Due to the current chip shortage, I have had to purchase PIC microcontrollers that have a different specification to what was initially designed.
Initial: PIC24FJ256GA606
Revision 1: PIC24FJ512GA606
Revision 2: PIC24FJ1024GA606
In this instance, the microcontrollers are within the same family but have different size of memory.
Initially, the binary was created to support multiple product variants and they all use this microcontroller (using hardware pins to define the type of product and thus the software features it supports). I would like to continue with a single binary but to be able to support the different microcontrollers specified above.
We flash the microcontrollers using a PICKIT 4 during manufacturing.
A custom bootloader is also flashed onto the microcontroller during manufacturing to allow the firmware update procedure to be is driven by another PIC microcontroller out in the field (it's a distributed system connected by RS-485).
I use MPLAB X IDE for development and buildings production binaries.
I guess the key question is about if this is even possible?
If so, then how would I achieve creating the single binary that supports multiple processors?
Normally a single binary should only correspond to the specific controller. Because especially Microchip has really wide variaty of microcontrollers. But as you mentioned in your question:
In this instance, the microcontrollers are within the same family but have different size of memory.
You can slightly use the same binary as long as you select the hardware very carefully. I mean if those 3 different models has the same pin mapping but some has less or some has more, then you would select the common corresponding pins for the I/O functions wherever possible. Since those devices are from the same family they must have common IO pins with the same port and pin numbering.
If those similarities including of that the internal registers are enough for the functionality of your system, you can use the same binary for those 3 or more devices as long as you select the right hardware very carefully and none of the functions remain without touching its hardware.
But it is very hard to say the same for the others that are not belong to a series in the same family. In this case you can check the hardware similarities for each functionality of your system. If that micro provides the same hardware, then you can go and firstly give it a try to see whether it will be programmed and then it will funtion in the same way. After making sure enough you can add that model in your usable models list, too.
Hope this give you a helpful idea.
For two microcontrollers to have compatible binaries, they need to fulfil the following:
The CPU cores must have identical Instruction Set Architecture. Be aware that the term "code compatible" by the manufacturer might only mean that two parts have the same ISA and are compatible on the assembly language level, as long as no peripherals or memories are used...
In case they have different memory sizes, the part with larger memory must be a superset of the part with smaller memory and they must map memory to the same addresses.
All hardware peripherals used must be identical and any peripheral routing registers used must also be identical. Please note that the very same core of the same family but with a different package and pin routing might mean that peripheral routing registers must be set differently.
There can be no check of MCU partnumber registers etc inside the firmware, nor can there be any in the flash programming equipment.
In general this means that the MCUs must be of the very same family and the manufacturer must guarantee that they are replaceable.
You can very likely switch between different temperature spec parts of the same model and between automotive/non-automotive qual parts of the same model without changing the code.
First : This Question have a duplicate here :
How does a modern operating system like Windows or Linux know the chipset specific memory map?
But the answer in this Question is speaking about device tree and ACPI (for legacy PCs) without the details I need to write an assembly or c code to utilize the information in ACPI tables, I am now trying to learn about legacy pc first and how to decode the tables of the ACPI , I tried doing some search and I found that the most important table is the DSDT , Now my questions How to decode the information in the table to get a detailed memory map (ranges) and also to get which devices are connected to the CPU and how to get the address of the DSDT in memory ? , I tried doing some search but I couldn't understand the AML language which i think is related to this subject .. I will be helpful if any one elaborate and provide good material for understanding ACPI tables and decoding them for beginners , The problem for me I couldn't have a standard fixed memory map in mind because i want to know how the same os version run on different chipsets , there must be a dynamic way to detect the whole map , so a suggested process for getting the whole map is also another question of me
please note also this is my first step toward learning how to communicate directly with bare metal hardware devices each individually (which is the second step)
Thanks
Let's split this into 3 different problems.
How to get the address of the DSDT in memory?
The firmware provides a pointer to (one or 2) ACPI tables that contain an index of all other tables. These tables are the RSDT (Root System Descriptor Table) and XSDT (Extended Root System Descriptor Table); and the only real difference between them is that the XSDT supports 64-bit addresses (and should be used if possible) while the older RSDT does not (and should be considered "deprecated" and only used as a fallback for modern 64-bit operating systems). These tables mostly provide the identifier and address of all other tables; so if you want to find a specific table (e.g. the DSDT) you can search the index for the identifier (e.g. the 4 ASCII characters "DSDT") and find the entry that contains the table's physical address.
The pointer/s to the index are contained in a special structure called the RSDP (Root System Description Pointer); which is found in different ways for different types of firmware. For BIOS you have to search a few specific areas of physical memory looking for a special structure (with a special signature, and a valid checksum); and for UEFI you simply ask the firmware (and avoid a "cache pounding" search).
This is all (relatively clearly) described by the ACPI specification, including how to find the RSDT (e.g. the section "Root System Description Pointer (RSDP)"), and including the format of all structures and tables, and the meaning and purpose of all fields.
How to decode the information in the DSDT?
Because things can change after boot (due to hot-plug support, etc); static tables can't be used for some things and ACPI solves this problem (and creates more problems) by defining a special language called ASL (ACPI Assembly Language) that is compiled into a portable byte-code called AML (ACPI Machine Language).
The DSDT contains this AML.
To make any sense of it you need an AML interpreter, to execute the AML that is contained in the DSDT.
This is "very challenging" - to do it yourself you'll probably need to spend months studying the ACPI specification (and years working around bugs in different computers). Most people port an open source implementation (originally created by Intel) that is called ACPICA (see https://acpica.org/ ).
Sadly; being able to execute AML is only the first step. You also need to understand ACPI's namespaces, which functions/methods are provided by the AML and what they're supposed to do. To make this worse; ACPI's AML expects to be informed of what the OS is, and then enables/disables various features and changes its behavior to suit the OS (depending on what it was told the OS is); and often the only operating systems that are recognized by AML are versions of Windows and if you tell it something else it disables various features, so most operating systems just lie and say they are a version of Windows so that AML doesn't provide a crippled subset of its capabilities. However; "what each version of Windows does" (and how AML behaves for each specific version of Windows) is a horrible undocumented (by ACPI specs) disaster. Fortunately; ACPICA also hides the majority of this pain (for people that port ACPICA).
How to get a detailed memory map (ranges) and also to get which devices are connected to the CPU?
Mostly you don't. Specifically, you don't just "get a detailed memory map" in a nice single step.
Instead; you start by getting some minimal information about the physical memory from firmware (from int 0x15, eax=0xE820 for BIOS, or from GetMemoryMap() on UEFI). Then you use a variety of different sources to add more details to that minimal information, including but not limited to the CPUID instruction (for how many bits a physical address actually has), the ACPI "APIC/MADT" table (for IO APIC and local APIC addresses), the ACPI "EDT/HPET" table (for HPET addresses), the ACPI "MCFG" table (for the addresses of PCI Express memory mapped configuration space areas), the ACPI "SRAT" table (for NUMA information for memory areas and "hot-plug RAM" information), and possibly (optionally) the SMBIOS tables (if you care about things like what type of RAM is installed, etc).
After obtaining all the information you want from static/unchanging sources; you switch to "phase 2", which involves continually managing the memory map and trying to keep it up to date as information from various devices is found (and modified via. hot-plug events). This is where being able to execute AML (from DSDT, using your AML interpreter) becomes important. It also involves bus specific approaches (e.g. scanning PCI buses and extracting information from each PCI device's BARs/Base Address Registers).
Note that this isn't purely about filling in details for the memory map. It's better to thing about it as discovering the resources that devices use, which includes IO ports, IRQ lines, DMA channels (and not just areas of the physical address space alone).
Also note that you only really information about devices if/when you have a device driver that is capable of using the information to "drive" the device. If you don't, then the memory map you have will just say "reserved" and you won't know why, but you probably won't have a reason to care why anyway.
Final Note
This is "very daunting" at first glance. Don't be worried - you can (and should) start small and ignore most of it until much much later. You can do a lot with the minimal information about the physical memory from firmware alone; and add code to do almost everything else if/when it actually matters for your OS one day.
I'd like to write some C code be able to query processor attributes on PowerPC, much like one can do with cpuid on x86. I'm after things like brand, model, stepping, SIMD width, available operations, so that there can be run-time confirmation that the code is being used on a compatible platform before something blows up.
Is there a general mechanism for doing this on PowerPC? If so, where can one read about it?
Note that PowerPC has not dozens of extensions / features like x86. It is required to read specific privileged registers that may depend on cores.
I checked on Linux and you can access PVR, there is a trap in the kernel to manage that.
Reading /proc/cpuinfo can return if Altivec is supported, the memory and L2 cache size ... but that is not really convenient.
A better solution is described here:
http://www.freehackers.org/thomas/2011/05/13/how-to-detect-altivec-availability-on-linuxppc-at-runtime/
That uses the content of /proc/self/auxv that provides "the ELF interpreter information passed to the process at exec time".
The example is about Altivec but you can get other features (listed in include "asm/cputable.h"): 32 or 64 bit cpu, Altivec, SPE, FPU, MMU, 4xx MAC, ...
Last, you will find information on caches (size, line size, associativity, ...), look at files in:
/sys/devices/system/cpu/cpu0/cache
PowerPC doesn't have an analogue to the CPUID instruction. The closest you can get is to read the PVR (processor version register). This is a supervisor-privileged SPR, though. However, some operating systems, FreeBSD for example, will trap and execute that for user space processes.
The PVR is read-only, and should be unique for any given processor model and revision. Given this, you can ascertain what features are provided by a given CPU.
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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.
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
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.
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.
Picture your embedded controller sitting in a switched-off circuit...
The Vcc power is applied and the reset circuit asserts reset signal.
Clocks have reached running speeds and voltages stabilized, so reset is de-asserted.
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.
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.
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.
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.
As for the language, C is probably the most important language to know. From Java you should be able to adapt, but just remember that a lot of high level Java will not be available to you. Loads of textbooks out there but I'd recommend the original C programming book by Kernighan and Ritchie http://en.wikipedia.org/wiki/The_C_Programming_Language_(book)
For a good introduction to embedded C you could try a book by Michael J Pont:
http://www.amazon.com/Embedded-C-Michael-J-Pont/dp/020179523X
As for the embedded side of things you could start with Microchip, the IDE is OK to develop in with a reasonable simulator, and the c compilers are free for the slightly limited student editions c18 and c30 compilers, the IDE installer will also ask if you want to install a 3rd party HI-TECH C compiler which you could use. As for the processor I'd recommend selecting a standard 18 series PIC such as the PIC18F4520.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en019469&part=SW007002
Whatever the chip manufacturer, you have to get to know the datasheets. You don't have to learn it all at once but will need it to hand!
Embedded, like most programming, tends to revolve around:
1) initialising a resource, in this case rather than data being from a data store it is from computer registers. Just include the processor header file (.h) and it will allow you to access these as ports (usually bytes) or pins (bits). Also micro-processors come with useful resources on the chip such as timers, analogue to digital converters (ADCs) and serial communications systems (UARTs). Remember that the chip itself is a resource and needs initialising before anything else.
2) using the resource. C will allow you to make data as global as possible and everything can access everything at every time! Avoid this temptation and keep it modular like Java will have encouraged you to (though for speed you may need to be a little looser on these rules).
But they do have an extra weapon called interrupts which can be used to provide real-time behaviour. These can be thought of a bit like OnClick() events. Interrupts can be generated by external events (e.g. buttons or receiving a byte from another device) and internal (timers, transmissions completed, ADC conversions completed). Keep interrupt service routines (ISRs) short and sweet, use them to handle real-time events (e.g. take a byte received and store it in a buffer then raise a flag) but allow background code to deal with it (e.g. check a received byte flag, if set then read the byte received). And remember the all important volatile for variables used by ISR routines and background routines!
Anyway, read around, I recommend www.ganssle.com for advice in general.
Good luck!
The scope of embedded computing has grown very broad, so the answers somewhat depend on what kind of device you're aiming at. On one end, there are 8-bit controllers with only a few KB of memory, usually programmed entirely in assembly or C. On the other end, processors such as those in your router are fairly powerful (200 MHz and a few MB of RAM is not uncommon) and often run an OS like Linux, which means you can use pretty much any language, though C and Java are the most common.
It's best to buy a real chip and experiment. Most of the work involved is usually in getting to know a device and how to interface with it, so using a simulator kind of defeats the purpose.
What's a good language to wrap my head around embedded, without investing too much time leaning an embedded-specific language?
As everyone will suggest: C. Now depending on how deep are you going to dig into your platform of choice, you may also need some assembly, but don't be scared about that: typically you'll use just a little.
If you are learning C, my personal suggestion is: work as you would do in assembly; the programming language won't give you much abstractions, so think in terms of memory management. When you've learnt how to do it move up towards abstractions and live happy.
C++ is also popular on embedded platforms, but IMHO is difficult unless you know well how to program in C you can also understand what's under the hood of its abstraction.
When you feel confident with C/C++ you can start to mess with embedded operating systems. You'll notice that they can be totally different from your OS of choice (By example not all operating systems have a C standard library, processes and splitting between userspace and kernelspace).
You'll learn how to build a cross compiler, how to mess with linker scripts, the tricks of binary formats and a lot of cool stuff.
For the theoretical point of view there's a lot of stuff as well: if you study Computer Science you can get a master's degree in embedded systems.
Can learning be done without needing to buy chips, etc. via simulators or such?
Yes: many operating systems can be run on simulators like qemu.
Can someone recommend a simplified roadmap to show how one would get sarted? I'm a little unsure where to even start.
Try to get a simple operating system which can be run on emulators, hack it and follow your curiosity. Don't be scared of messing with knotty code.
1) Most of the time for most and usually the lower end embedded system, you need to know C.
And I will still recommend you to get a vanilla development board to get yourself familiar with the work flow and tricky part of working with embedded system like debugging and cross compiling. You will run into trouble if you only rely on emulator.
You can try out The Linux Stamp, it is not expensive and is good for beginner but you do need some prior knowledge on Linux.
2) For high end embedded system, a good example is Smartphone from HTC (CPU speed can reach 1Ghz)or some other Android phone it run fast and you can even code Java on it.
C and the assembly specific to your chip.
No, you really need a real chip. Simulators aren't the real thing. You need to be able to deal with keypress jitter, voltage funkyness, etc.
The Arduino is the current fad for embedded hobbyists. I'm not a big fan of Harvard architecture, personally. But you will find oodles of help out there for it. I use an XCore for my thesis work and I have found it super easy to program multicore stuff. I would suggest starting with an AVR32 and going from there.
As everyone else is saying, you need to know C.
Have a look at AVR butterfly for a cheap development board.
Smileymicros have a simple kit with dev board and book:
http://www.smileymicros.com/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=41
The soon to ship Raspberry Pi board looks like an incredibly cheap way to get into this field.
Yup, Arduino would be the way to go. Agreed.. Cheap (about $20 to start) and has great API to get started with high level functions. C is a must though, can't avoid it. But if you can program in other languages you'll be all good.
My recommendation is to start shopping at http://www.sparkfun.com lots of examples to work from and helpful hints of what devices to buy.
I am working on a project, C programing language, to develop an application, that can be ported on to a number of different microcontroller platforms, such as ARM\Freescale\PIC microcontroller. I am developing this application on Linux now and then I will have to port it to the above said platforms.
I would like to know, are there any tools (open source preferably), using which I can determine the "code" and the data memory footprint\size, before porting it to the new platform.
I have been searching on "Google" for it and have not found anything so far, not even for Linux as well.
any help from you will greatly help me.
-Vikas
For a small program, much of the size is determined by the libraries/DLL your program depends on. Since you refer to ARM/Freescale/Pic I assume you're dealing with compact, embedded applications where data size is measured in bytes rather than MBytes.
For your own code, size differences will determined by:
word size (i.e. 32bit programs tend to be a bit larger /more data than 8 bit)
architecture (i.e. Intel code versus ARM, freescale, PIC)
In your case, I expect that PIC is the most critical part (for RAM/ROM constraints). So propably monitoring the PIC compile size during PC development is sufficient. The linker output will contain info on TEXT/DATA/BSS size, which you can monitor.
I generally work on embedded systems. In my work much of the data size is known at design time (i.e. number of buffers * buffer size). For code size, I have rules of thumb on different architectures which help me to do a sanity check at design time. For instance, I define a suite of some exising-code libraries, for which I know performance and size numbers for each architecture. This way I know what kind of ratio I can expect at design time. If the PC program has 1 MBytes of data, it won't fit in an 8-bit PIC.....
Nothing can tell you how much memory your application will need. You'll have to make some assumptions about how it will be used and try your application under different scenarios.
As you're testing, you can monitor the memory usage stats in the /proc file system or use the ps command to do the same.
The size of your text/code segment will depend on optimization level and back-end. GCC can be configured to generate that information for you.
Run-time is a little more difficult as Jeremy said. Besides his suggestion, you also might want to try gcov and/or gprof in order to analyse your program in the context of your most common use scenarios. This kind of instrumentation is focussed on complexity rather than size but at least you'll know better where to focus your memory analysis.
Your compiler can/will generate a map file. The map file will, generally speaking, have code and data size (or location ranges). There may be differences between different compilers for the different targets. And as pointed out in other posts here, your dependencies on supplied libraries will also impact overall memory usage.