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ARM9 replacing Cortex M3

Michael von Hauff
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    Note: This was originally posted on 8th January 2009 at http://forums.arm.com

    Hi,

    Thanks for the input everyone.

    Oops about using word to describe a halfword (16bit). The Cortex M3 is limited to 16bits for interfacing with the outside world (FMCS and GPIO ports are 16bit). So 16bits is my limit!

    There are definitely other issue to contend with (bus contention is one). But the reason I am so focused on the three things I mentioned (wake time, dma transfer speed, and power consumption) is because those three characteristics are the absolute deal breakers. If they are not met, the mcu in question is dropped without a second glance. Other issues that crop up will be dealt with later.

    However, since I am not an arm expert, I was hoping to gain some insight from other arm users!

    That is a good thing to know about the dma being a factor based on the vendor and not ARM. The GPIO pin issue was something else I was looking at, so thanks for the input on that too! The STM32 data sheet says you can drive the GPIOs (some ports) at 50MHz tops. That's fast enough for me!

    I am thinking that even a 133MHz bus would be fast enough if a DMA transfer take 4 bus cycles (Nyquist theorem, need >= 20MSamp/s pushed to DACs)


    So to direct the thread a little bit away from the DMA issue and more onto the wake time.

    Anyone have experience with ARM9 variants concerning wake time?

    The M3 was my first choice because it has a high speed internal oscilator, so you can be up and running at 8MHz (good enough for the first couple hundred instructions), and then switch over to the HS external.

    But now that I am looking at ARM9s I have to contend with no HSI. I was thinking that a specialized oscillator that has a fast start up time (they exist apparently) would help cut wake time, but what about the PLL? anyone know what the PLL lock time is on their ARM9 (ie, if you are using some arm9 variant, does your data sheet or experience tell you the pll lock time?)

    Thanks for all the input.

    Mike.
Reply
  • 0
    Note: This was originally posted on 8th January 2009 at http://forums.arm.com

    Hi,

    Thanks for the input everyone.

    Oops about using word to describe a halfword (16bit). The Cortex M3 is limited to 16bits for interfacing with the outside world (FMCS and GPIO ports are 16bit). So 16bits is my limit!

    There are definitely other issue to contend with (bus contention is one). But the reason I am so focused on the three things I mentioned (wake time, dma transfer speed, and power consumption) is because those three characteristics are the absolute deal breakers. If they are not met, the mcu in question is dropped without a second glance. Other issues that crop up will be dealt with later.

    However, since I am not an arm expert, I was hoping to gain some insight from other arm users!

    That is a good thing to know about the dma being a factor based on the vendor and not ARM. The GPIO pin issue was something else I was looking at, so thanks for the input on that too! The STM32 data sheet says you can drive the GPIOs (some ports) at 50MHz tops. That's fast enough for me!

    I am thinking that even a 133MHz bus would be fast enough if a DMA transfer take 4 bus cycles (Nyquist theorem, need >= 20MSamp/s pushed to DACs)


    So to direct the thread a little bit away from the DMA issue and more onto the wake time.

    Anyone have experience with ARM9 variants concerning wake time?

    The M3 was my first choice because it has a high speed internal oscilator, so you can be up and running at 8MHz (good enough for the first couple hundred instructions), and then switch over to the HS external.

    But now that I am looking at ARM9s I have to contend with no HSI. I was thinking that a specialized oscillator that has a fast start up time (they exist apparently) would help cut wake time, but what about the PLL? anyone know what the PLL lock time is on their ARM9 (ie, if you are using some arm9 variant, does your data sheet or experience tell you the pll lock time?)

    Thanks for all the input.

    Mike.
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