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Xscale PXA255 versus PXA250

Discussion in 'Embedded' started by Guest, Aug 27, 2003.

  1. Guest

    Guest Guest

    Hi.

    I was considering either Intel's Xscale PXA255 and Motorola's
    Dragonball MX1 for a new design based on Linux/RTAI. As Dragonball's
    LCD controller doesn't support double panel STN LCDs I decided to go
    with Xscale. Besides, Linux support seems to be more mature for Xscale
    than for Dragonball. I have a question though: the aforementioned
    support seems to be for PXA250. From data sheets and other sources of
    information, I learned PXA255 is mostly compatible with PXA250, with
    several bugs fixes and newer silicon technology. So, am I right to
    assume that I won't have much trouble running Linux on PXA255?

    TIA.

    Elder.
     
    Guest, Aug 27, 2003
    #1
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  2. Guest

    Tim Clacy Guest

    I can't tell you whether you'll have any trouble with Linux on PXA255, but I
    think I'm right in saying that PXA210/250 are discontinued in any case.
    PXA255 has all of the fixes that accumulated up to stepping C0 of PXA250,
    but there are still 'errata'.
     
    Tim Clacy, Aug 27, 2003
    #2
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  3. David Turvene, Aug 30, 2003
    #3
  4. Guest

    Tim Clacy Guest

    Hmm, that sounds good if you read it fast. In actual fact, the PXA255 has
    one clock configuration that has a slightly faster internal bus clock than
    the original PXA210/250... but the flip side is that only a fraction of the
    original PXA210/250 range of clock configurations are left as valid and
    working.
     
    Tim Clacy, Sep 1, 2003
    #4
  5. On 27 Aug 2003 06:12:02 -0700 (Mad@Spammers) wrote:

    Do not use pxa250! It has LOOOOOTS of hw bugs!
    I haven't seen the fixed version (pxa255) but pxa250 on 400MHz is slower
    than the 206MHz StrongARM 1110.
    Best Regards,
    --
    Alexander Popov ProSyst Bulgaria Inc.
    RTOS Leader 48 Vladajska Str.
    RTOS and JVM Sofia 1606, Bulgaria
    Phone: +359 2 952 35 81/203 http://www.prosyst.com
    Mobile: +359 87 663 193 OSGi Technology Leaders
     
    Alexander Popov, Sep 1, 2003
    #5
  6. Guest

    Tim Clacy Guest

    PXA255 is not a fixed version of PXA250; a lot of the errata remain but have
    been converted to documentation and/or specification changes. It's true that
    some errata are fixed; those that accumulated up to stepping C0 of PXA250.

    Despite much PXAxxx-induced hairloss, I have to defend the speed issue.
    XScale at 400MHz is almost 2 x faster than StrongARM at 206MHz.... but only
    for register operations (internal). The fact that you don't see any benefit
    from this speed demonstrates the folly of equating MHz with application
    performance under an OS; you can still brew a pot cup of coffee in the time
    it takes for Windows XP to get it's act together after power up... despite a
    few GHz.

    MHz mean nothing unless you have a single-register intensive thread of
    execution; An OSs running on a 400MHz CPU will waste four times as much time
    context switching than on a 100Hz CPU. Just about every thing that the
    microprocessor architects do to speed up execution of instruction sequences
    makes context swithing more expensive. The same is true of compiler writers.
     
    Tim Clacy, Sep 1, 2003
    #6
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