Got this kind of question too much, so I'll just go ahead and put it out here.
What is an embedded system?
Basically anything that is a computer running a system that performs a pre-determined function. Cell phone, printer, your car, your bank's ATM machine, your TV, DVD player, etc. Chances are, you have used one within the last 45 seconds (quote ARM)
How does an embedded system looks like?
It could look anything physically, but usually in terms of computer architecture it has a processor, RAM, ROM, and some I/O that it input from and output to. Once powered up, it receives "command" or inputs and process it for an output. Mostly likely, it is at least 1 chip running on an embedded CPU with integrated (internal) RAM, ROM, some custom logics, and IO to other chips.
In the software perspective, it usually runs a small program waiting for stuff to do, and sleep till the command/signal comes, then wake up, do the job, and goes back to sleep.
Think of running your car's engine control on a 12 year old computer on DOS, that's how embedded system looks like if it is not embedded. It wasn't that far fetch, your ECU most likely runs the motorolla 68k architecture that was once the brain of Macintosh.
How is embedded system different than your PC at home?
It is usually smaller (one chip or a few chips), less powerful (unless a high powered DSP unit for high performance application), cheaper, use less power, and are hidden from the user. It's usually design to do one task (or a few simple tasks) and do it just good enough. PC is usually overpowered because it can't anticipate what user will use it for. It is common to see 25Mhz CPU with 30KB RAM running simple task (flash memory card controller). Many system are also REAL TIME, meaning that it is guaranteed to respond to external command/signal within a deadline. PC usually will be ok if the program runs 1S or so, embedded system in many case are considered failure if it is late to finish its task (choppy video, mp3, etc).
What is ASIC?
It is the chip that contains everything needed to drive the system. Frequently it contains a CPU, RAM, ROM, some custom logic that perform tasks too slow for software, and the "secret sauce" that makes it expensive (i.e. decode cell phone signals or cancel the noises). The "chips" on your hard drive is one good example, it is custom build to handle everything in one unit, except the external RAM and NAND because it is cheaper to buy than to integrate those.
What is firmware?
The code that the ASIC runs, predetermined to do the task you need with the ASIC. Some are upgradable (flash memory based), some are not (ROM based). Usually come with the system that you buy and cannot be run else where (exception applied like the Linksys Routers that can run external firmware).
Why don't we just use a predefined hard circuits to perform the task, but instead have to put it on a processor with software/firmware? It seems too complicated.
True, but chips are now cheap and it is easy to make mistakes on complex logic. It is far more flexible to have an upgradable firmware that you can fix problem down the line. Imagine if you are 6 months behind the competitor, how much money you save on a 25-50 cents part if you are 6 months ahead and can sell $10 more for 20 million units? Also, chips need to sell in million units per month to reach economic of scale. Building a custom chip that you only need 20k unit per month is always more expensive than buying a programmable off the shelf chip that has a volume of 20 million a months.
Are there other ways to do embedded system other than ASIC with firmware?
FPGA is very powerful but way more expensive, usually reserved for high performance low volume units (like the high end CISCO routers that are sold for up to 1 million each, or some high end stereo systems that cost 3000 each). It would be suicidal to put a $30 chip on a $60 hard drive, you need to put something less than $4 on it.
Having a host computer running it will be even more flexible but bulky, and high power consumption. Many industrial systems like logic analyzer or medical instruments are run on PC with Windows XP (don't laugh). They are much easier to develop since you can just buy an off the shelf system instead of develop the hardware.
What is an embedded system?
Basically anything that is a computer running a system that performs a pre-determined function. Cell phone, printer, your car, your bank's ATM machine, your TV, DVD player, etc. Chances are, you have used one within the last 45 seconds (quote ARM)
How does an embedded system looks like?
It could look anything physically, but usually in terms of computer architecture it has a processor, RAM, ROM, and some I/O that it input from and output to. Once powered up, it receives "command" or inputs and process it for an output. Mostly likely, it is at least 1 chip running on an embedded CPU with integrated (internal) RAM, ROM, some custom logics, and IO to other chips.
In the software perspective, it usually runs a small program waiting for stuff to do, and sleep till the command/signal comes, then wake up, do the job, and goes back to sleep.
Think of running your car's engine control on a 12 year old computer on DOS, that's how embedded system looks like if it is not embedded. It wasn't that far fetch, your ECU most likely runs the motorolla 68k architecture that was once the brain of Macintosh.
How is embedded system different than your PC at home?
It is usually smaller (one chip or a few chips), less powerful (unless a high powered DSP unit for high performance application), cheaper, use less power, and are hidden from the user. It's usually design to do one task (or a few simple tasks) and do it just good enough. PC is usually overpowered because it can't anticipate what user will use it for. It is common to see 25Mhz CPU with 30KB RAM running simple task (flash memory card controller). Many system are also REAL TIME, meaning that it is guaranteed to respond to external command/signal within a deadline. PC usually will be ok if the program runs 1S or so, embedded system in many case are considered failure if it is late to finish its task (choppy video, mp3, etc).
What is ASIC?
It is the chip that contains everything needed to drive the system. Frequently it contains a CPU, RAM, ROM, some custom logic that perform tasks too slow for software, and the "secret sauce" that makes it expensive (i.e. decode cell phone signals or cancel the noises). The "chips" on your hard drive is one good example, it is custom build to handle everything in one unit, except the external RAM and NAND because it is cheaper to buy than to integrate those.
What is firmware?
The code that the ASIC runs, predetermined to do the task you need with the ASIC. Some are upgradable (flash memory based), some are not (ROM based). Usually come with the system that you buy and cannot be run else where (exception applied like the Linksys Routers that can run external firmware).
Why don't we just use a predefined hard circuits to perform the task, but instead have to put it on a processor with software/firmware? It seems too complicated.
True, but chips are now cheap and it is easy to make mistakes on complex logic. It is far more flexible to have an upgradable firmware that you can fix problem down the line. Imagine if you are 6 months behind the competitor, how much money you save on a 25-50 cents part if you are 6 months ahead and can sell $10 more for 20 million units? Also, chips need to sell in million units per month to reach economic of scale. Building a custom chip that you only need 20k unit per month is always more expensive than buying a programmable off the shelf chip that has a volume of 20 million a months.
Are there other ways to do embedded system other than ASIC with firmware?
FPGA is very powerful but way more expensive, usually reserved for high performance low volume units (like the high end CISCO routers that are sold for up to 1 million each, or some high end stereo systems that cost 3000 each). It would be suicidal to put a $30 chip on a $60 hard drive, you need to put something less than $4 on it.
Having a host computer running it will be even more flexible but bulky, and high power consumption. Many industrial systems like logic analyzer or medical instruments are run on PC with Windows XP (don't laugh). They are much easier to develop since you can just buy an off the shelf system instead of develop the hardware.
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