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Atmel ARM AT91RM9200 SDRAM Issue

Discussion in 'Embedded' started by Jack Klein, Nov 9, 2004.

  1. Jack Klein

    Jack Klein Guest

    It appears that the SDRAM controller built into Atmel's AT91RM9200 ARM
    9 chip only supports a burst length of 1.

    Exactly what use is an SDRAM burst with a length of 1? What advantage
    does it have over an ordinary (non-burst) SDRAM access?

    Ulf, are you there?

    Jack Klein
    Home: http://JK-Technology.Com
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    Jack Klein, Nov 9, 2004
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  2. It appears that the SDRAM controller built into Atmel's AT91RM9200 ARM

    Do you mean that it does one asynchronous cycle and the only read one
    additional word in the burst?
    The burst length is not configurable by the user, for sure.
    Did not check in the oscilloscope (dont have one) but the burst length
    should be
    dependent on the bus master inside the chip.
    The PDC does not use burst, and I think there should be FIFOs in the PDC.

    One would think that you would burst at least one cache line,
    but comments from the at91 support team indicates however that you are
    Ulf Samuelsson, Nov 11, 2004
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  3. "Ulf Samuelsson" ...


    I've used other ARM-cored chips (NetSilicon Net+ARM) that specified a "one
    cycle write burst".

    When asked, the supplier explained that, after the burst transfer mode is
    entered, on each write cycle WITHIN THE SAME PAGE the lower bits of the
    address are supplied by the CPU (much like the good old 'page mode DRAM').
    Thus, it kept doing "single cycle" accesses as long as the transfer was
    within the same page.
    That explanation, with some study, fits the description in the SDRAM

    Maybe this is the same with the Atmel?

    Arie de Muynck
    Arie de Muynck, Nov 12, 2004
  4. Everyone is limited by whatever ARM has decided, and if their core does
    not generate burst requests, then is it hard for the bus interface to
    implement it.
    Did not read that part of the ARM920T datasheet.
    I think the burst is more important on read though.
    Ulf Samuelsson, Nov 12, 2004
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