Resources for embedded micro-controller firmware development
Your feedback, comments and
enquiries are welcome. *** I do custom electronics design and firmware development *** BERT: "Basic Embedded Real-Time" (operating system) for micro-controllers There's a
lot of embedded RTOS's around and they all have their
pros and cons. The "cons" are mostly related to
licence requirements (i.e. expense) and/or unnecessary
complexity (i.e. unwanted overheads on MCU speed and
memory). An
example firmware application based on BERT is customised
for the Motorola/Freescale 'HC12 processor family (68HC12,
HCS12, etc). BERT is freeware and is distributed as a
suite of C source code modules. ALERT: "A Light Embedded Real-Time OS" for Low-End Micro-controllers ALERT
is a smaller operating system, designed to reduce
processor and memory overheads to a bare minimum. It is
ideally suited to 8051 core micro-controllers
and others having limited on-chip RAM capacity (e.g. AVR,
PIC, 6805, 'HC08). ALERT operating system for AT89C5131 Example firmware based on ALERT is customised for the Atmel AT89C5131 USB micro-controller (8051 core). The code incorporates a "host command interface" (HCI) with resident "debug monitor" and a suite of OS functions to support various MCU resources, including on-chip UART, SPI, EEPROM and USB device controller. The HCI is accessible via the UART or USB port. The USB device "stack" uses the Communications Device Class (CDC), implementing a "virtual UART" function library designed for USB-to-Serial converter applications. Windows (2000/XP) incorporates a USB CDC driver, so the host PC application software can communicate with the device via a "Virtual COM port". HyperTerminal may be used for testing. New
release: ALERT_C5131 version 3.3 Download ALERT C5131 v3.3 (zip file) NB: ALERT source code was originally written to suit the "Hi-Tech C 8051" compiler. The free "demo" version of this compiler could be used to build the ALERT firmware. Unfortunately, Hi-Tech Software no longer provides or supports 8051 compilers -- the company now specializes in PIC micro-controller code development tools. Don't panic! There is another free C compiler available -- SDCC 8051. Google with "SDCC 8051 compiler". Of course, there will be some changes necessary to the source code to make it compile using the SDCC. One day, I will get around to porting ALERT to the SDCC tools. Meanwhile, I would be grateful to hear from anyone who has already done so! Hardware platforms for AT89C5131 development ALERT firmware runs on Atmel's AT89STK-05
Evaluation Board and Futurlec's "USB Development
Board" (www.futurlec.com). Please email me for further details... address is at top of page. AT91SAM7S (ARM) Example Firmware This "SAM7 Debug Monitor" is a complete firmware application comprising target-resident debugging facilities and example peripheral drivers. It runs on Atmel's AT91SAM7S-EK evaluation board and compatible hardware platforms. The firmware provides a basic framework upon which to develop user applications. The firmware is built using the free GCC tools. Release v2.2 with USB CDC function library The USB CDC "Virtual UART" library (developed by MJB) is well structured, richly annotated, and much simpler than Atmel's example "USB framework" code. A Windows host driver file is included. Students of electronics technology and I.T. will find this firmware helpful to implement a USB CDC project. For details, see Guide to MJB's SAM7 Debug Monitor (with GNU/GCC Build Notes) Download AT91SAM7S Debug Monitor v2.2 here (150KB zip file) ATmega128 (AVR) Debug Monitor This AVR Debug Monitor is a complete stand-alone program with a full-featured command-line user interface (CLI), similar to that provided in the 'BERT' operating system. The monitor makes a good starting point for the development of application firmware for the ATmega128 and similar AVR processors. A target-resident debug facility is particularly useful if you don't have access to a JTAG ICE debugging tool. Download ATmega128 Debug Monitor here (20KB zip file) ATmega128 (AVR) Bootloader Design Note The Design Note provides essential information for the development of bootloader code to suit the ATmega128 and similar AVR processors. Included in the resource pack are source files and a customized XLINK linker command file. Download ATmega128 Bootloader Design Pack here (20KB zip file) A very good introduction for novices can be found at... http://www.usbmadesimple.co.uk/ The major difficulty with USB, in my experience, is to produce the host-side (Windows or Linux) driver software. Windows has "built-in" drivers for some USB device "classes", e.g. HID, CDC, MSD (Mass Storage), Audio, Video, etc, but there is no "general purpose" class. And you still have to create a "driver information file" (*.inf), which can be hard to get right! There are two device classes which I have found to be relatively easy to work with for "general-purpose" data transfer applications... USB Communications Device Class (USB-CDC) Using a relatively simple driver information file (*.inf), the communications device class (CDC) allows your device to talk to the host PC via a "virtual COM port". This means that your USB device appears to your PC application software as a serial ("RS232") device, just like a physical COM port, but faster. This is probably the simplest method to implement a full-speed USB connection.* You can use Hyper-Terminal to test your device, if the Bulk-In/Out data is encoded as printable ASCII chars. This is the scheme I chose to use for my AT89C5131 and AT91SAM7S example firmware. *Note: The maximum data transfer rate using USB CDC with a "virtual COM port" is about 1Mbit/sec. (This is a Windows driver limitation, not a USB speed limitation.) USB Test & Measurement Class (USB-TMC) For many applications, the Test & Measurement Class (USBTMC) has distinct advantages over other USB device classes. In fact, its only shortfall is the absence of isochronous transfers which, for the majority of applications, won't be a concern. Although targetted towards instrumentation, as a replacement for the ageing "GPIB" (IEEE488 bus), the USBTMC protocol is very generalized and well suited to a broad range of applications requiring fast Bulk In and Bulk Out data transfer. Perhaps the most compelling reason to use USBTMC is that you don't need to develop host-side driver software or driver information (.inf) scripts. Your host PC application software communicates with USBTMC devices via a third-party 'application program interface' (API). The API provides a library of standardized I/O functions designed to facilitate transfer data to and from compliant USBTMC devices. One such standard is "VISA" (Virtual Instrument Software Architecture). A VISA API library is available from either National Instruments or Agilent Technologies. (These are free downloads -- refer to company websites.) The VISA API incorporates USBTMC host driver software. The driver detects and adapts itself automatically to each unique TMC device connected. Both the NI and Agilent VISA packages come with an interactive test utility which may be used to verify that a TMC device is communicating correctly with the host controller. The VISA API library is provided in the form of a linkable object code file (DLL). These are available for both Windows and Linux. For a Windows host, application software can be developed in Visual Basic or Visual C/C++. National Instruments' LabView software also supports VISA-compliant USBTMC devices. USBTMC/USB488 Reference Design Now available from MJB... a USBTMC device firmware stack meeting the following objectives:
Initial target platform is Atmel AT91SAM7-xxx (ARM7) with on-chip USB peripheral. The example "application layer" and USBTMC "class layers" (source modules) have been designed to be independent of hardware platform, so the code can be more easily ported to other platforms. The source code and supporting documentation is of professional quality. Commercial product developers... If you are interested in
obtaining a USBTMC Reference Design, please contact me
for details. Recommended Windows Utilities for USB Testing & Debugging Microsoft USBView - USB Connection Viewer USBView is
a free utility from Microsoft which displays the USB
connection tree and shows any USB devices connected,
together with their configuration data (descriptors).
This is very useful for diagnosing USB enumeration
problems, with or without the device driver installed on
the host PC. USBView runs under Windows 98, ME,
2000 and XP. USB Monitor from HHD Software Co. USB Monitor
is a Windows application that logs USB data transfers
between the host and selected device(s). This is an
excellent piece of software, well worth the small price
asked (under us$40 for the 'lite' version). There's a
trial version too. Maxim MAX3420E USB Peripheral Controller The MAX3420E is is a very well designed device. It uses a fast SPI connection to the micro-controller instead of a parallel bus. The chip has automatic recovery from bus errors. The register set is devoid of unnecessary complexity, which makes it a breeze to develop driver firmware. The chip is well supported with documentation available from Maxim's website. The datasheet is clear and comprehensive. The FAQ file demystifies and explains aspects of USB which novices often find intimidating. Maxim's sample driver firmware gives you the essential "bare bones" requirements to get the device to enumerate. I have developed a more generalised firmware library which may be more easily customized to a particular application. The library provides essential "Chapter 9" (enumeration and standard device request) support, plus generic functions for endpoint read and write, status checking, etc. Although the library was developed for the USBTMC/USB488 class, it is easily adaptable to other classes using Bulk-In and Bulk-Out for data transfer, for example CDC. (If there is sufficient demand, I will develop a CDC "Virtual UART" library for the MAX3420E. Meanwhile, you could use the CDC library from ALERT c5131 as a framework. -- MJB.) Download MJB's MAX3420E USB device firmware library * Disclaimer * Source code and other "intellectual property" offered as free downloads on this website are original works of M. J. Bauer, except where acknowledged to the contrary. Otherwise, any resemblance to prior art originated or developed by others is purely coincidental, or due to derivation from similar works or well-established art in the public domain. The author does not accept liability for any adverse consequence of the use of "intellectual property" obtained from this site. |
