Ethernet Module

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This project aims to develop an Ethernet Module, to be used in conjunction with a 8/16 bits embedded system such as the dsPic33F development board.

Contents

Objectives

The Internet provides an indispensable means to exchange information over long distances. Connection to the Internet is enabled by following the implementation of the Open Systems Interconnection Reference Model (OSI model). In simple words, internet applications require a TCP/IP stack to pack and unpack information into data packets for proper transmission and reception over the Internet. The TCP/IP stack is usually implemented by software and included in the Operating System. Applications can use the stack transparently through socket programming.

Since a full-scale TCP/IP stack consumes a large amount of memory and processing power, a number of small footprint TCP/IP stacks have been devised for embedded systems, such as uIP and lwIP. Nevertheless, these TCP/IP stacks are usually not compatible to socket programming, and being implemented by software, still consumes a considerable amount of system resources. Therefore, hardware chips that implemented the TCP/IP stack (e.g. WIZNET W5300) emerged in recent years so as to offload the computation power from the host microcontroller unit (MCU).

This project aims to devise a driver and Linux socket wrapper inside freertos_posix for a hardware implemented TCP/IP stack. It is to be used in conjunction with a 8/16 bits embedded system such as (but not restricted to) the dsPic33F development board. Based on the Linux socket API, common application protocols (DHCP/HTTP/DNS/SMTP/SNMP/TELNET) are devised to enable remote control and monitoring.

Benefits

  • Provide a means to perform remote control and monitoring via Internet
  • Offload TCP/IP stack to chip, freeing memory and processing power of MCU to perform other tasks (e.g. HTTPS)
  • Socket API implementation allows more extensible framework for future development and upgrades
  • Enable remote control and monitoring via
    • Web browser on desktop computer (better web page design and implementation)
    • SNMP agents, controlling and monitoring several instruments simultaneously
    • TELNET applications for command prompt control and monitoring
    • SMTP by sending out email when critical events occur

Limitations

  • Higher cost chips compare to software stack
  • Need to change hardware if features in stack are updated


Architecture

  • See here for block diagram


Development Roadmap

Phase 1

  • Select chips and draw schematic and pcb
  • Obtain samples for chip

Phase 2

  • Device driver
  • Create a Linux socket API wrapper in freertos_posix

Phase 3

  • Reference to Linux socket/lwip, create libraries for
    • DHCP client
    • HTTP server
      • Decide how to get files (html, css, cgi, etc) from nvm (with/without file system)
      • Decide an efficient means to create and download web page to nvm
    • DNS resolver
    • SMTP mail client
    • SNMP agent
    • TELNET application

Phase 4

Using TCP-IP Remote Control Interface

Network Configuration

Our Ethernet products (units) can be controlled by a PC using the TCP-IP protocol. The PC and the units can be setup using one of three topologies: (i) Direct Connection; (ii) Intranet Connection; (iii) Internet Connection.

Direct Connection

An example showing how to connect a PC and a unit directly is shown in Fig. 1. In this topology, the unit can be connected with the PC simply using a direct Ethernet cable. Please ensure that the PC and the unit share the same subnet mask and gateway, but different IP addresses. An incorrect example is shown in Fig. 2. Under direct connection, the user has to set these network configurations manually.

  • Correct network setting.png
  • Incorrect network setting.png

To set the network configuration on the unit, the user has to select the Static mode. The default IP addresses, subnet mask, and gateway are 192.168.1.128, 255.255.255.0 and 192.168.1.1 respectively. These settings can only be changed when the Ethernet status is Down. Once they have been changed, the values will be automatically saved.

To configure the network settings on the PC,

  • Goto <Start> and <Control Panel>, open <Network Connections>

Networksetting1.png

  • Select the Local Area Connection corresponding to the network card on your PC. Right click and select <Properties>

Networksetting2.png

  • Under <General> tab, scroll down to <Internet Protocol (TCP/IP)> and click <Properties>

File:Networksetting3.png

  • Select <Use the following IP address:> and enter the appropriate network settings. Please ensure that the IP address is different from the one used by the unit.

File:Networksetting4.png

Connection Schemes

Connection schemes.png Connection schemes withdhcp.png

Software TCP/IP Stack Solution

Circuit and PCB

Special Item Description Quantity
DM9000AEP Ethernet Controller from Davicom 1
HR911102A RJ45 Connector with Integrated Magnetics for 10/100 Base-TX 1
93LC46B-I/SN 1K Serial EEPROM 1 (Optional)
25MHz Crystal Crystal 1
22pF For Crystal Use 2
220uF For RXVDD25/TXVDD25 1
49.9ohm For RX+/RX-/TX+/TX- 4
6.8kohm For BGRES/BGGND 1
510ohm For LEDs 2


Software Implementation

Driver

  • Download dm9000a.c
  • Download dm9000a.h
  • Base on FreeRTOS and dsPIC33 platform
  • Using POSIX-like API:
    • int dmfe_open(int flags): initialize the Ethernet controller for 10MHz Half-Duplex
    • int dmfe_close(): turn off the PHY layer
    • int dmfe_read(void): copy a packet to the default buffer
    • int dmfe_write(unsigned char device, unsigned char *buf, int count): copy count bytes of the data from buf and transmit
    • void dmfe_interrupt(void): process the transmit interrupt from DM9000A

uIP

  • Light-weight TCP/IP stack designed for 8-bit/16-bit embedded systems

lwIP

  • Light-weight TCP/IP stack designed for 8-bit/16-bit embedded systems
  • Consume more resource than uIP


Hardware TCP/IP Stack Solution

Circuit and PCB

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