Re: Linux x uClinux for ColdFires: what is the best for what?

> David Brown wrote:
>> With higher frequency and higher performance devices, you have to take
>> more care with your memories and buses, and you have more worries about
>> your power supplies and decoupling.  You often need more voltage levels
>> (the v4 has 1.5V for the core, 1.8/2.5V for the memory buses, and 3.3V
>> for IO - the 5234 with which I am most familiar has 1.5V core and
>> everything else at 3.3V).  It is typically easier on slower devices to
>> attach other peripherals to the external buses without glue logic, level
>> converters, etc.
>
> Well, therein lies the rub.  As soon as you start supporting DDR of any
> kind, you get away from being able to produce a device with only two
> voltage rails.  The MCF523x family only supports SDR, so it never had a
> reason to support other than just I/O and VDD supplies.
>
> The MCF5445x still maintains a 3.3V general-purpose memory bus (FlexBus)
> for connecting up everything else but your SDRAM.  In the future, I'm
> looking to move the FlexBus to its own dedicated supply rail in order to
> support flashes and FPGAs/CPLDs with 1.8V I/Os as a means of reducing I/O
> power.  This would up the number of supply rails to four (core, SDRAM,
> FlexBus, and digital I/O), but you could still run the FlexBus at 3.3V, if
> desired.
>
>> I haven't used any v4 cores, so my rough comments are only based on my
>> reading of datasheets and application notes.  But our move from the
>> older, slower MC68832 to the MCF5234 required a bit step in board
>> complexity and quality - I would plan for another step up, though perhaps
>> not as large, in doing a v4 board.
>
> I think we've made the MCF5445x family quite friendly for board design,
> especially on the 256-ball MAPBGA variants.  We're trying to take the
> lessons we've learned from doing the package and substrate design for
> those devices and apply them to new higher end parts going forward.
>
>> I you want to tell me that I'm wrong, and that the MCF5445x is as easy to
>> use as the MCF5234 (baring the lack of a TPU), then go ahead - I'll
>> listen!  I like the ColdFire architecture, and if the v4 will give me a
>> lot more processing power for little more complexity, then it's
>> definitely good to know.
>
> I think I mentioned it before, but I am hardly an expert on board design,
> so I could be wrong on all counts :-(  That said, I had plenty of help
> from some real experts on the MCF5445x, so I think we've made that family
> one of our better examples of how to pin out and package a device.  Of
> course, by saying as much, I'm now setting myself up for pot shots from
> the peanut gallery, so let the shooting commence :-)
>
> John Bodnar
> Systems Engineer
> Microcontroller Solutions Group
> Freescale Semiconductor, Inc.
>
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