b80 131 }
nixnax 4:a469050d5b80 132 }
nixnax 4:a469050d5b80 133 pc.putc(0x7e);
nixnax 4:a469050d5b80 134 }
nixnax 4:a469050d5b80 135
nixnax 4:a469050d5b80 136 void LCPrequestFrame() {
nixnax 4:a469050d5b80 137 ppp.pkt.buf[4]=2; // change to an ACK packet
nixnax 4:a469050d5b80 138 sendFrame(); // return their request
nixnax 4:a469050d5b80 139 ppp.pkt.buf[4]=1; // change back to a request
nixnax 4:a469050d5b80 140 ppp.pkt.buf[5] = ppp.pkt.buf[5]+1; // take the next id
nixnax 4:a469050d5b80 141 ppp.pkt.buf[16] = ppp.pkt.buf[16] ^ 0x33; // modify magic number
nixnax 4:a469050d5b80 142 ppp.pkt.buf[17] = ppp.pkt.buf[16] ^ 0x33; // modify magic number
nixnax 4:a469050d5b80 143 sendFrame(); // send our request
nixnax 4:a469050d5b80 144 }
nixnax 4:a469050d5b80 145
nixnax 4:a469050d5b80 146 void LCPackFrame() {
nixnax 4:a469050d5b80 147 xx.printf("== PPP is up ==\n");
nixnax 4:a469050d5b80 148 }
nixnax 4:a469050d5b80 149
nixnax 4:a469050d5b80 150 void generalFrame() {
nixnax 4:a469050d5b80 151 xx.printf("== General Frame ==\n");
nixnax 4:a469050d5b80 152 for(int i=0;i<ppp.pkt.len;i++) xx.printf("%02x ", ppp.pkt.buf[i]);
nixnax 4:a469050d5b80 153 xx.printf(" C %02x %02x L=%d\n", ppp.pkt.crc&0xff, (ppp.pkt.crc>>8)&0xff, ppp.pkt.len);
nixnax 4:a469050d5b80 154 }
nixnax 4:a469050d5b80 155
nixnax 4:a469050d5b80 156 void iPcpFrame() {
nixnax 4:a469050d5b80 157 xx.printf("== IPCP Frame ==\n");
nixnax 4:a469050d5b80 158 for(int i=0;i<ppp.pkt.len;i++) xx.printf("%02x ", ppp.pkt.buf[i]);
nixnax 4:a469050d5b80 159 xx.printf(" C %02x %02x L=%d\n", ppp.pkt.crc&0xff, (ppp.pkt.crc>>8)&0xff, ppp.pkt.len);
nixnax 4:a469050d5b80 160 led1 = ppp.pkt.buf[3] & 1; // This is the sequence number so the led blinks on packets
nixnax 4:a469050d5b80 161 }
nixnax 4:a469050d5b80 162
nixnax 4:a469050d5b80 163 void determinePacketType() {
nixnax 4:a469050d5b80 164 char pktLCPReqType [] = { 0xff, 3, 0xc0, 0x21, 1 }; // LCP requeswt packet
nixnax 4:a469050d5b80 165 char pktLCPAckType [] = { 0xff, 3, 0xc0, 0x21, 2 }; // LCP ack packet
nixnax 4:a469050d5b80 166 char pktIPCPtype [] = { 0x80, 0x21, 1 }; // ip control packet
nixnax 4:a469050d5b80 167 if(0);
nixnax 4:a469050d5b80 168 else if (0==memcmp( ppp.pkt.buf,pktLCPReqType,5)) LCPrequestFrame();
nixnax 4:a469050d5b80 169 else if (0==memcmp( ppp.pkt.buf,pktLCPAckType,5)) LCPackFrame();
nixnax 4:a469050d5b80 170 else if (0==memcmp( ppp.pkt.buf,pktIPCPtype,3 )) iPcpFrame();
nixnax 4:a469050d5b80 171 else generalFrame(); // default handler
nixnax 4:a469050d5b80 172 }
nixnax 4:a469050d5b80 173
nixnax 4:a469050d5b80 174 void scanForConnectString(){
nixnax 4:a469050d5b80 175 char * clientFound = strstr( rxbuf, "CLIENTCLIENT" ); // look for PC string
nixnax 4:a469050d5b80 176 if( clientFound ) {
nixnax 4:a469050d5b80 177 strcpy( clientFound, "FOUND!FOUND!" ); // overwrite so we don't get fixated
nixnax 4:a469050d5b80 178 pc.printf("CLIENTSERVER"); // respond to PC
nixnax 4:a469050d5b80 179 }
nixnax 4:a469050d5b80 180 }