ARM7 Programming question!

writing ISR.

Do you mean ARM7 (e.g. ARM7TDMI) or ARMv7-M (e.g. a Cortex-M3)?

I ask because for something like a Cortex-M3 there are fewer instances where you _have_ to write in assembler.

It's arm7

There are a few examples then.  As Anandshastry suggested, exception handlers (at least the first level handler) are usually written in assembler.  Same goes for the vector table and initial reset handler.

We could add a few more examples to that list...

• Access to machine registers like the CPSR
• To use native machine instructions, like SIMD arithmetic, which do not map onto C syntax/semantics
• In relatively rare cases, to achieve higher performance than the compiler can achieve

Hope this helps

Chris

A few more:

When creating context switching code for an OS.

To ensure certain exact timing in some I/O or control operation (e.g. in certain hardware control code that you don't want any change of timing when switching between different compilers, even just a compiler version update). (Note: you can do this also by compiling the code into a library and then reuse it with different versions of compilers).

When you are an hacker and trying to .....(inject your favourite machine codes here )

When you are a student and your teacher (or exam questions) asked you to do so

thank u Mr.Joseph