Getting into Embedded [closed]

Question

I'm trying to familiarize myself with the embedded field, but also have limited resources in terms of time and equipment to buy.

• What's a good language to wrap my head around embedded, without investing too much time leaning an embedded-specific language? I'm most familiar with PHP, Java, Actionscript, but unfortunately know very little C. I remember reading somewhere that someone used PERL to program embedded systems, but not sure if that's really possible.

• Can learning be done without needing to buy chips, etc. via simulators or such?

• Can someone recommend a simplified roadmap to show how one would get sarted? I'm a little unsure where to even start.

Answer 1

You need to know C (but every programmer needs to know C !)

Most of these platforms have a simulator/emualtor, but since the point is to learn real applications and real problems ( which are all to do with real world timing issues) then you want a real board.

You probably also want an oscilloscope (a very cheap n'th hand slow analogue scope will do) and have some idea how to use it.

Easiest way in is probably Arduino, perhaps more professional but a little harder is launchpad MSP430

Answer 2

There are a few embedded programming lessons that carry over from one platform and style to another, but it is really a broad field. Different processors can require very different tactics, and different applications can dictate both different firmware design tactics and different microcontrollers. Here's some stuff to get you started....

msp430

Texas Instruments has several very inexpensive USB development kits which they call EZ430 and are based on their MSP430 family of micro-controllers. The simplest one has an msp430 f2013, which has 2K of flash program space, 3x128 bytes of usable user flash (another 128 byte page exists, but it's special), 128 bytes of RAM (yes, 128 bytes but it's enough for lots of things), and 16 CPU registers (some of these are special purpose like the Stack Pointer, Instruction Pointer, Status Register, and maybe one or two more). MSP430s also have several memory mapped special function registers which are used for configuring and controlling the built in peripherals. MSP430s are von Newman processors, so everything lives within one address space. These cost about $20us for both the programmer and a removable tab (pc board) containing the msp430 f2013. For about $10us you can get 3 replacement tabs with msp430 2012, which is pin compatible with the 2013 (mostly) and has a few different peripherals. These tabs have an LED, a button, and several large vias (holes in the pc board) which are connected to the pin of the processor. These vias are easy to solder wires into even if you have never soldered before -- due to capillary action the vias just suck the molten solder up and while it's hot you can just jab the end of your wire in there.

They also have a couple more similar kits with 802.15.4 radios. Even if you aren't interested in the radio you may still be interested in these because their programmer also has a UART pulled over from the removable tab and are compatible with the tabs used on the other kits mentioned above. These kits also contain at least one extra programmable board and a battery pack for it. (one of these kits may contain more, but I don't have mine with me right now, and not going to look it up).

They also have a kit that has a programmable watch as the target platform. I've never had one of these, but they have a display, accelerometers, and several other cool things, but this may overwhelm you for your first project. I'd suggest one of the previous kits to get you started with MSP430s.

You can get free C compilers and development environments for MSP430s in the form of IAR's Embedded Workbench kickstart (4 kb program space limited ) IDE, Code Composer Studio (also limited program size, but higher limit, I think), and gcc/gdb for the MSP430. IAR's kickstart is pretty easy to get started with quickly, though it's not perfect. You may find that you have to shut it down, unplug your USB EZ430, restart IAR, and plug back in to get it going again. Or maybe some different order will work better for you.

TI also provides many examples in badly named files (all of their downloadable files go out of their way to be badly named). Be warned -- similar MSP430s may have different device control register interfaces for similar peripherals, which can be confusing. Make sure that any document or example you are reading really does apply to the microcontroller you are using.

other small systems

There are many many other processors families and kits that you can go with, and you should probably at least know a little bit about them.

AVR -- Atmel's 8/16 bit Harvard architecture. Harvard refers to separate address spaces for code and working memory. It has 32 8 bit registers, some of which may be used in pairs as 16 bit registers. It's a very popular and pretty cool processor. Some of the smallest ones only have registers with no extra RAM, which is scary. Atmel also has an AVR32 which isn't at all the same as the AVR. Unless you make use of an existing bootloader capable of loading your new code you will need to get a JTAG unit for these.

8051 -- This is old as the hills and a pain in the butt to use until you finally understand it. It is an 8/16 bit processor, with many more limits on how you go about doing 16 bit math and only has 1 pair of registers which can act as a pointer. It has 3 separate address spaces (stack, global memory, and code) and lots of odd (compared to other architectures) features. The low level stuff might not mean much to you if your are programming in C except that very simple C operations can turn into much more code than you thought they would. You don't want to start on one of thise, most likely.

propeller -- Parallax's very interesting multi-core processor which is very unlike other processors. It has several cores which act mostly independently and can be used to simulate peripherals or do more traditional computational tasks. I've never used one of these, though I'd like to. Just never had a task that seemed to fit it. They have their own high level language to program them as well as the processor's assembly language.

larger systems

After you get out of the 8/16/24 bit processors you start to blur the lines between embedded and desktop level programming, even if it is technically embedded.

AVR32 -- There are 2 main versions of these. One is a Harvard architecture and the other is von Newman. The von Newman version is essentially a better ARM than ARM, but it's not as popular as ARM. As near as I can tell it was designed with "run Linux" in mind, though not tied to it in any crazy way. You used to be able to get cheap development boards for these and code is often almost as easy to load as copying files from one PC to another, though you will probably make use of uboot and tftp to do some work. JTAG is only needed when you mess up the boot loader. I think all of these have support for native JAVA acceleration. www.AVR32.org

ARM -- The most popular embedded processor. There's many versions of these. Some don't have an MMU (memory management unit) and some do. There's too much to say about them. Some version have native JAVA acceleration, though I think that the ARM lords don't freely tell all of the details of how to use it, so you have to find a JVM which knows how to use it. Many vendors make them, including Atmel, Freescale, Intel, and many others.

MIPS -- A very RISC processor. The RISCiest.

There are many others.

Programming styles

I could write 3 books on this but the general rule is make things as simple as the application can let you. An exception to this is that if you can easily make use of an operating system you might want to make use of it if it simplifies your task.

Answer 3

The first thing you need to know when answering this question is "WHAT IS" an embedded system? A GENERAL definition would be a computer system which is dedicated to a single specific purpose. This doesn't limit the type of hardware you can use, as matter of fact "Embedded PCs" have been used for years. The QNX realtime OS has existed since the early 80s and been used in industrial PCs for embedded applications for years. I've personally used in control systems for steel mills XRAY thickness gages. On the other hand I currently use TI DSPs without any OS support and only using 256K of Ram. Another example would be the key fob for your car. Old ones used to use a PIC microcontroller from Microchip. (That's actually the company's name.)

Some people call the IPhone an embedded system, but due to the fact you can load applications to do just about anything I tend to say it's a palm top computer with phone capabilities. An OLD DUMB cell phone that is just a phone, not PDA is an embedded system. That's just a bit of philosophy.

As a general rule there are a handful of concepts you need to grasp for embedded systems programming, and most of them can be explored on a PC.

EDIT: The REASON why C or C++ is recommended is C itself was designed to do systems programming. C++ maintains all it's advantages but adds capabilities for OOP programming. Some ASM maybe required in some systems. However a lot of chip vendors, such as TI, provide tools basically make it possible to do your entire system in C++. :END EDIT

ALOT of simple embedded systems look more or less like this:

While(true) // LOOP FOREVER... There is no command prompt
{
  // Typically you want I/O to occur on fixed "timebase."
  wait(timerTick);
  readDigitalIO(&dioStruct);
  readAnalogIO(&aioStruct);

  // Combine current system state with input values
  // and do some useful calculations.  (i.e. Analog input to temperature calc)
  Process(dioStruct,aioStruct,&CurrentState);

  // This can be a serial output/audio buzzer/leds/motor controller
  // or Whatever the system REQUIREMENT call for.
  driveOutputs(CurrentState);

  // The watchdog timer resets your system if it gets stuck.
  petWatchDogTimer();
}

There is nothing here that you can't do using the PC. (Well a PC that still has a parallel port anyway. Which is a more or less just a DIO port.) On a simple system without a os this might be all there is. On a RTOS based system you may have several task that all look somewhat simalar to this, but pass data back and forth between the tasks.

The interesting parts come when you have to interface to the hardware on you're own, the first job I had out of college was writing a device driver for a data acquisition board under QNX.

Basic concepts of dealing with hardware, or device drivers (Which you can experiement with by hacking Linux device drive code which is freely avaliable.), most hardware looks to the programmer like just another memory address. This is called "Memory mapped I/O." What does this mean? Lets use a serial port as an example:

// Serial port registers definition:
typedef struct  
{
   unsigned int control;  // Control bits for the port.
   unsigned int baudDiv;  // Baud rate divider.
   unsigned int status;   // READ Status bits/ Write resets fifos;
   char TXdata;           // The head of the hardware TX fifo.
   char RXdata;           // The tail of the hardware RX filo.
} serRegs;
// Using the volatile keyword to indicate the hardware can change the value
// independantly from the software.
volatile serRegs *Ser1 = (serRegs *)0x8000;  // Hardware exists at a specific location in memory.
volatile serRegs *Ser2 = (serRegs *)0x8010;  // Hardware exists at a specific location in memory.

// Bits bits 15-12 enable interupts and select interupt vector,
//      bits 11-8 enable,bits 7-4 parity,bits 3-0 stop bits.
Ser1->status = 1; // Reset fifos.  
Ser1->baudDiv = CLOCKVALUE / 9600;  // Set the baudrate 9600;
Ser1->control = 0x1801; // Enable, 8 data, no parity, 1 stop bit.
// Write out a "OK\r\n" message; (Normally this would be a loop.)
Ser1->Txdata = 'O';  // First byte in fifo Transmission starts.
Ser1->Txdata = 'K';  // Second byte in fifo still transmitting first byte
Ser1->Txdata = '\r'; // Third byte in fifo still transmitting first byte
Ser1->Txdata = '\n'; // Fouth byte in fifo still transmitting first byte

Normally you would have a function or an interrupt handler to handle TXing the data, but for example I wanted to point out that the hardware is working while the software keeps going. Basically hardware works like, I write a value to an address and "STUFF" happens independantly of the software. This is perhaps one of the key concepts for embedded programming, how to make the computer effect a change in the real world.

EDIT:

If you actually want to get a cheap board, the current trend from Micro developers is to put a dev kit on a usb thumb stick. This page has info on several, ranging from 8 bits upto ARM architectures: http://dev.emcelettronica.com/microcontrollers-usb-stick-tool

The Cypress PSOC was one of the first to do this with the "FirstTouch Starter Kit." The PSOC is a very unique part in that it has a micro controller and "Configurable analog and digital blocks" that allow you to plop down a ADC, serial port, or digital I/O using a gui and automatically configures you're C app to use it. The PSOCs also are avaliable in DIP packages which makes them easy to use on a prototyper's breadboard.

Answer 4

Picture your embedded controller sitting in a switched-off circuit...

1. The Vcc power is applied and the reset circuit asserts reset signal.

2. Clocks have reached running speeds and voltages stabilized, so reset is de-asserted.

3. Now your controller sets its instruction pointer to the "reset vector," which is physical address 0xE0000000 on this particular chip. The controller fetches the instruction at that location.

4. Interrupts are disabled, and the first order of business is to initialize registers such as the stack pointer. On some chips, there are flags bits (e.g., x86 direction flag) which need to be cleared or set.

5. Once the registers and flag bits are set up correctly, it becomes possible for interrupt service routines to run. By now, we must have run code to about location 0xE0000072 when we get to the code which enables interrupts by first toggling some GPIO pins to the external interrupt controller, then enables the CPU interrupts mask.

6. At this point, the equivalent of "device drivers" are running in the form of interrupt service routines. Assuming the C environment has a library which matches the interfaces of these routines' data structures, by now our boot-loader code can jump to the main() function of some C object code.

In other words, the code which brought us from power-on to main(), and which handles the low-level I/O, is written in the assembler peculiar to the chip you choose. This means that if you want to be versatile at embedded programming, you must know how to implement assembly code starting at the reset vector.

The reality is that hobbyist embedded programming doesn't allow time for implementing all the ISRs and the boot-loader code. For this reason, many people use standard software frameworks available for specific chips. Others use custom-language chips such as the BASICstamp. The BASICstamp is an embedded chip which hosts a BASIC language interpreter on-board. The interpreter and all the ISRs are pre-written for you. The BASIC environment gives you the ability to control I/O pins, read voltages, everything you could do from assembly with an embedded controller, but a bit slower.