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Cortex-M3 vs ARM7TDMI

Jayanth Acharya
Note: This was originally posted on 21st April 2011 at http://forums.arm.com

Trying to turn what was a simple hobby project based on Cortex-M3 with some serious enhancements/additions, into a semi-commercial product (might sell it at cost, or even opensource design/software), however I am at a crossroad of sorts, and need to decide whether I could stick to Cortex-M3 or move to ARM7TDMI, since those seem to be comparably priced, although from max DMIPS standpoint, are much lower than those on latest Cortex-M3s. My query is, how much of a factor is DMIPS in my circumstance.

Given some very rough (& not very scientific) estimates, I'd require around 120DMIPS of performance which I might be able to squeeze into say 80DMIPS if I go with commercial libraries & invest significantly (time/effort) in optimizing, which given the nature of the project (desire to sell at-cost or opensource) will be difficult, if not impossible. The point where I do hit the limits of Cortex-M3 is the onboard SRAM. This is where I am in some confusion, as to whether I should try a switch to ARM7TDMI ? Will the Cortex-M3's with External-Memory support, help address my issue ?

~Jay
Parents
  • Note: This was originally posted on 22nd April 2011 at http://forums.arm.com

    From my experience if the initial project estimation shows 120DMIPS two scenarios are very likely:

    1) You manage to squeeze the requirement down to say 80DMIPS

    2)  Soon you have add new features that require twice the initial performance.

    And there are two approaches:

    1) Start with a hardware platform that is at least twice as powerful as you think you may need. With other words take a look now at  ARM9, Cortex R4 or A8 ;-)

    2) Invest a little bit more time in the software side. Make it hardware independent. If you use RTOS then probably you have already some HAL.

    Personally, I prefer the second approach.  Well structured software with good HAL can be ported easily for different platforms, so you can try many and use the best.  But more importantly you can always add new featurrs.







Reply
  • Note: This was originally posted on 22nd April 2011 at http://forums.arm.com

    From my experience if the initial project estimation shows 120DMIPS two scenarios are very likely:

    1) You manage to squeeze the requirement down to say 80DMIPS

    2)  Soon you have add new features that require twice the initial performance.

    And there are two approaches:

    1) Start with a hardware platform that is at least twice as powerful as you think you may need. With other words take a look now at  ARM9, Cortex R4 or A8 ;-)

    2) Invest a little bit more time in the software side. Make it hardware independent. If you use RTOS then probably you have already some HAL.

    Personally, I prefer the second approach.  Well structured software with good HAL can be ported easily for different platforms, so you can try many and use the best.  But more importantly you can always add new featurrs.







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