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Thread: Questions about Make it 486 on a 386sx

  1. #21

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    TI486SXL(C) CPUs are somewhat notorious for not being able to double. I think it has something to do with the way TI implements the doubling feature, which unlike most other CPUs is disabled by default.
    Has anyone tried using the Cyrix DRx/SRx software to enable doubling? The CPU register used for doubling is used as the cache mapping register in the Cyrix branded chips.
    "Will the Highways on the internets become more few?"

    V'Ger XT

  2. #22
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    TI didn't implement anything, they were the fab for Cyrix and as part of the production agreement, TI was allowed to sell Cyrix designs under their own name. Both SGS Thompson and IBM were also fabs for Cyrix and had their own rebranded CPUs as well.

    All of the OEM branded parts were identical to Cyrix's chips, the only difference is that both TI and IBM tended to be more conservative with their speed grades. Cyrix was always playing catch up, especially into the mid 90s when they were far behind even AMD. They pushed their chips hard, which resulted in heat and power consumption issues that coupled with their weird FSB speeds, caused sometimes severe instability.

  3. #23

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    Your reply is well informed, but not correct. Time to read up on TI "potomac" CPUs.
    "Will the Highways on the internets become more few?"

    V'Ger XT

  4. #24
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  5. #25

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    These chips are Cyrix based, but apparently TI made unauthorised modifications, mainly increasing the cache size from 1kb to 8kb, and repurposing one of the CPU cache registers to enable/disable the clock doubling. The databooks for the Cyrix SLC/DLC and TI SXL/SXLC are available for free online if you really want to confirm the differences.

    http://bitsavers.informatik.uni-stut...ence_Guide.pdf
    http://bitsavers.informatik.uni-stut...heet_May92.pdf
    Last edited by Anonymous Coward; February 17th, 2019 at 07:45 AM.
    "Will the Highways on the internets become more few?"

    V'Ger XT

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