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Automation with Embedded CANOpen, p. 24 • Single-Key Touch Chips, p. 69
THE
MAGAZINE
FOR
COMPUTER
A P P L I C AT I O N S #239 June 2010
WWVB Receiver DSP OAE Probe Amp & Otoacoustic Experiments The USB Enumeration Process Explained Understanding DC/DC Converters Custom Interpreter Development
$5.95 U.S. ($6.95 Canada)
www.circuitcellar.com
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SSH Encrypted SERIAL TO ETHERNET SOLUTIONS Instantly network-enable any serial device Works out of the box no programming is required
Device P/N: SB70LC-100CR Kit P/N: NNDK-SB70LC-KIT
$47
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Customize to suit any application with low-cost development kit
SB70LC
256-bit encryption protects data from unauthorized monitoring
2-port serial-to-Ethernet server
Features: 10/100 Ethernet TCP/UDP/SSH/SSL modes DHCP/Static IP Support Data rates up to 921.6kbps Web-based configuration
Device P/N: SB700-EX-100CR Kit P/N: NNDK-SB700EX-KIT
SB700EX
2-port serial-to-Ethernet server with RS-232 & RS-485/422 support
$129 Qty. 1000
Need a custom solution? NetBurner Serial to Ethernet Development Kits are available to customize any aspect of operation including web pages, data filtering, or custom network applications. All kits include platform hardware, ANSI C/C++ compiler, TCP/IP stack, web server, email protocols, RTOS, flash file system, Eclipse IDE, debugger, cables and power supply. The NetBurner Security Suite option includes SSH v1 & v2 support.
Device P/N: CB34-EX-100IR Kit P/N: NNDK-CB34EX-KIT
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CB34EX
industrial temperature grade 2-port serial-to-Ethernet server with RS-232 & RS-485/422 support and terminal block connector
Information and Sales |
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T
ASK MANAGER
THE MAGAZINE FOR COMPUTER APPLICATIONS
Embedded Is Everywhere
June 2010 – Issue 239
E
4
ach month Circuit Cellar delivers need-to-know technical information to embedded design engineers, programmers, academics, and intellectuals interested in computer applications. Its mission is to help readers become well-rounded, multidisciplinary technicians who can confidently bring innovative, cutting-edge engineering ideas to bear on any number of relevant tasks, problems, and technologies—particularly at a time when single-skill “specialists” are rapidly losing relevance. Who are these readers? Only engineers and programmers, right? Wrong. Let me explain why. Most people think there are two main courses of study: liberal studies (e.g., literature, history, music, etc.) and professional studies (e.g., engineering, business, etc). A graduate of the former is, at best, characterized as an urbane scholar; at worst, he or she is considered a “Jack of all trades, master of none” (e.g., the English major). On the other hand, the “professional studies” graduate (e.g., the Engineering major) is, at best, thought of as a focused intellectual with money-making potential. At worst, he or she is ridiculed as a myopic drone with few skills or interests outside his or her technical specialty. Well, Circuit Cellar is challenging the conventional notions of what it means to be educated in 2010. Each month, we reach readers with diverse backgrounds in locations all over the world with engaging editorial content: project articles, tutorials, design/programming techniques, and more. And as a result, we can boast a multi-talented readership with backgrounds ranging from chip design to filmmaking to media art to industrial management. What do they all have in common? An interest in the most hightech of technology. We appeal to a wide audience, but we are not a hobby magazine with multiple “intellectual access points”—such as a plugand-play blinking LED project article for the novice followed by an MCU-based radiation detector article for the pro. Our strength is that we publish a consistently high-end periodical for serious readers seeking to become as technically well-rounded as possible. We recognize that readers don’t want to be typecast as either “hardware engineers” or “software designers.” Nor do our readers with backgrounds outside of electronics engineering consider themselves simple hobbyists who couldn’t possibly find a topic like DSP accessible. We provide professional-level content on everything embedded-related—and these days, since embedded technology is everywhere, that means hardware, software, electronics, programming, and beyond. This issue comprises information on a variety of important topics: a customized interpretor and domain-specific languages (p. 16); MCU-based automation and CANOpen software (p. 24); a probe amp and otoacoustic experiments (p. 36); a featureless clock and signal processing (p. 44); inductors and DC/DC converters (p. 54); USB and enumeration (p. 62); capacitive touch sensors (p. 69); and more. Ready to broaden your horizon? Start reading.
[email protected] FOUNDER/EDITORIAL DIRECTOR Steve Ciarcia
PUBLISHER Hugo Vanhaecke
EDITOR-IN-CHIEF C. J. Abate
ASSOCIATE PUBLISHER Shannon Barraclough
WEST COAST EDITOR Tom Cantrell
CUSTOMER SERVICE Debbie Lavoie
CONTRIBUTING EDITORS Jeff Bachiochi Robert Lacoste George Martin Ed Nisley
CONTROLLER Jeff Yanco ART DIRECTOR KC Prescott GRAPHIC DESIGNERS Grace Chen Carey Penney
NEW PRODUCTS EDITOR John Gorsky PROJECT EDITORS Gary Bodley Ken Davidson David Tweed
STAFF ENGINEER John Gorsky
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[email protected] AUTHORS Authors’ e-mail addresses (when available) are included at the end of each article.
CIRCUIT CELLAR®, THE MAGAZINE FOR COMPUTER APPLICATIONS (ISSN 1528-0608) is published monthly by Circuit Cellar Incorporated, 4 Park Street, Vernon, CT 06066. Periodical rates paid at Vernon, CT and additional offices. One-year (12 issues) subscription rate USA and possessions $29.95, Canada/Mexico $34.95, all other countries $49.95. Two-year (24 issues) subscription rate USA and possessions $49.95, Canada/Mexico $59.95, all other countries $85. All subscription orders payable in U.S. funds only via Visa, MasterCard, international postal money order, or check drawn on U.S. bank. Direct subscription orders and subscription-related questions to Circuit Cellar Subscriptions, P.O. Box 5650, Hanover, NH 03755-5650 or call 800.269.6301. Postmaster: Send address changes to Circuit Cellar, Circulation Dept., P.O. Box 5650, Hanover, NH 03755-5650. Circuit Cellar® makes no warranties and assumes no responsibility or liability of any kind for errors in these programs or schematics or for the consequences of any such errors. Furthermore, because of possible variation in the quality and condition of materials and workmanship of reader-assembled projects, Circuit Cellar® disclaims any responsibility for the safe and proper function of reader-assembled projects based upon or from plans, descriptions, or information published by Circuit Cellar®. The information provided by Circuit Cellar® is for educational purposes. Circuit Cellar® makes no claims or warrants that readers have a right to build things based upon these ideas under patent or other relevant intellectual property law in their jurisdiction, or that readers have a right to construct or operate any of the devices described herein under the relevant patent or other intellectual property law of the reader’s jurisdiction. The reader assumes any risk of infringement liability for constructing or operating such devices. Entire contents copyright © 2010 by Circuit Cellar, Incorporated. All rights reserved. Circuit Cellar is a registered trademark of Circuit Cellar, Inc. Reproduction of this publication in whole or in part without written consent from Circuit Cellar Inc. is prohibited.
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5_Layout 1 5/12/2010 8:27 AM Page 1
What is the missing component? Electronics instructor Ollie Circuits planned to show his class of freshman electrical engineering students how to use a super capacitor as a memory back-up capacitor, but first he wanted to show how the students could make their own super capacitor and demonstrate its charge/discharge cycles with the simple circuit above. Most of the components were already on his workbench, the homemade super capacitor would be made from several layers of lemon juice-soaked paper towels interleaved between several layers of a mystery material to form a multi-layer stack.The stacked layers would then be sandwiched between the two copper-clad PC boards and held together with a rubber band. Ollie rushed to a nearby pet shop. What did he buy? Go to www.Jameco.com/teaser7 to see if you are correct and while you are there, sign-up for our free full-color catalog.
1-800-831-4242 | www.Jameco.com
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239
INSIDE ISSUE June 2010
16 24 36
•
Communications
Custom Interpreter Development An Innovative LED Movie Project Chris Cantrell INTELLIGENT ENERGY SOLUTIONS Home Automation for an Energy-Efficient House (Part 2) Embedded CANOpen Node Hardware & Software Stefan Siegel OAE Probe Amp and Intercom (Part 2) Otoacoustic Experiments Chris Paiano
p. 16, Interpreter Development
p. 36, Otoacoustic Experiments
p. 69, Touch Tech
p. 24, Push Button Switch Modules
44
ABOVE THE GROUND PLANE Totally Featureless Clock (Part 3) Signal Processing Ed Nisley
54
THE DARKER SIDE DC/DC Converter Basics Robert Lacoste
June 2010 – Issue 239
62
6
69
FROM THE BENCH Application Communication with USB (Part 1) The Enumeration Process Explained Jeff Bachiochi SILICON UPDATE Pitch the Switch Tom Cantrell
TASK MANAGER Embedded Is Everywhere C. J. Abate
4
NEW PRODUCT NEWS edited by John Gorsky
8
TEST YOUR EQ SOLUTIONS
15
CROSSWORD
74
INDEX OF ADVERTISERS July Preview
79
PRIORITY INTERRUPT Is It Cheating or Is It Collaboration? Steve Ciarcia
80
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COMPACT USB-TO-I2C HOST ADAPTER The i2cStick brings high-performance I2C to on-the-go mobile developers, test engineers, and field support personnel. The i2cStick is a pocket-size, bus-powered, USB-to-I2C Bus adapter. Simply plug the i2cStick into a laptop’s USB port, connect to a target device with the provided clip-lead or header cable, and start communicating. The i2cStick supports 7-bit slave addressing, bus master or slave operation at standard (100 kHz) or fast (400 kHz) clock rates, and multi-master and arbitration detection capability. The device is 3.3- to 5-V compatible, provides switch-enabled bus pull-ups, has a 5-V power source for external devices, and includes over-voltage, reverse-voltage, ESD, and dual-stage fuses for laptop or desktop computer protection. Free utility software includes the iBurner I2C Bus EEPROM programming software, and Message Center messaging software. Application developer support includes a .NET Class Library, LabVIEW Virtual Instrument Library, ASCII-Text application program interface (API), Virtual Communications Port (VCP) interface, and sample software projects in VB, C, C++, and MFC. VCP drivers are available for Windows, Linux, and Mac. i2cStick’s API compatibility extends to other MCC I2C Bus adapters, including the iPort/USB, iPort/AFM, and iPort/AI. Prices range from $150 to $250 depending on interface cable configuration and order quantity.
Micro Computer Control Corp. www.mcc-us.com
GSM/GPRS, CDMA AND UMTS MODEMS
SMALL-SIZED POWER AMPLIFIER REDUCES COMPONENT COST
The highly successful Terminus platform of GSM/GPRS, CDMA, and UMTS modem devices is expanding to include a new range of board-level, plug-in modules for use in wireless communication applications. Developed in cooperation with wireless module manufacturer Telit Wireless Solutions, these interchangeable modules are specifically designed for quick and easy integration into all new and existing M2M designs. Combining full M2M functionality with the flexibility of a standard “plug-in” DIP design, the Terminus GSM865CF, Terminus CDMA864CF, and Terminus UMTS864CF share the same mechanical footprint and offer users the ability to easily configure their applications for communication via any cellular protocol. All plug-in modules operate at 5 V and the GSM and UMTS modules include SIM Card sockets. To allow for easy integration, these cellular devices are available as open frame modules. Enclosed designs employing the modules will be available as requested by customers. Pricing is $85 per unit in 1,000-piece quantities.
California Eastern Laboratories (CEL) is now shipping its new uPG2251T6M GaAs power amplifier (PA). The new PA eliminates the need for RF component matching, which reduces component count, saves bill of materials cost, and simplifies procurement. The new 2251 PA is ideal for applications such as Bluetooth modules designed into notebooks, mobile phones, and headsets. It’s also ideal for 802.15.4/ZigBee modules, which have wide applicability in automatic meter reading, wireless security, cable replacement, and intelligent lighting control systems. The PA boosts range for CEL’s extensive line of 802.15.4/ZigBee devices. At 2 mm × 2 mm, the new 2251 is one of the smallest power amplifiers in the industry, enabling product designs where PCB space is scarce such as smart phones, digital cameras, hand-held gaming devices, and other consumer electronics. The amplifier operates off a supply voltage of 3 V with a 0- to 1.8-V control voltage. Pricing is $0.82 in quantities of 100,000 and evaluation boards are available.
June 2010 – Issue 239
Janus Remote Communications www.janus-rc.com
8
California Eastern Laboratories www.cel.com
S W E N CT DU R O P NEW Edited by
CIRCUIT CELLAR®
•
John Gorsky
www.circuitcellar.com
9_Layout 1 5/12/2010 8:28 AM Page 1
®
Stellaris
Connected. Versatile. Cost-effective.
Stellaris LM3S9B90 Ethernet Evaluation Kit
Stellaris LM3S8962 Evaluation Kit
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Stellaris LM3S6965 Ethernet Evaluation Kit
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WORLD’S SMALLEST RFID READER-WRITER MODULE The LXRW series is the world’s smallest UHF RFID reader-writer module. The combination of its small size, functionality and fast integration make the cost-effective LXRW ideally suited for stationary and handheld UHF generation 2 RFID reader-writer units, including cell phones and other devices that require embedded RFID capabilities. Measuring only 23 mm × 13 mm × 2.8 mm, the surface-mount module is 85% smaller in footprint and 92% smaller by volume when compared to existing reader-writer modules with the same output power. Despite its dramatically reduced size, the LXRW is feature rich, offering complete RF and baseband functionality. Included in the module are the processing unit, antenna-matching circuit, power amplifier, random access memory, generation 2 firmware, and oscillator. In addition, it has three serial port options and a 100-mW maximum output power for ranges up to two feet with a small size antenna. Also, as a surface mount device, the LXRW series can be directly mounted onto a printed circuit board using a standard surface-mount assembly line. Other reader-writer modules typically have a connector which requires a manual connection to a motherboard within the reader production line. Murata’s new module eliminates this costly and time-consuming process. The LXRW reader-writer series sample is available for $120 with significantly lower prices available with volume orders.
Murata Electronics North America www.murata.com
June 2010 – Issue 239
NPN
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CIRCUIT CELLAR®
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2.4-GHz WIRELESS RADIO MODULE PRODUCT FAMILY Laird Technologies announces the introduction of its enhanced LT2510 proprietary 2.4-GHz wireless module product family. The product series includes model numbers PRM110, PRM111, PRM112, PRM113, PRM120, PRM121, PRM122, and PRM123. With a throughput of up to 250 Kbps in half-duplex mode, the LT2510 delivers speedy data rates. In addition, variable output power options of up to 21 dBm (depending on region) enable communication over distances that aren’t achievable with competing technologies. At the same time, a range of ultra-low power modes plus low Tx/Rx power consumption makes the LT2510 ideal for power-restricted or battery-operated applications. Embedded with a robust server-client protocol, the LT2510 permits an unlimited number of clients to synchronize to a single server for low latency communications. The server and all clients in a network can communicate with any radio in range via either addressed or broadcast packets. The configuration and test software allows OEMs to design and test networks to suit their applications. Enhanced API commands provide dynamic packet routing control and network intelligence. With its field-proven frequency-hopping spread spectrum (FHSS) air interface protocol, the LT2510 rejects RF noise, excels in multipath scenarios, allows for co-located systems, and provides an extremely reliable communication link. Numerous “software hooks” provide control and flexibility, allowing designers to mold the communication link around applications, as opposed to squeezing the application into a fixed communication technology or standard. Each transceiver is designed to provide OEMs with a feature-rich, high-performance, configurable, secure, compatible, integrated solution, allowing OEMs to build the most optimized network possible. Contact Laird Technologies for pricing.
Laird Technologies, Inc. www.lairdtech.com
NPN
microOBD 200
www.microOBD.com
OBD-II interpreter module in a DIP-24 package. UART interface, bootloader, 100% compatible with the ELM327 command set.
$49
OBDLink
www.OBDLink.com
$99
#1 PC based OBD-II scan tool. USB, RS232, Bluetooth, and WiFi options. Free OBDwizTM software included.
ECUsim 5100
www.ECUsim.com
Professional multiprotocol OBD-II ECU simulator. Functional and physical addressing, three virtual ECUs, software configurable.
Full support of all OBD-II protocols Free regular firmware updates Discount code for free shipping: CC1006FS
Questions? Email
[email protected] www.circuitcellar.com
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CIRCUIT CELLAR®
June 2010 – Issue 239
$549
13
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EDGE RATE CABLES FOR HIGH-SPEED, RUGGED, & TEST APPLICATIONS Samtec’s High-Speed Edge Rate Twinax, Micro Coax, and Direct-to-Lead Coax Cable Assemblies incorporate its rugged 0.8-mm (0.0315″) pitch Edge Rate terminals and sockets (ERM8/ERF8 Series), which are designed for superior signal integrity and impedance control and reduced broadside coupling. The result is a robust family of cable-to-board interconnect solutions ideal for high-speed and long cable run applications as well as for emulation testing (the ERF8 Series connector has been specified as the standard board level interface by NEXUS, POWER.org, and ARM). All three systems feature rugged friction latches that increase de-mating to 7 lb. Edge Rate 34 AWG, 50-Ω coax cable assemblies include the Micro Coax Cable (ERCD Series) and the Direct-to-Lead Coax Cable (ERCDA Series) which is rated from 890 MHz (1 m) to 7.90 GHz (6″) and is hot pluggable. The Direct-to-Lead cable is also designed to optimize signal integrity with a patent-pending direct termination that eliminates the need for a PCB. The Edge Rate 30 AWG, 100-Ω Differential Pair Twinax Cable (ERDP Series) is rated from 1.41 GHz (1 m) to 6.33 GHz (6″) and is also hot pluggable. The Micro Coax and Twinax assemblies also have an optional squeeze latch system that prevents unintentional de-mating. Pricing depends on the connectors and configuration required.
Samtec, Inc. www.samtec.com
NPN N
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Education Never Ends. Everything you need to know to get started.
By: Michael Parker ISBN: 9781856179218 $54.95
By: Gina Smith ISBN: 9781856177061 $44.95
By: William Kafig ISBN: 9781856177047 $44.95
By: Robert Lacoste ISBN: 9781856177627 $44.95
June 2010 – Issue 239
Stop by booth 1823 at ESC West to check out these titles and more!
14
Save 20% when you buy at the show. Register for our e-news at newnespress.com www.newnespres s.com
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20100490_AD_CircuitCellar_034_1200.indd 1
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CIRCUIT CELLAR
Test Your ANSWERS for Issue 238
EQ
Edited by David Tweed
Answer 1—The Fourier transform is a mathematical relationship between a continuous time-domain function and the equivalent frequency-domain function. As such, there are specific solutions for specific functions, but not for arbitrary ones. The discrete Fourier transform (DFT) is the same relationship between a set of values representing a time series and the equivalent set of values that represent a frequency series. Since it is computed numerically, it can handle arbitrary values in either series. The fast Fourier transform (FFT) is a particular implementation of the DFT that takes advantage of certain redundancies in the numerical operations that are performed. This reduces the number of basic operations—such as addition and multiplication—that need to be performed. In “big O” notation, the DFT is O(N2), while the FFT is O(N log N). However, the FFT computes all of the frequency bins, whether you need them or not. If you’re only interested in a few of the bins, it often requires fewer CPU cycles to compute them directly with the DFT algorithm than to execute the full FFT algorithm. Answer 2—A Fourier transform gives you information about the component sine waves that are part of a complex signal, including their frequencies, amplitudes and phase relationships. In a tone detection application, you’re really just looking to see whether a particular frequency component is present at a level above a certain amplitude threshold. As such, you don’t really care about phase information at all. In terms of the implementation of a DFT, this means that the sine and cosine functions that you generate to multiply with the incoming signal don’t need to
What’s your EQ?—The answers are posted at
www.circuitcellar.com/eq/
have any particular phase relationship, and you can in fact use a fixed set of coefficients for each calculation that include the “window” function (lowpass filter) implicitly, rather than calculating it as a separate step. Answer 3—While the DFT can be computed on a time series of any length, the FFT is usually implemented on blocks of samples that are a power of two in length. As a result, it is necessary to decide what block length is best for a particular application. The trade-off is frequency resolution vs. time resolution. Frequency resolution is the ability to distinguish two different frequencies that are close together. Time resolution is the ability to determine when a tone starts or stops. A small block size has good time resolution, but poor frequency resolution, while a large block size has the opposite characteristics. Answer 4—The Goertzel algorithm is a one-bin nonrecursive DFT calculation converted into an equivalent recursive form (requiring much less data storage and very few CPU cycles per sample) that comes up with the same answer. In tone detection applications, it is often useful to implement the detection algorithm over a “sliding window” of input samples, rather than breaking the input samples into blocks at arbitrary boundaries. This gives you a little more leeway with respect to the frequency- vs. time-resolution trade-off. While it would be prohibitive in terms of CPU cycles to compute an FFT over a sliding window (a complete FFT for each input sample), and almost as bad to do a complete Goertzel algorithm for each sample, the DFT lends itself quite nicely to a sliding-window implementation. Contributed by David Tweed
You may contact the quizmasters at
[email protected] Are all oscilloscopes created equal? "Cleverscope is still the best out there, keep up the good work !!!!!" Karl, USA Ours: Ours
100 MHz MSO 8M Samples 14 bit
We have proper DC offset and 10, 12 or 14 bit resolution so you see the detail in the signal. In this example we digitize over the range 1.2 to 1.5V. With the 10 bit ADC the resolution is 0.3/1000 = 300 uV (even better at 18uV with the 14 bit ADC). You see all the detail. The spectral response has good SNR.
Theirs : Communications systems transfer voice, data and video. These signals are often digitized. To make best use of scarce bandwidth, you need good signal to noise (SNR), good bandwidth occupancy, low spectral leakage, and low distortion. The Cleverscope 14 bit scopes provide all the tools needed to verify the performance of your design.
You don’t see all the detail, and the spectral response has poor SNR.
Signal: Video color burst, as presented to an ADC. Task: check DC levels, noise, and spectral leakage.
www.cleverscope.com www.circuitcellar.com
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CIRCUIT CELLAR®
In the USA call:
June 2010 – Issue 239
+ Two mixed signal triggers + Protocol decoding + Spectrum analysis + Symbolic maths + Custom units + Copy & paste + Signal generator + USB or Ethernet + 4 or 8M samples storage + 100 MHz sampling + Dual 10, 12 or 14 bit ADC + Ext Trigger, 8 Digital Inputs + 1 MSa/sec charting
They don’t have DC offset, and only 8 bits. They have to digitize over -2V to +2V to capture this signal. The resolution is 4000/256 = 16 mV, 52x worse than ours.
Communications
15
F EATURE
2105018_Cantrell_Chris Post FE for PP_Layout 1 5/12/2010 9:46 AM Page 16
ARTICLE
by Chris Cantrell (USA)
Custom Interpreter Development An Innovative LED Movie Project Ready to make movies? Here you learn how to create two specific CPUs, each with its own unique language: one for movie frames and one for music. The design reads movie frames from an SD card and displays them on a 48 × 32 LED display while generating music with six independent voices.
I
can see the day coming when my nerdy grandchildren will ask me what embedded design life was like when I was young. I will tell them about the days when opcodes were rigid things given to us by CPU makers, and we coded with general-purpose programming languages we slung like clumsy hammers when a more sophisticated, elegant dialect was needed. Every project has its own specific hardware requirements, yet today we end up forcing a general off-the-shelf embedded controller to fit different needs. The Parallax Propeller chip is a step forward from this brute-force general solution. Instead of providing a fixed set of hardware functions, the chip offers eight pieces of putty you can
June 2010 – Issue 239
a)
16
mold into the specific hardware functions you need. These “putty” cogs also serve as the basic building blocks for custom CPUs tailor-fit to your specific project needs. And along with these homegrown CPU opcodes, you can create “domain-specific languages”—programming languages custom-built for a specific application. In this article I’ll explain my “putty” approach to designing with the Propeller chip. I will show you how I used the cogs to create several virtual hardware modules mapped into the Propeller chip’s shared memory space. I’ll also show you how I used the cogs to create two specific CPUs, each with its own unique language: one for movie frames and one for music. Finally, I’ll describe my SPIN and Java b)
Photo 1a—The running movie ornament shows the combined creativity of my entire family. Here a rather plump partridge sits on a limb in a pear tree. b—The project opens to reveal the components inside. The right (top) half includes the four LED boards glued together with the speakers, an amplifier, and the SD card. The left (bottom) half includes the Propeller circuit and sound chips wired on a solderless breadboard. A single 5-V regulated wall wart powers the project. CIRCUIT CELLAR®
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2105018_Cantrell_Chris Post FE for PP_Layout 1 5/12/2010 9:46 AM Page 17
toolchain to get you started with your own custom CPUs and the language compilers to support them. I’ll demonstrate my virtual hardware, custom CPUs, and domain-specific languages with my Propeller LED movie project (see Photo 1a). The project reads movie frames from an SD card and displays them on a 48 × 32 LED display while generating music with six independent voices. The whole family chipped in and made the movie sequences for each of “The 12 Days of Christmas.” The project makes a nice seasonal ornament that I add to each year.
HARDWARE The Propeller chip is a collection of eight lightning-fast RISC processors. Each processor has its own tiny 2 KB of RAM for data and code. All eight processors share a large pool of 32 KB used for data (code cannot execute directly from this shared space). There are no interrupt lines and no integrated peripherals. Instead, you must write the peripheral functions in software and dedicate one of the eight processors to bit-banging the I/O pins. Software functions are slower than an integrated peripheral, but the software approach allows you to create a wide www.circuitcellar.com
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CIRCUIT CELLAR®
variety of peripherals for different projects. I like to think of the Propeller cog CPUs as eight pieces of putty between the I/O pins and the 32 KB of shared RAM space. To the outside world, the putty looks like standard hardware devices driving the I/O pins. Virtual hardware modules twiddle the I/O signals just like the real things. On the inside, the putty looks like standard memory-mapped hardware tied into the shared 32-KB RAM space. The application sees the virtual hardware as a set of hardware registers that work very much like “the real things.” I started this project by designing the virtual hardware modules. I implemented each peripheral in cog RISC assembly, and I tested each module with a small SPIN program that writes and reads the memory mapped virtual registers. Figure 1 shows the project’s circuitry. Photo 1b shows the project built on a solderless breadboard The display for this project is a combination of four DE-DP016 boards from Sure Electronics. Each board has a 24 × 16 LED matrix and an interface/driver chip that accepts serial SPI-like commands from a host controller. I glued four boards together in a 2 × 2 block to make a single display
of 48 × 32 LEDs. The display boards require a single 5-V supply, and I used a 5-V regulated wall wart to power the entire project. I used a 3.3-V power regulator to step down the 5 V for the Propeller chip. I discovered the hard way that the display boards do not recognize the 3.3 V high I/O signals from the Propeller. I used 7404 TTL inverter gates to bump each board’s CHIPSELECT/DATA/WRITE signals up to 5 V. TTL chips, of course, recognize 3.3 V as high. I used one Propeller cog as putty to map the display hardware into the propeller shared memory as two registers: Address and Command. An application writes the address of the pixel data to the hardware Address register and then writes a nonzero value to the Command register. The hardware cog then pulls the data from shared memory and clocks it out to the displays in the background. When the display has been drawn, the hardware cog sets the Command register back to zero. I used two Texas Instruments AY38910 sound chips for the audio in the project. These chips were popular in computers and arcade games in the 1980s. If you have ever walked past an arcade, you have heard their voices from games like Frogger, Tron, Moonpatrol, Timepilot,
June 2010 – Issue 239
Figure 1—Take a look at the power, EEPROM, and Propeller circuit. (More info is available on Parallax’s website.) The SD card and sound chips hook to the Propeller’s I/O pins with two resistors. Two inverter chips boost the Propeller’s 3.3-V I/O pins to 5 V for the display.
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2105018_Cantrell_Chris Post FE for PP_Layout 1 5/12/2010 9:46 AM Page 20
hardware with missing feaSpy Hunter, and many oth32-KB Shared tures like a frequencyers. Each chip generates RAM sweep function or separate three separate voices. Each volume envelopes for all voice can be a tone or noise. voices. The application sees The host controller can Sound hardware these additional services as directly control the frequenmore memory-mapped cy/volume of a voice over locations. It doesn’t know time or configure an onLED hardware (or care) which functions board envelope generator to are in the hardware and modulate a voice’s volume 2-KB Frame which are synthesized in automatically. cache SD hardware software. The details are The AY38910 chip inter2-KB Frame cache hidden under the putty. faces to the host controller The SD card interface in with a single 8-bit bus and this project is the same two control lines. Each chip Music CPU Movie CPU hardware and driver code I has a bank of 16 8-bit regisMusic used in two other projects. ters you twiddle to control program (Refer to my articles in Cirthe three voices and envecuit Cellar 205 and 209.) In lope generator. The host Movie program this project, I used a cardcontroller first latches in the socket break-out board target register’s address on from SparkFun Electronics. the bus and then writes (or Figure 2—The Propeller’s 32-KB RAM acts like a traditional The four SPI signals tie reads) the register’s value address/data bus. Four Propeller COGs at the top of the figure map directly to the Propeller’s using the same bus. hardware devices to virtual hardware registers within shared RAM. I/O lines with a couple of I took apart a cheap miniTwo virtual CPUs at the bottom read their programs from the shared resistors. speaker system and glued RAM and manipulate the virtual hardware registers. A single register The SD driver putty is the circuit board and speakshared between CPUs syncs the movie frames to the music beats. based on Tomas Rokicki’s ers to the back of the LED work available for download through putty cog to map the sound chips to display board for a single audio/visual the Parallax Propeller Object the propeller shared memory bus. The module. I twisted all six audio output Exchange. I modified it to follow the application sees four registers: Chip lines from the sound chips together FAT tables to the first file on the disk, Number, Address, Value, and Comand hooked them directly to the input and you must reformat the card every mand. The command value is 2 for of the mini-speaker system. A little time you write a new data file for your “read” or 1 for “write” to the target RC networking would improve the project to read. This is a minor inconregister on the target chip. The driver sound quality, but the “ice-cream venience that allows the SD driver code code that talks to the sound chips is truck” sound goes nicely with the to fit nicely in a single cog. quick and short, leaving plenty of low-resolution LED display. The application sees the SD hardware time and space to extend the sound I used another virtual hardware
June 2010 – Issue 239
Listing 1—These comments in the SPIN file configure the engine and its compiler automatically. A Java program reads through the configuration and comments or uncomments sections of the remaining CORE code as required. The compiler then reads the configuration to know which CORE commands to generate for the target engine.
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' CALL-STACK SIZE ' #define CALL_STACK_SIZE = 5 // Number of longs reserved for the call stack ' ' MULTIPLY AND DIVIDE ' #define MULTIPLY = NO // Include the generic multiply routine (auto if MULT=YES) ' #define DIVIDE = NO // Include the generic divide routine (auto if DIV or REM = YES) ' ' CORE COMMANDS ' #command coreGOTO = YES ' #command coreGOTOCOND = YES ' #command coreCALL = YES ' #command coreRETURN = YES ' #command coreSTOP = NO ' #command corePAUSE = YES ' #command coreSYNC = YES ' #command coreNATIVEMATH = YES ' #command coreMULT = NO ' #command coreDIV = NO ' #command coreREM = NO
CIRCUIT CELLAR®
•
www.circuitcellar.com
2105018_Cantrell_Chris Post FE for PP_Layout 1 5/12/2010 9:47 AM Page 21
Vinculum VNC2 ASM Source
2 Core compiler
1 Dialect compiler Core Spin 3 Dialect Spin Byte code
Figure 3—Generating executable domain-specific language code is a three-part process. First, you add your dialect-specific commands to the core SPIN code. You configure the core engine features in the code comments. The Java preprocessor tool (1) generates the CPU code in SPIN for the Propeller. Next, you add your dialect-specific compiler code to the Java core compiler. Then your own assembly language compiles (2) into byte code for your custom CPU. Finally, the SPIN engine interprets your compiled program (3).
CUSTOM CPUs Hardware is only part of the project. Without application code to pull the strings, the hardware is a mindless lump of lifeless limbs. The RISC cogs are great for small, fast, bit-banging hardware drivers, but they aren’t very good at running applications. Application code tends to be much longer than driver code. The Propeller cog address space is 2 KB, but the memory is organized into 4-byte words. A cog has only 512 addressable locations for code and data. That’s not much space when you are trying to code up the many pathways of an application to play chess. Application code tends to use data in more complicated ways. Applications need pointers and diverse addressing modes. The Propeller RISC opcodes, however, have no indirection at all. Pointers are simulated by writing addresses into later instructions, and there is no stack to support a highlevel application language. What I would really like to do is pop the top off the Propeller chip and replace one or two of those fast RISC www.circuitcellar.com
•
Spin preprocessor
CIRCUIT CELLAR®
cogs with a slower CPU that has the space and power I need to write applications. The putty approach allows me to do just that. A CPU is, after all, just a piece of hardware in the memory space of the system. By modeling the CPU features I want in the cog putty, I can create a processor with the complex addressing modes I want. And my application code runs (virtually) out of the much larger byteaddressable, 32-KB RAM. Note that a virtual machine for the Propeller is not a new idea. Parallax designed its SPIN language interpreter to solve these very application limitations. The SPIN interpreter is programmed into the Propeller’s ROM, and the Propeller IDE is a rich graphical editor/compiler for the SPIN language. So why reinvent the wheel with a new virtual machine? The SPIN interpreter is a general-purpose engine—a wheel designed to work reasonably well for a large set of axles— yet it does not fit any one axle perfectly. For example, the command set includes a square-root function. I don’t need square roots in my LED graphics language, but I do need a Bresenham
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USB MADE EASY www.ftdichip.com June 2010 – Issue 239
as three registers in shared propeller memory: Sector Number, Destination Address, and Command (read or write). The application writes the file sector number and the destination memory address. Then it sends a “read” to the virtual hardware “command” register. When the command location goes to zero, the data has been read from card to memory. Figure 2 shows the various putty cogs mapped into the 32-KB shared RAM space. No actual memory addresses are shown. The figure simply shows the individual data areas and how they are shared. The two custom CPUs (discussed below) write to all the hardware registers. They communicate with each other through a single virtual register as shown.
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2105018_Cantrell_Chris Post FE for PP_Layout 1 5/12/2010 9:47 AM Page 22
Listing 2—It may look like a strange new language syntax, but it is really assembly language—one instruction per line. The for construct and the $ memory references are preprocessed by the BLEND tool available for all assembly languages. The added movie-specific commands are shown in all caps. Notice how RENDERFRAME is called first with a constant and later with a memory reference. Parameters are resolved automatically by the CORE engine.
June 2010 – Issue 239
// $nextCluster = next cluster to load // $numFrames = number of frames in current cluster ShowCluster: call FlipPages // Swap cache and active pages WAITONTICK // Wait for the music trigger RENDERFRAME $renderPage, 0 // Draw first frame on new page LOADCLUSTER $cachePage, $nextCluster // Start loading the next sector for($x=1;xP[OHOVZ[VMTVK\SLZZ[HUKHSVUL Gateways
HKHW[LYZ07LUHISLKNH[L^H`ZHUKP+PNPKH[HZLY]PJLZ+PNPOHZ[OL[VVSZ[VZLL`V\YWYVQLJ[ [OYV\NOMYVTILNPUUPUN[VLUK
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