Application Note
AN_408
FT90x Telnet to UART Bridge
Version 1.0
Issue Date: 2016-04-27
This application note describes an Ethernet to serial bus (UART) implemented
on the FT90x. It uses the telnet protocol for transferring data between the
serial bus and a remote network client and an HTTP configuration interface.
Use of FTDI devices in life support and/or safety applications is entirely at the user’s risk, and the
user agrees to defend, indemnify and hold FTDI harmless from any and all damages, claims, suits
or expense resulting from such use.
Future Technology Devices International Limited (FTDI)
Unit 1, 2 Seaward Place, Glasgow G41 1HH, United Kingdom
Tel.: +44 (0) 141 429 2777 Fax: + 44 (0) 141 429 2758
Web Site: http://ftdichip.com
Copyright © Future Technology Devices International Limited
Application Note
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Table of Contents
1 Introduction ............................................................ 3
1.1 Overview.......................................................................... 3
1.2 Scope ............................................................................... 3
1.2.1
Features ........................................................................................ 3
1.2.2
Enhancement.................................................................................. 3
2 Project Overview ..................................................... 4
2.1 Main Program ................................................................... 4
2.2 Network Code................................................................... 4
2.2.1
Network Abstraction......................................................................... 4
2.2.2
lwIP Library .................................................................................... 4
2.3 Telnet Code ...................................................................... 5
2.3.1
Telnet Abstraction ........................................................................... 5
2.3.2
Telnet Library ................................................................................. 5
2.4 Persistent Storage ............................................................ 5
2.5 Web Pages ....................................................................... 5
2.6 Other Features ................................................................. 6
3 Code Structure ........................................................ 7
4 Configuration ........................................................ 11
4.1 Default Configuration ..................................................... 11
4.1.1
Network........................................................................................ 12
4.1.2
UART............................................................................................ 12
4.2 Modifying the Configuration ............................................ 12
4.2.1
Telnet Client .................................................................................. 12
4.2.2
Network Conf iguration..................................................................... 13
4.2.3
Programming ................................................................................. 13
5 Performance.......................................................... 15
5.1 19200 baud .................................................................... 15
5.2 115200 baud .................................................................. 15
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6 Contact Information .............................................. 16
Appendix A – References ........................................... 17
Document References ............................................................ 17
Acronyms and Abbreviations .................................................. 17
Appendix B – List of Tables & Figures ......................... 18
List of Tables ......................................................................... 18
List of Figures ........................................................................ 18
Appendix C – Revision History .................................... 19
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1 Introduction
The FT900/FT901 and FT905/FT906 devices include an Ethernet interface. This can be used with a
suitable networking stack to allow the device to be networked. This application note shows how
the Ethernet interface can be used to bridge the built-in UART to a remote telnet client.
1.1 Overview
UART Bridge on the FT90x. Data transmitted to the bridge from the remote client is forwarded
onto the UART interface of the FT90x, data received on the UART is transmitted to the remote
client.
The network interface supports DHCP to obtain configuration information or it can be configured
using a web page served by the FT90x firmware. UART configuration is performed using the same
web page.
The configuration is stored in FlashROM on the device.
Third-party open source code is used to implement a TCP/IP stack and a telnet library in this
application note:
TCP/IP - lwIP (LightWeight IP) library which has been ported to the FT90x.
Telnet – libtelnet.
Printf – tinyprintf.
Links to resources for these libraries are in Appendix A – References.
1.2 Scope
The telnet protocol is widely used on LANs to provide bi-directional communications. It is not
encrypted or otherwise secured and is not generally used on open networks. Security concerns
have made the SSH protocol more widely used. This application note does not intend to provide
any encryption or security and as such should be deployed on private LANs where access is
controlled.
1.2.1 Features
The application note highlights the use of lwIP to provide a TCP/IP stack. The “arch” folder of lwIP
in the source code for the application note contains the architecture-specific parts of lwIP required
for the FT90x.
1.2.2 Enhancement
Enhancements to this application might be:
To implement SSH protocol instead of telnet.
To provide access to the UART through a web page.
Allow only permitted IP addresses to connect to the device.
Reduce the overall size of the application code .
This telnet to UART bridge example application should be treated as an example. Full source code
is provided allowing users to build and modify if required.
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2 Project Overview
The project files for this application note are divided into the following folders.
Folder
Description
Source
Application source code and abstraction files.
httpdfs
File system for web server.
lib
Library files.
lib\tinyprintf
tinyprintf library.
lib\libtelnet
Telnet library.
lib\lwip
lwIP library.
Table 2.1 Project Files Overview
The application source code is contained within the “Sources” folder. The main() function and the
high-level functions of the application are in the “main.c” file. In this folder there are 2 abstraction
files, one for the network interface (“net.c”) and another for the telnet library (“telnetd.c”).
2.1 Main Program
The main program is responsible for handling data between the UART interface and the telnet
library.
It also handles configuration by the web interface. The code generates data for the simple server
side includes (SSI) functions in the lwIP httpd server. Data is returned through HTTP GET requests
to update the configurations. The httpd server uses callbacks for both the server size includes and
HTTP GET handler.
The dlog features described in AN_365 FT900 API Programmers Manual are used for persistent
storage and retrieval of configuration data.
2.2 Network Code
The networking layer is provided by the lwIP library which has been ported to support the FT90x.
The lwIP code is available separately from FTDI with the FT90x architecture extensions.
2.2.1 Network Abstraction
The network interface is abstracted from the main project in the file “net.c”. All lwIP features
which refer to an interface (netif) are passed through this layer.
The lwIP network interface is initialized and configured using data supplied from the main
application. The function which processes incoming packets for the network interface within lwIP is
called from the net_tick() function.
2.2.2 lwIP Library
The library is available with a BSD-style license. A snapshot of the code from March 2016 is used
as the basis. No changes have been made to the code from the lwIP project page.
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The FT90x architecture code is responsible for obtaining packets from the Ethernet interface and
transmitting packets to the Ethernet interface.
The application makes extensive use of the callback me thods in lwIP to permit sending and
receiving of data.
The httpd app (which has been moved from contrib to the main lwIP code after V1.4.0) is used to
provide an interface for configuration. This makes use of server side includes (SSI) and CGI scripts
(HTTP GET requests) to present configuration data to the user and change it when requested to do
so.
2.3 Telnet Code
2.3.1 Telnet Abstraction
A small abstraction layer is used to interface libtelnet to the lwIP code. Several callback functions
are used to receive information from the libtelnet library which can be data or control messages.
Data is passed from this layer to the UART handler in the main application code or the network
interface in the lwIP code.
2.3.2 Telnet Library
The libtelnet library is used to interpret the in-band control codes and manage the telnet protocol.
This is public domain code. It is not modified for this application.
A minimum set of DO and DON’T requests and WILL and WON’T instructions are used. Terminal
settings to control the UART interface are not implemented, instead the configuration interface is
used.
2.4 Persistent Storage
Configuration parameters including the networking and UART parameters are stored in FlashROM
on the device. The 4 kB long datalogger partition is used to keep this data b etween power cycles.
The data is updated each time the data is changed by the configuration interface.
When the application starts it checks the data stored for the network and UART configuration in
the persistent storage. Two 32-bit keys are used (one for the network and one for the UART
sections) to ensure that the data read is valid. If one value is incorrect then default values are
loaded for that function.
When the FlashROM is reprogrammed by the FT90x Programming Utility it is normal for this data
to be overwritten. This will result in default parameters being used until the data is reprogrammed.
2.5 Web Pages
The configuration web pages are stored in a folder called httpdfs on the top level of the directory
structure for the project. The raw html and ima ge files are compiled into a single C file (fsdata.c)
which is included in the source code of the application. An internal library in the lwIP httpd code
reads this data and extracts files for the web service.
A batch file (makefs.bat) and a compilation utility (makefsdata.exe) Windows platforms are
included to perform the compilation and place the fsdata.c file in the correct place. Changes to the
web pages have to be compiled before the application is recompiled.
Further details on how lwIP performs Server Side Include (SSI) and acts on the HTTP GET requests
used to update the configuration are to be found in the lwIP documentation.
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2.6 Other Features
The DFU-C facility is enabled for this application. This is called from the macro STARTUP_DFU() in
the main() function. It will briefly enable the USB device on the FT90x and allow a DFU utility to
update the application code. This can be removed entirely or configured to alter the number of
milliseconds it will wait before closing the USB device a nd continuing with the application.
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3 Code Structure
The code is written to use the lwIP library efficiently. Callbacks are used to link the lwIP code to
the telnet abstraction layer and then to the telnet library.
Data sent via telnet is routed in both directions through the abstraction layer to the telnet library.
The main function “bridge()” polls the UART and sends any data received through the telnet library
(Figure 3.1). The telnet library processes the data to encapsulate it in the telnet protocol. When
this is complete a callback function in the abstraction layer routes the data to the lwIP library for
transmission (Figure 3.2).
In the other direction, data received from the network by the lwIP library is sent to the telnet
library for processing. Data is returned to the abstraction layer by a callback and is then sent back
to the main function for transmission over the UART (Figure 3.3).
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bridge()
Main loop.
uart_Rx()
Receive UART
data from
circular buffer.
net_tick()
Abstract lwIP.
wdt_kick()
Keep Watchdog
running.
sys_check_timeouts()
Update lwIP operations
in progress.
net_tick()
arch_ft900_tick()
lwIP library.
Figure 3.1 Main Function Flowchart
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uart_Rx()
telnetd_send()
UART
Input
No
C learance N o.: FT DI# 5 0 0
telnet_send()
Send through
libtelnet library.
data?
Callback
Yes
telnetd_send()
telnetd_event()
Send received data
to libtelnet.
No
SEND
Yes
tcp_write()
Send data to write
to lwIP.
Figure 3.2 UART to Telnet Function Flowchart
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telnetd_tcp_recv_cb()
arch_ft900_tick()
Ethernet
Input
No
No
data?
Ye
s
Callback
data?
C learance N o.: FT DI# 5 0 0
telnetd_process_recv ()
C onvert data received in
lwIP buffers.
Yes
Prepare
packets.
lwip input()
Process packets.
telnetd_process_recv ()
telnet_recv()
Callback
libtelnet library.
telnetd_event()
No
DATA
Callback
app_telnetd_receive_cb()
Yes
receive_cb()
Send received data
to main function.
uart_Tx()
Send received data
to UART.
Figure 3.3 Telnet to UART Function Flowchart
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4 Configuration
This section describes the default configuration used by the application and how to change the
configuration.
Figure 4.1 Web Configuration Interface
A web configuration page is accessible when the device connects to the network. This allows both
networking and UART settings to be altered.
In order to serve the configuration web page the device must be connected to the network and
have obtained (or have been configured with) an IP address. DHCP is enabled by default allowing
the application to request an IP address when it is firs t started.
In many cases it is possible to query the DHCP server on a network to find out the IP address
allocated to a particular device . In this application the device will send the DHCP server the
hostname “TelnetBridge” which some DHCP s ervers may make available to allow users to identify
the allocated address more easily.
Another way to obtain the IP address to access the web configuration page is to check the UART
debug text, while NET_DEBUG is defined in net.c, for example:
IP config:
ipaddr = 172.16.3.115
gwaddr = 172.16.2.5
netmask = 255.255.252.0
4.1 Default Configuration
A default MAC address is used by this application. It is set to 02:f7:d1:00:00:00 by default.
Note: This MUST be changed if more than one device is present on a network as MAC addresses
must be unique. The MAC address can be changed though the web configuration interface.
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4.1.1 Network
DHCP is turned on by default. The application will ask for an IP address, gateway and netmask
from any available DHCP server and use these values to configure the network interface. It will
also provide a hostname of “TelnetBridge” to the DHCP server.
4.1.2 UART
The following settings are used by default for the UART:
-
19200 baud
8 bits data
1 stop bit
no parity
There is no option for flow control at present.
4.2 Modifying the Configuration
The configuration web page is split into 3 sections:
-
a ‘Status’ section showing the IP address of a telnet client.
a ‘Network Configuration’ section.
a ‘UART Configuration’ section.
There are also shortcut links on the left to visit the FTDI web site, the FT90x section and the
support information within the FTDI website.
4.2.1 Telnet Client
This section provides the IP address of the telnet client connected to th e bridge. If no telnet client
is connected then it will display “Connected: No Connection”.
It is refreshed when the page is reloaded. The user can click on the Refresh button which is the
same as refreshing the webpage (F5).
It does not permit any configurable functionality.
A telnet client like PuTTY can be used for testing this application example , as shown in Figure 4.2.
Figure 4.2 PuTTY Telnet Client
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4.2.2 Network Configuration
The network configuration section has 2 sub-sections.
The first is the MAC address and hostname. These are required to be filled in for configuring the
device. As has been mentioned earlier the MAC address is required by Ethernet to be unique on a
network. This is the hardware address used for all low -level communications on Ethernet. A
network will act in an unspecified manner if this is duplicated.
It is recommended that bit 2 in the most significant byte (first octet transmitted) be set to 1 to
indicate that the MAC address is locally administered.
The hostname field is sent to the DHCP server during the DHCP negotiation and may be used by
the server to identify a device. In some DHCP setups it can be pass ed onto DNS to allow the
hostname to be used seamlessly within a local network.
The third network option is to enable or disable DHCP. When enabled this will instruct the
application to request an IP address, gateway address and netmask from a DHCP server. Therefore
the fields that configure these values are disabled. The values obtained from the server are shown
in the fields for information only.
If DHCP is disabled then the 3 fields are enabled allowing specific addresses to be configured.
There is no error checking that the values in the form are correctly formatted. The MAC address
MUST be 6 hexadecimal octets long with each octet separated by a colon. The IP address, gateway
and netmask are 4 decimal values separated by dots.
4.2.3 Programming
To program the Network Configuration and UART Configuration via the configuration webpage,
make edits as required then click on the ‘Apply’ button, then click on restart on the next page.
Note that the FT90x IC will be rebooted.
In Section 2.4 it is states that the configuration parameters are overwritten when programming
new code to the FlashROM. This is because the FT90x Programming Utility will write the entire
FlashROM when a new image is programmed. This will overwrite the datalogger partition with
blank formatting.
However, when using the FT90x Programming Utility to configure one or many devices, a “Config
File” can be specified and used to store preconfigured parameters into the datalogger partition.
The address of the partition will be 8 kB from the top of FlashROM (0x3E000).
An existing datalogger partition can be copied from an FT90x device using the “Data Log” tab in
the FT90x Programming Utility. The binary file obtained can be modified to change any of the
configurable parameters using the structs “net_config” and “uart_config” defined in the source
code.
The network config is at an offset of 0x100 in the datalogger file and the UART config is at offset
0x200. Both structures have a 32-bit signature field to validate the values stored. The first and
last 256 bytes of the datalogger file have required validation data, do not modify this.
4.2.3.1 Network Configuration
The network configuration (at offse t 0x100 in the datalogger file) is stored as per the defined
structure.
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struct net_config {
uint32_t key;
uint8_t macaddr[6];
uint8_t dhcp;
ip_addr_t ip;
ip_addr_t gw ;
ip_addr_t mask;
char hostname[64];
};
The structure translates to the binary layout in Figure 4.3. The MAC address is shown in red. The
DHCP enable flag is 01, coloured blue immediately following the MAC address. The hostname is up
to 64 characters long, must include a terminating NULL character and is coloured green. Only
bytes from offset 0x100 to 0x180 are shown.
Because DHCP is being used the IP address information is not filled in. The area coloured purple
would contain the IP address information. The remainder is unused.
12
00
69
00
00
00
FF
FF
39
00
64
00
00
00
FF
FF
38
00
67
00
00
00
FF
FF
46
00
65
00
00
00
FF
FF
02
00
00
00
00
00
FF
FF
F7
00
00
00
00
00
FF
FF
D1
00
00
00
00
00
FF
FF
00
00
00
00
00
00
FF
FF
00
54
00
00
00
FF
FF
FF
00
65
00
00
00
FF
FF
FF
01
6C
00
00
00
FF
FF
FF
00
6E
00
00
00
FF
FF
FF
00
65
00
00
00
FF
FF
FF
00
74
00
00
00
FF
FF
FF
00
42
00
00
00
FF
FF
FF
00
72
00
00
00
FF
FF
FF
Figure 4.3 Network Configuration Layout
4.2.3.2 UART Configuration
The UART structure (at offset 0x200) consists of a 32-bit value for the baud rate, shown in red;
the number of data bits in blue; the parity bits in green; and number of stop bits (0 = 1 stop bit)
in purple.
struct uart_config {
uint32_t key;
int baud;
uint8_t bits;
uint8_t parity;
uint8_t stop;
uint8_t flow ;
};
The flow control, orange, is not implemented. The remainder is unused.
The layout in the datalogger file is shown in Figure 4.4. Only bytes from offset 0x200 to 0x220 are
shown.
13 29 38 49 00 4B 00 00 08 00 00 00 FF FF FF FF
FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
Figure 4.4 UART Configuration Layout
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5 Performance
The following throughput results were obtained. These values are subject to verification and
change.
The measurement was made by timing data transmission (from first packet to last ACK packets)
over the Ethernet. The small data sizes will therefore have a larger overhead as partial packets
and delayed ACK packets will overly affect the data rates.
5.1 19200 baud
Data sample size 1720 bytes.
Telnet to UART -> 1433 bytes per second.
UART to Telnet -> 1433 bytes per second.
This is around 90% of the UART capacity.
5.2 115200 baud
Data sample size 1720 bytes.
Telnet to UART -> 3612 bytes per second.
UART to Telnet -> 3612 bytes per second.
This is around 37.5% of the UART capacity.
Larger data samples achieve higher UART utilisations but this is not recorded.
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6 Contact Information
Head Office – Glasgow, UK
Branch Office – Tigard, Oregon, USA
Future Technology Devices International Limited
Unit 1, 2 Seaward Place, Centurion Business Park
Glasgow G41 1HH
United Kingdom
Tel: +44 (0) 141 429 2777
Fax: +44 (0) 141 429 2758
Future Technology Devices International Limited
(USA)
7130 SW Fir Loop
Tigard, OR 97223-8160
USA
Tel: +1 (503) 547 0988
Fax: +1 (503) 547 0987
E-mail (Sales)
E-mail (Support)
E-mail (General Enquiries)
[email protected]
[email protected]
[email protected]
E-Mail (Sales)
E-Mail (Support)
E-Mail (General Enquiries)
[email protected]
[email protected]
[email protected]
Branch Office – Taipei, Taiwan
Branch Office – Shanghai, China
Future Technology Devices International Limited
(Taiwan)
2F, No. 516, Sec. 1, NeiHu Road
Taipei 114
Taiwan , R.O.C.
Tel: +886 (0) 2 8797 1330
Fax: +886 (0) 2 8751 9737
Future Technology Devices International Limited
(C hina)
Room 1103, No. 666 West Huaihai Road,
Shanghai, 200052
C hina
Tel: +86 21 62351596
Fax: +86 21 62351595
E-mail (Sales)
E-mail (Support)
E-mail (General Enquiries)
E-mail (Sales)
E-mail (Support)
E-mail (General Enquiries)
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Web Site
http://ftdichip.com
Distributor and Sales Representatives
Please visit the Sales Network page of the FTDI Web site for the contact details of our
distributor(s) and sales representative(s) in your country.
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G las gow G 4 1 1 H H , U nited Kingdom. Sc otland Regis tered C ompany N umber: SC 1 3 6 6 4 0
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AN_408 FT90x Telnet to UART Bridge
V ers ion 1 .0
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C learance N o.: FT DI# 5 0 0
Appendix A – References
Document References
FT90x Datasheet: www.ftdichip.com/FT90x
lwIP http://savannah.nongnu.org/projects/lwip/
libtelnet https://github.com/seanmiddleditch/libtelnet
PuTTY http://www.chiark.greenend.org.uk/~sgtatham/putty/
tinyprintf http://www.sparetimelabs.com/tinyprintf/tinyprintf.php
AN_365 FT900 API Programmers Manual
DFU AN_380 FT900 Bootloader DFU Usage
TN_157 Ethernet Explained
AN_408 Firmware: http://www.ftdichip.com/Support/SoftwareExamples/FT90X/AN_408.zip
Acronyms and Abbreviations
Terms
Description
CGI
Common Gateway Interface
DFU
Device Firmware Update
HTTP
HyperText Transfer Protocol
IP
Internet Protocol
MAC
Media Access Controller
SSI
Server Side Include
USB
Universal Serial Bus
UART
Universal Asynchronous Receiver and Transmitter (Serial Port)
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Appendix B – List of Tables & Figures
List of Tables
Table 2.1 Project Files Overview ................................................................................................... 4
List of Figures
Figure 3.1 Main Function Flowchart............................................................................................... 8
Figure 3.2 UART to Telnet Function Flowchart ............................................................................... 9
Figure 3.3 Telnet to UART Function Flowchart ............................................................................. 10
Figure 4.1 Web Configuration Interface....................................................................................... 11
Figure 4.2 PuTTY Telnet Client .................................................................................................... 12
Figure 4.2 Network Configuration Layout .................................................................................... 14
Figure 4.3 UART Configuration Layout ........................................................................................ 14
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Appendix C – Revision History
Document Title:
AN_408 FT90x Telnet to UART Bridge
Document Reference No.:
FT_001319
Clearance No.:
FTDI# 500
Product Page:
http://www.ftdichip.com/FTProducts.htm
Document Feedback:
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Revision
1.0
Changes
Initial Release
Date
2016-04-27
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