28-03-2012, 01:11 PM
EMBEDDED SYSTEMS
Embedded System By David E. Simon ppt2.ppt (Size: 823 KB / Downloads: 68)
Examples of Embedded Systems
Telegraph
Allows a printer with only a high speed serial port to connect to a network
Looks like a little plastic box 2 to 3 inches by ½ inch thick
Has a pigtail connector for the serial connection and a network connector
What telegraph must do
On the network, data packets sometimes arrive out of order, data gets lost, and sometimes data arrives twice. Telegraph must make order out of chaos
Multiple computers on the network may want to print at once. Telegraph must allow one computer to print and somehow hold off the others.
Network printers must provide status info to any computer on the network that requires it, even if busy printing a job for some other computer.
Telegraph has to work with different types of printers.
Telegraph must respond rapidly to certain events, like various kinds of network frames.
Telegraph must keep track of time. If a computer which is sending a print job crashes, telegraph must be able to give up on that print job and print from another computer on the network.
Telegraph Development (cont)
Debugability – telegraph has no screen, no keyboard, no mouse, no speaker, no lights. When a bug occurs, it typically stops working…
Reliability – telegraph is not allowed to crash, which is typical of embedded systems. The sw must function without human intervention.
Memory Space – telegraph has limited memory, typically 32 kbytes of memory for its program and another 32 kbytes for its data.
Program Installation – we need special tools to install sw on these kinds of systems.
Cordless Bar Code Scanner
No problem with throughput…there just isn’t that much data
Power consumption – since the scanner is cordless, its battery is its only source of power. It is intended to be handheld, which limits its weight. How long must the battery last? An eight hour shift is probably the least we can tolerate.
Additional devices (cont)
A common way to handle the additional devices is to assign each of them a (contiguous) block of memory that is not used by the memory chips.
This scheme is known as memory mapping. The size that is needed depends upon what that chip’s needs are. The external device appears as just memory to the microprocessor and it is written to or read from by using standard C code memory access as shown on the next slide.
Hardware Considerations
Unlike software for which the engineering cost is virtually all of the cost, every copy of hardware costs money. Therefore, functionality is cheaper if it can be done in software.
Every additional part takes up space either in a chip or on a PC board.
Every additional part uses more power
Every additional part turns power into heat
Faster circuit components cost more, use more power, and generate more heat.
Embedded System By David E. Simon ppt2.ppt (Size: 823 KB / Downloads: 68)
Examples of Embedded Systems
Telegraph
Allows a printer with only a high speed serial port to connect to a network
Looks like a little plastic box 2 to 3 inches by ½ inch thick
Has a pigtail connector for the serial connection and a network connector
What telegraph must do
On the network, data packets sometimes arrive out of order, data gets lost, and sometimes data arrives twice. Telegraph must make order out of chaos
Multiple computers on the network may want to print at once. Telegraph must allow one computer to print and somehow hold off the others.
Network printers must provide status info to any computer on the network that requires it, even if busy printing a job for some other computer.
Telegraph has to work with different types of printers.
Telegraph must respond rapidly to certain events, like various kinds of network frames.
Telegraph must keep track of time. If a computer which is sending a print job crashes, telegraph must be able to give up on that print job and print from another computer on the network.
Telegraph Development (cont)
Debugability – telegraph has no screen, no keyboard, no mouse, no speaker, no lights. When a bug occurs, it typically stops working…
Reliability – telegraph is not allowed to crash, which is typical of embedded systems. The sw must function without human intervention.
Memory Space – telegraph has limited memory, typically 32 kbytes of memory for its program and another 32 kbytes for its data.
Program Installation – we need special tools to install sw on these kinds of systems.
Cordless Bar Code Scanner
No problem with throughput…there just isn’t that much data
Power consumption – since the scanner is cordless, its battery is its only source of power. It is intended to be handheld, which limits its weight. How long must the battery last? An eight hour shift is probably the least we can tolerate.
Additional devices (cont)
A common way to handle the additional devices is to assign each of them a (contiguous) block of memory that is not used by the memory chips.
This scheme is known as memory mapping. The size that is needed depends upon what that chip’s needs are. The external device appears as just memory to the microprocessor and it is written to or read from by using standard C code memory access as shown on the next slide.
Hardware Considerations
Unlike software for which the engineering cost is virtually all of the cost, every copy of hardware costs money. Therefore, functionality is cheaper if it can be done in software.
Every additional part takes up space either in a chip or on a PC board.
Every additional part uses more power
Every additional part turns power into heat
Faster circuit components cost more, use more power, and generate more heat.