Working of IN CIRCUIT EMULATORS(ICE)-help me understand it plz...

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Dear all,
   My understanding of ICE are that they are typically CPU emulators,I
mean that when you want to hook or spy into the CPU bus cycles and
inspect whats happening in the bus level,ICEs are used.AFAIK,ICEs  are
hardwares which contain a processor for the real target board you are
going to emulate with.Basically it contains a pod and a bus which will
help me to connect my ICE to real target.So as far as the connection is
concerned,I will replace the cpu of the target board with ICE's CPU.So
ICE has a inbuilt software which will show me up whats going on in bus
So My understanding is target hardware's CPU is getting replaced with
First of all I would like to know whether my understanding is correct
regarding ICE and its connections?

Some of my colleagues are saying that,ICE's dont typically completely
replace the target processor,as I have understood ,rather it will be
working in Master/Slave mode where ICE's processor will be master and
my target processor will be slave,and in effect the master ICE will
control whats going on in the slave.

Are my colleagues correct or me?

I would like to learn more about ICE's.Any help will be great doing.
Can anyone explain me this or else point me to a good links which will
help me to understand working of ICE's in embedded projects...

Looking farward for all your replys and advanced thanks for the same,

Re: Working of IN CIRCUIT EMULATORS(ICE)-help me understand it plz...

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The ICE's that I have used (68HC11 & H8/530) have (IIRC) had CPU emulators
on the board. This is typically going to be required so that you can inspect
register values and also inspect/change memory locations without upsetting
the state of the 'processor' whilst it is between instructions. You also
need to be able to halt internal timers etc whilst debugging.

Also, some processors don't like being halted (having their clocks stopped).

Having said that, I can imagine some processor architectures would lend
themselves to being used in an ICE without requiring a CPU emulator.
Motorola Coldfire, for example, supports 'hardware' debugging in-circuit via
its BDM interface. I'm sure others offer similar capabilities that would
lend themselves to some sort of ICE arrangment.

So, you're probably both right!


|              Mark McDougall                | "Electrical Engineers do it
|  < |   with less resistance!"

Re: Working of IN CIRCUIT EMULATORS(ICE)-help me understand it plz...
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Typically a classic ICE has its own CPU onboard, and that replaces the
emulated CPU. Most of the lines from the emulation CPU are fed directly
into the board under test, with a few signal lines such as read and write
processed so that the ICE CPU can perform reads and writes to local
memories on the ICE itself. This is used both to simulate target memory,
allow the CPU to do things like load a program into target memory, read
internal registers, etc.

A lot of ICEs require that the CPU on the target be vacant, and probally
replaced with a special pin socket or similar. The ICEs that allow the
CPU to remain in system are activating a signal pin on the board's CPU
that tells it to disable itself.

Other solutions, like JTAG, that call themselves ICEs, are not really
ICEs, they are just using the name.

ICEs in general fell out of favor, because their increased pin capacitence
and timing problems cause the emulated system to be less stable. JTAG
style solutions work much better.

Re: Working of IN CIRCUIT EMULATORS(ICE)-help me understand it plz...

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It depends.  What CPU?
first ICE do not let you inspect the bus. That would be a logic analyzer.
It allows you to pause the CPU and look at registers and memory.  Some
replace the CPU with a bondout.  Others disable the CPU on board and use
the PODs CPU.  Other connect to the CPU via a special serial port on the
chip. (usually JTAG)
Never bit bang without one.

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