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Application Report

SLAA137A – February 2004

MSP430 Internet Connectivity

Andreas Dannenberg MSP430

ABSTRACT

Computer communication systems and especially the Internet are playing a rapidly

increasingly important role in our everyday environment. But today this is not only a

domain of personal computers or workstations. More and more, it makes its way to

smaller network nodes, too. Imagine applications that are able to control hardware via a

standard Internet browser, to transmit and visualize the state of sensors or automatically

generate and send E-mails on the occurrence of special events (for example, for security

purposes).

This application report describes in detail the implementation of an embedded Web server

based on the MSP430 ultralow-power microcontroller series from Texas Instruments. The

solution consists of both hardware (schematic, parts list) and software (C source). An

ethernet LAN controller offers the physical connection to the Internet. A downsized

TCP/IP protocol stack is used. Its functionality is encapsulated by an easy-to-use

application programming interface (API). By using this API, creating new applications or

modifying existing ones becomes an easy task. As an application example, a dynamic

HTTP server is implemented.

Contents

1 Introduction........................................................................................................................................3

2 Important Protocol Basics................................................................................................................3

2.1 Ethernet........................................................................................................................................4

2.2 Address Resolution Protocol .......................................................................................................5

2.3 Internet Protocol...........................................................................................................................5

2.4 Internet Control Message Protocol..............................................................................................6

2.5 Transmission Control Protocol ....................................................................................................6

2.6 Hypertext Transfer Protocol.........................................................................................................7

3 Hardware Description........................................................................................................................7

3.1 Interfacing to the LAN Controller .................................................................................................8

3.2 Circuit Description........................................................................................................................9

3.3 Connection to the Network ........................................................................................................10

4 Software Description.......................................................................................................................11

Amiga is a trademark of Amiga, Inc.

Apple and Macintosh are trademarks of Apple Computer, Inc.

Athlon is a trademark of Advanced Micro Devices, Inc.

Cassiopeia is a trademark of Casio Keisanki Kabushiki Kaisha DBA Casio Computer Co., Ltd., Japan

Crystal is a trademark of Crystal Semiconductor Corporation.

Cirrus is a trademark of Cirrus Logic, Inc.

Microsoft and Internet Explorer are a trademarks of Microsoft Corporation.

Netmon is a trademark of Systems Enhancement Corporation.

Netscape Navigator is a trademark of Netscape Communications Corporation.

Open Transport is a trademark of Information Management Company.

Pentium is a trademark of Intel Corporation.

Other trademarks are the property of their respective owners.

ZIP file: http://www.ti.com/lit/zip/slaa137

Summary of content (32 pages)

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Application Report SLAA137A – February 2004 MSP430 Internet Connectivity Andreas Dannenberg MSP430 ABSTRACT Computer communication systems and especially the Internet are playing a rapidly increasingly important role in our everyday environment. But today this is not only a domain of personal computers or workstations. More and more, it makes its way to smaller network nodes, too.
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SLAA137A 4.1 Ethernet Module .......................................................................................................................... 4 4.2 TCP/IP Module ............................................................................................................................ 4 4.2.1 Buffer Memory................................................................................................................. 4 4.2.2 Global Variables .......................................................
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SLAA137A 1 Introduction While known for its use in PC networks, the ethernet also offers a robust, well-understood and reasonably priced technology for networking applications beyond the desktop computer. The goal of this design is to show how easy it is to implement a TCP/IP stack as well as an ethernet interface for the MSP430. It provides both a source code for the programmer as well as schematics for the design engineer.
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SLAA137A Table 1. Layer Name Application layer Transport layer Internet layer Network layer Functions of Internet Reference Model Layers Function Contains a lot of protocols defined by different applications to provide their services. Makes the communication between endpoints possible. Delivery and routing of datagrams between Internet nodes. Host-specific implementation of transmission of datagrams.
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SLAA137A Every network node has its own unique physical address. It is 48 bits long and called the media access control (MAC) address. The maximum length possible for an Ethernet frame is 1518 bytes. This size covers the whole frame, excluding the preamble. The preamble consists of alternating zeros and ones and is used for synchronization purposes. It is followed by the real frame. The first 48 bits are the destination and the second 48 bits are the source MAC address.
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SLAA137A 2.4 Internet Control Message Protocol The internet control message protocol (ICMP) provides a mechanism for reporting problems and generating diagnostic messages, e.g., when a datagram cannot reach its destination, when a gateway does not have the buffering capacity to forward a datagram, or when the gateway recommends a shorter route. Thus the datagram service can achieve a better communication reliability. The ICMP uses the basic support of IP. However, it is an integral part of the IP layer.
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SLAA137A 2.6 Hypertext Transfer Protocol The hypertext transfer protocol (HTTP) is an application level protocol. It is a generic, stateless, object oriented protocol that can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods (commands). It uses a client-server relationship and is based on a stream-oriented transport layer, such as TCP.
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SLAA137A 8 MHz 20 MHz D[7..0] JTAG MSP430F149 A[3..0] CS8900A IOR IOW Isolation Transformer LEDs: Power, Link, LAN RJ45 Connector Figure 3. 3.1 Hardware Block Diagram Interfacing to the LAN Controller The most interesting thing is the connection between the LAN controller (IC2) and the MCU (IC1). The CS8900A can operate in three different modes: I/O space, memory space, and as a DMA slave. All of these modes have their special advantages and disadvantages.
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SLAA137A 3.2 Circuit Description The analog circuitry around the CS8900A is built as further described in Resource [8]. A 20-MHz crystal is connected between the pins XTAL1 (pin 97) and XTAL2 (pin 98) of the CS8900A. Because of the built-in loading capacitance on the XTAL pins, no external capacitors are needed. The power-on reset signal is generated by the R/C combination R9/C17. The LAN controller, other than the MSP430, needs an active-high reset signal.
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SLAA137A Figure 4. Prototype Board With Components Installed Appendix A shows the schematic and Appendix B provides a list of components that are needed to build the module. For each of the discrete parts, there are several manufacturers available. 3.3 Connection to the Network The CS8900A includes an integrated 10Base-T transceiver. It contains all the analog and digital circuitry needed for implementing the LAN interface by the use of a simple isolation transformer (IND1).
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SLAA137A 4 Software Description This chapter describes the implemented TCP/IP stack, the ethernet driver, and the HTTP server. The entire software is written in C and therefore porting to other MCU systems should be quite easy. For reasons of better understanding, the code is separated into different modules. Table 3 gives an overview of these modules. Table 3. Application Overview of the Software Modules • Transfers data via ethernet and TCP/IP • TCP/IP module (tcpip.c, tcpip.
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SLAA137A Table 4.
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SLAA137A Init8900() User Program Write8900(ADD_PORT, PP_RxEvent) (Read8900(DATA_PORT) & RX_OK)? Yes CopyFromFrame8900(...) No Yes Application Wants to Send Data? RequestSend(FrameSize) No Rdy4Tx()? No Yes RequestSend(FrameSize) Figure 5. 4.2 Using the Ethernet Module TCP/IP Module This software module represents the most important part of the demonstration board because the protocols for transferring data over a TCP/IP connection are implemented here.
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SLAA137A • A time-out is exceeded • An error occurs (network error, connection is reset by the opponent) The software implements the essential parts of the standards RFC 791, 792 and 793. The most important function of this stack is DoNetworkStuff(). This function must be called periodically by the user application. The event handling of the TCP is done here. Different flags are polled in both the ethernet controller and the MCU.
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SLAA137A 4.2.1 Buffer Memory To work with incoming and outgoing frames, three memory buffers are reserved in the MCU SRAM. The size of these buffers can be adapted by changing the appropriate symbolic constants in tcpip.h. Increasing the size of the buffers leads to a dramatic increase of the transfer speed, because the demonstration software maintains only one buffer for sending and one buffer for transmitting data over TCP/IP.
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SLAA137A Frame Was Received. Individually Addressed? Broadcast? ARP, Opcode REPLY? IP? Process Frame. ICMP? TCP? ProcessICMPFrame() ProcessTCPFrame() Figure 8. Demultiplexing of Received Frames If the frame was individually addressed, it is first checked to determine if it is an ARP answer frame for a previously sent ARP request of the local TCP. In this case, the opponent’s MAC address is extracted. This mechanism is used for performing an active open of a connection.
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SLAA137A To prevent the receive buffer from corruption while receiving data, a handshake mechanism is implemented. This mechanism uses the SOCK_DATA_AVAILABLE flag of the SocketStatus register. The TCP stack only copies data to RxTCPBuffer if the SOCK_DATA_ AVAILABLE flag is clear, and only in this case is an ACK-segment sent back to the other TCP. If the RxTCPBuffer is empty and the stack has written new data to it, this is indicated to the application by setting the SOCK_DATA_AVAILABLE flag.
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SLAA137A 4.2.6 Closing a Connection A TCP connection can be closed on different events. Normally this is done either locally by calling the user function TCPClose() or remotely by the other TCP. During the termination of a connection, segments carrying FIN flags are exchanged. If the retransmission counter exceeds a limit or a segment with a RST (reset) flag is received, the connection is also closed. This is an error situation that is indicated by an error code in the SocketStatus register. 4.2.
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SLAA137A Table 5. Compatible Communication Systems Computer System / CPU PC / Athlon™/ 1 GHz Operating System, TCP/IP Stack Windows 2000 PC / Athlon / 1 GHz PC / Pentium™ / 233 MHz Linux, kernel v 2.2.16 Windows 98 PC / 486DX2 / 66 MHz Apple™ Macintosh™ / 68030 / 50 MHz Windows 95 System 7.5, Open Transport™ 1.1.2 AT Amiga™ / 68030 / 50 MHz Cassiopeia™ / MIPS / 150 MHz Kickstart 3.0, Miami 2.1 Windows CE 3.
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SLAA137A Very important for the proper function of the stack is the periodic calling of the function DoNetworkStuff() by the application. A typical program flow chart using this TCP/IP API is shown in Figure 9. DoNetworkStuff() Open or Close Connection Process Incoming or Outgoing Data Misc Program Misc Program No Termination of Program Requested? Yes Figure 9.
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SLAA137A 4.3.1 Functions void TCPLowLevelInit(void) This function does a basic setup of the ethernet controller and numerous variables; it also configures ports and timer_A of MSP430. It must be called before any data transmission via TCP/IP can take place. void TCPPassiveOpen(void) By calling this function, the stack switches to the server mode to detect an incoming connection. The flag SOCK_ACTIVE is set indicating the stack is busy now.
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SLAA137A void TCPClose(void) Use this API function to close an open connection. Before disconnecting, the stack ensures that a packet that still resides in the output buffer is transmitted and acknowledged properly. After closing, the application may reconfigure IP addresses, reassign port numbers, and open a new connection.
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SLAA137A Bit 7 SOCK_ ERROR Bit 6 SOCK_ ERROR Bit 5 SOCK_ ERROR Bit 4 SOCK_ ERROR Bit 3 SOCK_TX_BUF_ RELEASED Bit 2 SOCK_DATA_ AVAILABLE Bit 1 SOCK_ CONNECTED Bit 0 SOCK_ ACTIVE Figure 11. SocketStatus Register SOCK_ACTIVE (Bit 0) This flag is set when the TCP is busy opening a connection (previous call of an API method to open a session). While set, no further call of one of these functions is allowed. If an open fails or the connection is closed normally, the stack clears this flag again.
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SLAA137A SOCK_TX_BUF_RELEASED (Bit 3) This flag indicates whether the application can change the contents of the transmit buffer or modify the TCPTxDataCount variable. This flag is set by the stack if the previous packet sent was acknowledged properly. This realizes a kind of handshake mechanism to protect the transmit buffer from overwriting its contents. For the common way of sending data, see description of the function TCPTransmitTxBuffer().
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SLAA137A Initalizing of Clock System Configure MCU's I/O Ports TCPLowLevelInit() Initialize HTTP Server's Flag-Register TCPLocalPort = TCP_PORT_HTTP No SOCK_ACTIVE? TCPPassiveOpen() Yes DoNetworkStuff() HTTPServer() Figure 13.
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SLAA137A After initializing some hardware and the stack itself, the local TCP port is set to 80 (default for an HTTP server). The server is now waiting for a client to be connected. During the first jump to HTTPServer() after connecting, the flag HTTP_SEND_PAGE in register HTTPStatus is clear. It is used to process some special code sections during this first execution of HTTPServer(). The web server checks for any incoming TCP data and discards it.
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SLAA137A easyWEB - dynamic Webside
Hello World!

This is a dynamic webside hosted by the embedded Webserver easyWEB.

Hardware:
- MSP430F149, 8 MHz, 60KB Flash, 2KB SRAM
- CS8900A Crystal Ethernet Controller
A/D Converter Value Port P6.

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SLAA137A By using the REFRESH statement in the HEAD section of the page’s source code, an Internet browser can be advised to reload the page after a specified timeout period. In the demonstration HTTP server, the page is reloaded each five seconds. The HTML code shown is compatible with all common Internet browsers (such as Microsoft Internet Explorer™, Netscape Navigator™).

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SLAA137A 5 References 1. TCP/IP Running a Successful Network by Washburn, K., Evans, J. Addison Wesley, 1996 2. Internet Protocol (IP) by Postel, J., RFC 791† 3. Internet Control Message Protocol by Postel, J., RFC 792† 4. Transmission Control Protocol by Postel, J., RFC 793† 5. An Ethernet Address Resolution Protocol by Plummer, D., RFC 826† 6. Requirements for Internet Hosts by Braden, R., RFC 1122† 7. MSP430x13x, MSP430x14x Mixed Signal Microcontroller Data Sheet (SLAS272) 8. CS8900A Product Data Sheet.

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SLAA137A Appendix A.

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SLAA137A Appendix B. Parts List Part Name Value / Description 560 pF Package SMT 0805 C2, C3, C6, C13, C14, C15, C16, C17, C18, C19, C20, C21, C22 C4, C5 0.

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