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Re: Linux x uClinux for ColdFires: what is the best for what?
by David Brown-4
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John Bodnar wrote:
>
> David,
>
> I'm curious about this statement:
>
> David Brown wrote:
>> As for the V2 versus the V4 - you get more processing power for your
>> money with a V4, but more microcontroller-style peripherals with most
>> V2 devices, and a V2 board is going to be easier and cheaper to make.
>> But that depends on the sort of boards you are used to making.
>
> What do you consider more MCUish that we've put on a V2 versus what
> we've put on a V4. If you look at a part like the MCF5270 or MCF5208
> and the MCF54450, they are similar apart from the cores.
>
> If you're thinking about single-chip flash devices, I agree, that the
> differences are greater. We generally don't put ADCs on devices that
> run from SDRAM, because we usually can't afford the pins and customers'
> ADC requirements tend to vary widely. Of course, if enough people ask,
> that is something that can change.
>
> For systems that run from SDRAM, especially the double data rate
> varieties, I'm not sure there's a huge world of difference between the
> board design for something like the MCF5208 and for the MCF54450.
>
> Both support DDR1 and mobile DDR (LPDDR) SDRAM. The MCF5208 has
> dedicated DQ, DQS, and DM lines for the DDR while the address bus is
> shares among all memories. The MCF54450 has a completely dedicated DDR
> bus, so I tend to think that board layout is of similar complexity for
> both. Of course, the DDR clock on the MCF5208 tops out at 83.33 MHz
> (well, if you're not overclocking :-) vs. 120 (or is it 133) MHz for the
> MCF54450, so a little more attention to high frequency stuff is
> necessary for the latter.
>
> Best regards,
>
> John Bodnar
> Systems Engineer
> Microcontroller Solutions Group
> Freescale Semiconductor, Inc.
>
Certainly the V2 microcontrollers with flash and other peripherals
built-in are a different matter, and ADCs are not something you
generally want in a high performance processor anyway.
I was making a more general hand-waving comment about the complexities
of boards with higher performance processors. Perhaps it's a bit
unreasonable to talk about microcontroller-style peripherals (although
I'm used to the MCF5234, with a TPU - you don't have v4 cores with a
TPU, do you?). But I still think board complexity is relevant.
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.
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 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.
mvh.,
David
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>
> David,
>
> I'm curious about this statement:
>
> David Brown wrote:
>> As for the V2 versus the V4 - you get more processing power for your
>> money with a V4, but more microcontroller-style peripherals with most
>> V2 devices, and a V2 board is going to be easier and cheaper to make.
>> But that depends on the sort of boards you are used to making.
>
> What do you consider more MCUish that we've put on a V2 versus what
> we've put on a V4. If you look at a part like the MCF5270 or MCF5208
> and the MCF54450, they are similar apart from the cores.
>
> If you're thinking about single-chip flash devices, I agree, that the
> differences are greater. We generally don't put ADCs on devices that
> run from SDRAM, because we usually can't afford the pins and customers'
> ADC requirements tend to vary widely. Of course, if enough people ask,
> that is something that can change.
>
> For systems that run from SDRAM, especially the double data rate
> varieties, I'm not sure there's a huge world of difference between the
> board design for something like the MCF5208 and for the MCF54450.
>
> Both support DDR1 and mobile DDR (LPDDR) SDRAM. The MCF5208 has
> dedicated DQ, DQS, and DM lines for the DDR while the address bus is
> shares among all memories. The MCF54450 has a completely dedicated DDR
> bus, so I tend to think that board layout is of similar complexity for
> both. Of course, the DDR clock on the MCF5208 tops out at 83.33 MHz
> (well, if you're not overclocking :-) vs. 120 (or is it 133) MHz for the
> MCF54450, so a little more attention to high frequency stuff is
> necessary for the latter.
>
> Best regards,
>
> John Bodnar
> Systems Engineer
> Microcontroller Solutions Group
> Freescale Semiconductor, Inc.
>
Certainly the V2 microcontrollers with flash and other peripherals
built-in are a different matter, and ADCs are not something you
generally want in a high performance processor anyway.
I was making a more general hand-waving comment about the complexities
of boards with higher performance processors. Perhaps it's a bit
unreasonable to talk about microcontroller-style peripherals (although
I'm used to the MCF5234, with a TPU - you don't have v4 cores with a
TPU, do you?). But I still think board complexity is relevant.
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.
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 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.
mvh.,
David
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