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ARM THUMB mode Why and where?

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Zerox100

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Dear,

I have an study ARM mode. I interested in ARM THUMB mode. But is this mode is a useful mode? How many modern application really use this mode in recent application? What is the usage if this mode?

After reading some article on it, I got this assumption:
1- THUMB mode used in some application that there is limited memory resource. Am I right?
2- in ARMv8, Thumb mode is never used (cutted). Am I right?
3- THUMB mode makes CPU slow. Am I right?
4- in ARM mobile processor that there is large memory (32-256GByte) actually there is no need to THUMB mode. Am I right?


THX
 

Zerox100 said:
1- THUMB mode used in some application that there is limited memory resource. Am I right?
Click to expand...

It make sense once with this mode you can call instructions with 16 bits length in a core with 32-bits data bus. In other words, it is like being able to compress part of the instruction set originally made for 32 bits.

Zerox100 said:
3- THUMB mode makes CPU slow. Am I right?
Click to expand...

It is just the opposite, since the fetching for instructions takes more time to be accomplished than its execution; while program memory is located at external memories, part of the execution can be done internally (ALU, GPU, Registers, etc...). This way you spent less time in the process which is somehow the bootleneck of the process.
 

What about ARMv8? Does it support THUMB?
 

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