Does anyone know of a good learning resource for building your own bootloader for an embedded system? From reading various textbooks, I have a good overview of what a bootloader is supposed to do, and some textbooks include snippets of assembler to show how the bootloader should be built.
However, when I search for resources/tutorials that describe how to build a bootloader, everything I've found so far is either too advanced, (assuming a knowledge of certain preliminaries and are thus hard to follow), or, they are dealing with creating a bootloader for a pc or an emulator. Ideally I'm looking for a single resource/book, that covers preliminaries, and walks me through the process. I'm happy to purchase a particular chip, and relevant cables, if the tutorial/textbook requires that.
The term bootloader is quite broad, so does your quest have roots in a few dozen lines of code with a serial bootloader or are you interested in a linux type full blown operating system (uboot) that has gobs of features and drivers and stacks?
If you dont already know that answer or dont know what I am talking about you need to figure that out, I would start small...even if you desire the huge monster operating system solution, you should start with bare metal (which is what a bootloader is, a bare metal program) chip comes out of reset, your code runs first, blinks an led. Then control the rate of the blinking led, then if you have a push button read the push button and make it change the led (demonstrating input and output). Then find and use a timer to blink the led if you didnt already (use polling first please, interrupts later). Now you can do clock math and have an idea how the chips clock tree is so use that to get a uart up, tx only first, then rx/tx echo what your receive. THEN you are ready to talk about your first bootloader, which should involve some serial protocol (invent your own or use xmodem or something) that actually "boots" and then lets you "load" other programs after booting.
You can do all of this (well virtual leds in some other form) using simulators, and that may not be a bad idea since the hard part of bare metal is first off controlling the assembler compiler and linker to make a binary that actually boots up and runs. Then piles of sub $10 and sub $20 boards that you can learn to write a bootloader for (msp430 launchpads, the other launchpads, stm32f0 and f4 discovery boards, the raspberry pi, probably not the beagles avoid those for now, oh and a myriad of avr based boards, avoid x86 start with microcontrollers, arm, avr, msp430).
Related
I have a doubt regarding the reset due to power up:
As I know that microcontroller is hardwired to start with some particular memory location say 0000H on power up. At 0000h, whether interrupt service routine is written for reset(initialization of stack pointer and program counter etc) or the reset address is there at 0000h(say 7000) so that micro controller jumps at 7000 address and there initialization of stack and PC is written.
Who writes this reset service routine? Is it the manufacturer of microcontroller chip(Intel or microchip etc) or any programmer can change this reset service routine(For example, programmer changed the PC to 4000h from 7000h on power up reset resulting into the first instruction to be fetched from 4000 instead of 7000).
How the stack pointer and program counter are initialized to the respective initial addresses as on power up microcontroller is not in the state to put the address into stack pointer and program counter registers(there is no initialization done till reset service routine).
What should be the steps in the reset service routine considering all possibilities?
With reference to your numbering:
The hardware reset process is processor dependent and will be fully described in the data sheet or reference manual for the part, but your description is generally the case - different architectures may have subtle variations.
While some microcontrollers include a ROM based boot-loader that may contain start-up code, typically such bootloaders are only used to load code over a communications port, either to program flash memory directly or to load and execute a secondary bootloader to RAM that then programs flash memory. As far as C runtime start-up goes, this is either provided with the compiler/toolchain, or you write it yourself in assembler. Normally even when start-up code is provided by the compiler vendor, it is supplied as source to be assembled and linked with your application. The compiler vendor cannot always know things like memory map, SDRAM mapping and timing, or processor clock speed or what oscillator crystal is used in your hardware, so the start-up code will generally need customisation or extension through initialisation stubs that you must implement for your hardware.
On ARM Cortex-M devices in fact the initial PC and stack-pointer are in fact loaded by hardware, they are stored at the reset address and loaded on power-up. However in the general case you are right, the reset address either contains the start-up code or a vector to the start-up code, on pre-Cortex ARM architectures, the reset address actually contains a jump instruction rather than a true vector address. Either way, the start-up code for a C/C++ runtime must at least initialise the stack pointer, initialise static data, perform any necessary C library initialisation and jump to main(). In the case of C++ it must also execute the constructors of any global static objects before calling main().
The processor cores normally have as you say a starting address of some sort of table either a list of addresses or like ARM a place where instructions are executed. Wrapped around that core but within the chip can vary. Cores that are not specific to the chip vendor like 8051, mips, arm, xscale, etc are going to have a much wider range of different answers. Some microcontroller vendors for example will look at strap pins and if the strap is wired a certain way when reset is released then it executes from a special boot flash inside the chip, a bootloader that you can for example use to program the user boot flash with. If the strap is not tied that certain way then sometimes it boots your user code. One vendor I know of still has it boot their bootloader flash, if the vector table has a valid checksum then they jump to the reset vector in your vector table otherwise they sit in their bootloader mode waiting for you to talk to them.
When you get into the bigger processors, non-microcontrollers, where software lives outside the processor either on a boot flash (separate chip from the processor) or some ram that is managed somehow before reset, etc. Those usually follow the rule for the core, start at address 0xFFFFFFF0 or start at address 0x00000000, if there is garbage there, oh well fire off the undefined instruction vector, if that is garbage just hang there or sit in an infinite loop calling the undefined instruction vector. this works well for an ARM for example you can build a board with a boot flash that is erased from the factory (all 0xFFs) then you can use jtag to stop the arm and program the flash the first time and you dont have to unsolder or socket or pre-program anything. So long as your bootloader doesnt hang the arm you can have an unbrickable design. (actually you can often hold the arm in reset and still get at it with the jtag debugger and not worry about bad code messing with jtag pins or hanging the arm core).
The short answer: How many different processor chip vendors have there been? There are many different solutions, as many as you can think of and more have been deployed. Placing a reset handler address in a known place in memory is the most common though.
EDIT:
Questions 2 and 3. if you are buying a chip, some of the microcontrollers have this protected bootloader, but even with that normally you write the boot code that will be used by the product. And part of that boot code is to initialize the stack pointers and prepare memory and bring up parts of the chip and all those good things. Sometimes chip vendors will provide examples. if you are buying a board level product, then often you will find a board support package (BSP) which has working example code to bring up the board and perhaps do a few things. Say the beagleboard for example or the open-rd or embeddedarm.com come with a bootloader (u-boot or other) and some already have linux pre-installed. boards like that the user usually just writes some linux apps/drivers and adds them to the bsp, but you are not limited to that, you are often welcome to completely re-write and replace the bootloader. And whoever writes the bootloader has to setup the stacks and bring up the hardware, etc.
systems like the gameboy advance or nds or the like, the vendor has some startup code that calls your startup code. so they may have the stack and such setup for them but they are handing off to you, so much of the system may be up, you just get to decide how to slice up the memorires, where you want your stack, data, program, etc.
some vendors want to keep this stuff controlled or a secret, others do not. in some cases you may end up with a board or chip with no example code, just some data sheets and reference manuals.
if you want to get into this business though you need to be prepared to write this startup code (in assembler) that may call some C code to bring up the rest of the system, then that might start up the main operating system or application or whatever. Microcotrollers sounds like what you are playing with, the answers to your questions are in the chip vendors users guides, some vendors are better than others. search for the word reset or boot in the document to try to figure out what their boot schemes are. I recommend you use "dollar votes" to choose the better vendors. A vendor with bad docs, secret docs, bad support, dont give them your money, spend your money on vendors with freely downloadable, well written docs, with well written examples and or user forums with full time employees trolling around answering questions. There are times where the docs are not available except to serious, paying customers, it depends on the market. most general purpose embedded systems though are openly documented. the quality varies widely, but the docs, etc are there.
Depends completely on the controller/embedded system you use. The ones I've used in game development have the IP point at a starting address in RAM. The boot strap code supplied from the compiler initializes static/const memory, sets the stack pointer, and then jumps execution to a main() routine of some sort. Older systems also started at a fixed address, but you manually had to set the stack, starting vector table, and other stuff in assembler. A common name for the starting assembler file is CRT0.s for the stuff I've done.
So 1. You are correct. The microprocessor has to start at some fixed address.
2. The ISR can be supplied by the manufacturer or compiler creator, or you can write one yourself, depending on the complexity of the system in question.
3. The stack and initial programmer counter are usually handled via some sort of bootstrap routine that quite often can be overriden with your own code. See above.
Last: The steps will depend on the chip. If there is a power interruption of any sort, RAM may be scrambled and all ISR vector tables and startup code should be rewritten, and the app should be run as if it just powered up. But, read your documentation! I'm sure there is platform specific stuff there that will answer these for your specific case.
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I am already a software developer, but daily business work is neither challenging not improving my skills.
I have no clue how this embedded things work, what are the setup needs to be done to even run hello world program.
So I am looking for very basic development board, which is support at C language.
not very complicated or high processing. As that would be over killing for a just beginner.
if I am able to understand how to handle a small device. I would learn other upper level board. As it is self paced and self teaching. I don't wanna jump over a complicated board as that happened to me once. I have having LPC 21xx board, well equipped. having good space to create program and run them.
But I was knocked out in the round zero. could not figured out more then plugging into computer and turn it on.
So suggest me simple board it would be great if it support usb as my laptop does not have serial port. if if there is nothing no issue, I hope there will be something usb to serial. :)
Please help. I really wanna learn it.
The arduino is very user friendly but in part because they hid the stuff you are trying to learn. You can still get down to the metal on an arduino though
The winarm guy has tons of example programs to get you started.
Sparkfun is the place to go in the US for most boards. right now the sam7-h64 is on sale, atmel has a util for covering the loading of the board problem. you can get an mbed there, now the maple is there, coridium armmite pro, and a plethera of arduino variations. And the msp430 launchpad. No matter what I recommend picking up one of the msp430 launchpad boards, only $4.30, very nice architecture, the usb cable (that comes with it?) is all you need.
Another TI product is the stellaris line of cortex-m3 based chips/eval boards. The 811 is easy to brick, I would avoid it, comes with everything you need. the boards are dripping with goodies, oled display, buttons, etc.
At some point you are going to need to get your feet wet with openocd. Amontek makes the jtag-tiny which is a very nice arm jtag wiggler. A number of the eval boards have ftdi chips on them which handle usb to serial and usb to jtag, googling will show tons of info on how to use openocd to connect to and load.
Another path is qemu. a stellaris board/chip or few and other chip families are supported, so you can cover the learning to compile/build the program as well as program some peripherals without having to figure out the loading part.
The atmel avr butterfly is still available for $20. Three wires shoved into a serial port connector and you can program the thing. Has things on the board to learn to program, etc.
I recommend not limiting yourself to one processor family (avr, arm, msp430, etc) nor one chip vendor (lpc, atmel, ti, etc). many of these boards can be had for under $50, some under $25 (look at the ez430 additional boards 3 for $10, the launchpad might be able to program them, otherwise the ez430 is $20). (most of the arduino family wants an additional usb to serial plus power, which almost doubles the cost, also be careful to note 5V vs 3.3V boards, so you dont melt anything down, really good idea to get a few of the different ftdi usb to serial breakout boards from sparkfun anyway).
I don't know if you've heard of Arduino... it's a great beginning hardware platform, programmed with USB in C++. Boards are only $30 so it's pretty cheap too.
stm32l-discovery 14$ for stm32(16kb ram + 128kb flash + 4kb eeprom) + stlink2 on board, you just need an usb-cable. Be sure to get l version, not vl, the l- has slower cpu but an lcd and some touch sensitive buttons. I was a normal c developer before, but found a job in an embedded market, where we use the same processor. In a month I never used any assembler and the experience was not much different than programming for pc except for you can't effectively use dynamical allocation. But that doesn't matter, since you control all the memory and timing and all the hardware for that matter. The iar kickstart tools are also great, especially the debugger - it is fast and you can even attach to the running process. The editor in the IAR IDE sucks big time though. It still doesn't support unicode in 2011 and things like "outline" in eclipse. Still the IDE is very nicely integrated with the hardware. You also got stdperiph. library from stm. It is a bit on the bloatware side, but you can mix and match the modules you like or choose to use raw registers if it makes the code more readable or smaller. Anyway, ask away, if you are interested in my experience. I also would advise against avr, becaus from the cost/performance ratio they are much worse than stm. I was porting a lot of avr code in the last month(avr's had some supply problem) and even if the avr had 16 Mhz and the stm32 had only 32, it much faster, much more configurable and has more periferials which are also easier to programm. Cortex-M3 controller are much nearer to the PC you dont have to optimize alot and 32bit wide words for calculation will spare you much pain. M3 are more comfortable to program with the things like bit banding and configurable interrupt priorities.
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I would like to learn something about embedded development. I think the best thing would be to buy hardware stuff and play with it but I don't know where to start and, if possible, I would like not to pay too much....
If you have experience in this field, which would be the best road to follow?
I assume you mean real embedded and not embedded linux or some other operating system thing.
All above are good, sparkfun.com is a GREAT resource for sub $50 cards. Dont buy the embed. The armmite pro is nice, trivial to bypass the high level canned package and load your own binaries (I have a web page on how to do it if interested).
Stellaris is good, the 811 is easy to brick so be careful, the 1968 eval board is not a bad one. The problem with the stellaris boards is almost all of their I/O is consuemed by on board peripherals. The good thing about the stellaris eval boards, based on what you are wanting to do is that all the I/O is consumed by on board peripherals. Lots of peripherals for you to learn how to write embedded code for.
You are going to eventually want a jtag wiggler, I recommend the amontec jtag-tiny, it will open the door to a number of the olimex boards from sparkfun. the sam7 and stm32 header boards are good ones as well.
the lillypad is a good starting place for arduino (sparkfun), same price as the arduino pro mini, but you dont have to do any soldering. get a lillypad and the little usb to serial thing that powers it and gives you serial access to program it. Just like the armmite pro I have a web page on how to erase the as-shipped flash and have a linux programmer that lets you load any binary you want not just ones limited to their sandbox.
avoid PIC and 8051 unless you are interested in a history lesson. the PIC32X, not sure my first one is in the mail, it is a MIPS 32 not a PIC core.
the ez430 msp430 board is a very good one, the msp430 has a very nice architecture, better than the avr.
You can get your feet wet in simulation as well. I have a thumb instruction set emulator, thumbulator.blogspot.com. Thumb is a subset of the arm instruction set and if you learn thumb then you can jump right into a stellaris board or stm32. My sim does not support thumb2, the thumb2 processors also support thumb, the transition to thumb2 from thumb is trivial.
avoid the stm32 primer boards, avoid the stm32 primer boards, avoid the mbed2 boards, avoid the mbed2 boards, avoid the lpcxpresso boards, avoid the lpcxpresso boards!!
I recently found a behavioral model of an arm in verilog that you can simulate your programs, have not played with it much. qemu-arm is probably easier, not a bad place to get your feet wet although it can be frustrating. Which is why I wrote my own.
ARMS own armulator is out there, in the gdb source release for example, easier than qemu-arm to use, but can be frustrating as well.
go to codesourcery for arm gcc tools. use mspgcc4.sf.net for msp430 tools. llvm is rapidly catching and passing gcc, if nothing else I expect it to replace gcc for the universal cross compiler tool. at the moment it is much more stable and portable than gcc when it comes to building for cross compiling (because it is always/only a cross compiler wherever you find or use it). the msp backend for llvm was an afternoon experiment for someone, sadly, I would really like to have that supported. If you use llvm, use clang not llvm-gcc.
If you want to get your feet wet, get a cheap evaluation board like Stellaris LM3S811 Evaluation Kit (EK-LM3S811) which is $50 at Digi-Key then download CodeSourcery G++ which provides free command line tools or the IAR Kickstart Edition which allows you up to 32KB of code.
I would suggest starting up with MSP430. The MSP430 launchpad is quiet cheap. Alternatively, you could start up with the Stellaris (ARM Cortex M3) Boards. You can use the already provided libraries first to start developing apps rite away and then start writing your code for configuring and getting things done by referring the data sheet.You also get example codes, relevant documents and Keil 32K limited evaluation version. If you want to do things write from scratch, then get an ARM based board with IO breakout headers and start working. Lot of them are available from vendors like Olimex. One word of caution ARM is difficult to start with if you are working from scratch with little or no idea about embedded. So if you are looking for something easier go for AVR or 8051, but 8051 core is too old. So, Stellaris would be a good option in my opinion with their already available driver libs and codes.
Well, depending how much money you want to spend, and how much development expertise you have, you could either get an Arduino (arduino.cc) or a FEZ Domino (C# .NET) (tinyclr.com). Both are premade MCUs, with all the tools you need to start developing out of the box.
The Arduino is going to be very simplistic, but probably better for a beginner. The FEZ is a little harder to work with, but FAR more capable. Both have the same physical pinout, so you can use "shields" between them
I would recommend a kickstart kit from iar systems. They're fairly complete and work out of the box.
http://www.iar.com/website1/1.0.1.0/16/1/
As a hobby project to keep myself out of trouble, I'd like to build a little programmer timer device. It will basically accept a program which is a list of times and then count down from each time.
I'd like to use a C or Java micro controller. I have used BASIC in the past to make a little autonomous robot, so this time around I'd like something different.
What micro controller and display would you recommend? I am looking to keep it simple, so the program would be loaded into memory via computer (serial is ok, but USB would make it easier)
Just use a PIC like 16F84 or 16F877 for this. It is more than enough.
As LCD use a 16 x 2 LCD. It is easy to use + will give a nice look to your project.
LCD
The language is not a matter. You can use PIC C, Micro C or any thing you like. The LCD's interface is really easy to drive.
As other components you will just need the crystal and 2 capacitors as oscillator + pull up resister. The rest of the components depend on the input method that you are going to use to set the times.
If you are using a computer to load the list then you will need additional circuit to change the protocols. Use MAX 232 to do that. If you want to use USB, you need to go ahead and use a PIC with USB support. (18F series)
(source: sodoityourself.com)
This is a set of nice tutorials you can use. You can purchase the products from them as well. I purchased once from them.
I would go with the msp430. An ez430 is $20 and you can get them at digikey or from ti directly, then sets of 3 microcontroller boards for $10 after that. llvm and gcc (and binutils) compiler support. Super simple to program, extremely small and extremely low power.
There are many ways to do this, and a number of people have already given pretty good suggestions AVR or PIC are good starting points for a microcontroller to work with that doesn't require too much in the way of complicated setup (hardware & software) or expense (these micros are very cheap). Honestly I'm somewhat surprised that nobody has mentioned Arduino here yet, which happens to have the advantage of being pretty easy to get started with, provides a USB connection (USB->Serial, really), and if you don't like the board that the ATMega MCU is plugged into, you can later plug it in wherever you might want it. Also, while the provided programming environment provides some high level tools to easily protype things you're still free to tweak the registers on the device and write any C code you might want to run on it.
As for an LCD display to use, I would recommend looking for anything that's either based on an HD44780 or emulates the behavior of one. These will typically use a set of parallel lines for talking to the display, but there are tons code examples for interfacing with these. In Arduino's case, you can find examples for this type of display, and many others, on the Arduino Playground here: http://www.arduino.cc/playground/Code/LCD
As far as a clock is concerned, you can use the built-in clock that many 8-bit micros these days provide, although they're not always ideal in terms of precision. You can find an example for Arduino on doing this sort of thing here: http://www.arduino.cc/playground/Code/DateTime. If you want something that might be a little more precise you can get a DS1307 (Arduino example: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1191209057/0).
I don't necessarily mean to ram you towards an Arduino, since there are a huge number of ways to do this sort of thing. Lately I've been working with 32-bit ARM micros (don't do that route first, much steeper learning curve, but they have many benefits) and I might use something in that ecosystem these days, but the Arduino is easy to recommend because it's relatively inexpensive, there's a large community of people out there using it, and chances are you can find a code example for at least part of what you're trying to do. When you need something that has more horsepower, configuration options, or RAM, there are options out there.
Here are a few places where you can find some neat hardware (Arduino-related and otherwise) for projects like the one you're describing:
SparkFun Electronics
Adafruit Industries
DigiKey (this is a general electronics supplier, they have a bit of everything)
There are certainly tons more, though :-)
I agree with the other answers about using a PIC.
The PIC16F family does have C compilers available, though it is not ideally suited for C code. If performance is an issue, the 18F family would be better.
Note also that some PICs have internal RC oscillators. These aren't as precise as external crystals, but if that doesn't matter, then it's one less component (or three with its capacitors) to put on your board.
Microchip's ICD PIC programmer (for downloading and debugging your PIC software) plugs into the PC's USB port, and connects to the microcontroller via an RJ-11 connector.
Separately, if you want the software on the microcontroller to send data to the PC (e.g. to print messages in HyperTerminal), you can use a USB to RS232/TTL converter. One end goes into your PC's USB socket, and appears as a normal serial port; the other comes out to 5 V or 3.3 V signals that can be connected directly to your processor's UART, with no level-shifting required.
We've used TTL-232R-3V3 from FDTI Chip, which works perfectly for this kind of application.
There are several ways to do this, and there is a lot of information on the net. If you are going to use micro controllers then you might need to invest in some programming equipment for them. This won't cost you much though.
Simplest way is to use the sinus wave from the power grid. In Europe the AC power has a frequency of 50Hz, and you can use that as the basis for your clock signal.
I've used Atmel's ATtiny and ATmega, which are great for programming simple and advanced projects. You can program it with C or Assembly, there are lots of great projects for it on the net, and the programmers available are very cheap.
Here is a project I found by Googling AVR 7 segment clock.
A second vote for PIC. Also, I recommend the magazine Circuit Cellar Ink. Some technical bookstores carry it, or you can subscribe: http://www.circellar.com/
PIC series will be good, since you are creating a timer, I recommend C or Assembly (Assembly is good), and use MPLAB as the development environment. You can check how accurate your timer with 'Stopwatch' in MPLAB. Also PIC16F877 has built in Hardware Serial Port. Also PIC16F628 has a built in Hardware serial port. But PIC16F877 has more ports. For more accurate timers, using higher frequency oscillators is recommended.
In the last two months I've worked as a simple application using a computer vision library(OpenCV).
I wish to run that application directly from the webcam without the need of an OS. I'm curious to know if that my application can be burned into a chip in order to not have the OS to run it.
Ofcorse the process can be expensive, but I'm just curious. Do you have any links about that?
ps: the application is written in C.
I'd use something bigger than a PIC, for example a small 32 bit ARM processor.
Yes. It is theoretically possible to port your app to PIC chips.
But...
There are C compilers for the PIC chip, however, due to the limitations of a microcontroller, you might find that the compiler, and the microcontroller itself is far too limited for computer vision work, especially if your initial implementation of the app was done on a full-blown PC:
You'll only have integer math available to you, in most cases, if not all (can't quote me on that, but our devs at work don't have floating point math for their PIC apps and it causes many foul words to emanate from their cubes). Either that, or you'll need to hook to an external math coprocessor.
You'll have to figure out how to get the PIC chip to talk USB to the camera. I know this is possible, but it will require additional hardware, and R&D time.
If you need strict timing control,
you might even have to program the
app in assembler.
You'd have to port portions of OpenCV to the PIC chip, if it hasn't been already. My guess is not.
If your'e not already familiar with microcontroller programming, you'll need some time to get up to speed on the differences between desktop PC programming and microcontroller programming, and you'll have to gain some experience in that. This may not be an issue for you.
Basically, it would probably be best to re-write the whole program from scratch given a PIC chip constraint. Good thing is though, you've done a lot of design work already. It would mainly be hardware/porting work.
OR...
You could try using a small embedded x86 single-board PC, perhaps in the PC/104 form factor, with your OS/app on a CF card. It's a real bone fide PC, you just add your software. Good thing is, you probably wouldn't have to re-write your app, unless it had ridiculous memory footprint. Embedded PC vendors are starting to ship boards based on 1 GHz Intel Atoms, and if you needed more help you could perhaps hook a daughterboard onto the PC-104 bus. You'll work around all of the limitations listed above, as your using an equivalent platform to the PC you developed your app on. And it has USB ports! If you do a thorough cost analysis and if your'e cool with a larger form factor, you might find it to be cheaper/quicker to use a system based on a SBC than rolling a solution using PIC chips/microcontrollers.
A quick search of PC-104 on Google would reveal many vendors of SBCs.
OR...
And this would be really cheap - just get a off-the-shelf cheap Netbook, overwrite the OEM OS, and run the code on there. Hackish, but cheap, and really easy - your hardware issues would be resolved within a week.
Just some ideas.
I think you'll find this might grow into pretty large project.
It's obviously possible to implement a stand-alone hardware solution to do something like this. Off the top of my head, Rabbit's solutions might get you to the finish-line faster. But you might be able to find some home-grown Beagle Board or Gumstix projects as well.
Two Google links I wanted to emphasize:
Rabbit: "Camera Interface Application Kit"
Gumstix: "Connecting a CMOS camera to a Gumstix Connex motherboard"
I would second Nate's recommendation to take a look at Rabbit's core modules.
Also, GHIElectronics has a product called the Embedded Master that runs .Net MicroFramework and has USB host/device capabilities built-in as well as a rich library that is a subset of the .Net framework. It runs on an Arm processor and is fairly inexpensive (> $85). Though not nearly as cheap as a single PIC chip it does come with a lot of glue logic pre-built onto the module.
CMUCam
I think you should have a look at the CMUcam project, which offers affordable hardware and an image processing library which runs on their hardware.