ARM processor ARM7 vs. ARM9

Not much I believe, that would be more of a hardware rather than API change, The main change is in performance, the later core can go faster at the same clock and can be clocked higher.

I'd advise checking if the particular ARM9 you're getting it is an ARMv4 or ARMv5.

If you get an ARM9E for instance rather than ARM9TDMI you get the extras marked with a 5 or 5E in the § column in the ARM and Thumb-2 reference card.

http://infocenter.arm.com/help/topic/com.arm.doc.qrc0001m/QRC0001_UAL.pdf

You don't get Thumb-2 in ARMv5 but the interworking between ARM and Thumb is much better. Code compiled for the old way can be incompatible but I think this is the only problem you might find and it is worth the change.

Hi Faith,

You have it pretty much right. ARM7TDMI and ARM9TDMI (the core inside processors like the ARM920T) are architecturally identical (both architecture ARMv4T). The main differences are in the implementation so the ARM9T is a cached processor with a Harvard memory architecture and a 5-stage pipeline enabling a much highline clock speed and a lower CPI. The performance is therefore quite significantly higher. From a programming point of view, you won't notice much difference unless you need to access the system control and configuration features which will be a little more extensive on the ARM9T.

The ARM9E is architecture ARMv5TE and has some extra instructions for DSP algorithms and improved ARM/Thumb interworking.

To be honest both, even the ARM9, are fairly old technology these days and most developers are using Cortex cores these days. For high performance, application type programming, that would be cores like the Cortex-A9; for microcontrollers and deeply embedded applications, cores like Cortex-M3.

There are lots of resources here on the community which will help explain what's available the differences between the products.

Hope this helps.

Chris