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DataExpert EXp8449 - Intel DX2 66 Overdrive - Poor performance

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First post, by zuldan

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I managed to get a 486 motherboard running (https://theretroweb.com/motherboards/s/dataexpert-exp8449) however it's performance is really bad. I've done some benchmarks below and Doom is almost unplayable. I've set the BIOS settings to "Optimized" and made sure the turbo button jumpers are closed. Is there something silly I may not be doing?

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fyi, I stopped the test near the end by mistake, so that's why the graph is not complete.

Reply 1 of 8, by Babasha

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Did you try to set the turboto open position?

Need help? Begin with photo and model of your hardware 😉

Reply 2 of 8, by zuldan

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Babasha wrote on 2023-12-13, 01:33:

Did you try to set the turboto open position?

I'm pretty sure I did. I'll try again when I get home. I also haven't tried other memory, so I'll try that too.

Reply 3 of 8, by rmay635703

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It’s almost like the cache is disabled

Reply 4 of 8, by rasz_pl

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L2 Cache does maybe 10% difference, even disabling L1 wouldt slow 486 below 386 levels. This does look like Turbo throttling by the bios injecting wait states or SMM.

https://github.com/raszpl/FIC-486-GAC-2-Cache-Module for AT&T Globalyst
https://github.com/raszpl/386RC-16 memory board
https://github.com/raszpl/440BX Reference Design adapted to Kicad
https://github.com/raszpl/Zenith_ZBIOS MFM-300 Monitor

Reply 5 of 8, by MikeSG

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Which ever position the turbo switch is in, try the other setting (open/close)

Reply 6 of 8, by zuldan

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MikeSG wrote on 2023-12-13, 12:21:

Which ever position the turbo switch is in, try the other setting (open/close)

When I remove the jumper for turbo goes from 19mhz to 10mhz so turbo is 100 active.

Reply 7 of 8, by zuldan

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rmay635703 wrote on 2023-12-13, 02:54:

It’s almost like the cache is disabled

I think you're right. The strange thing is L1 and L2 cache are enabled in the BIOS but 2 programs below are reporting L1 is disabled

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I did notice that the motherboard doesn't know what CPU is installed. So maybe it doesn't know how to activate the cache?

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The motherboard is running firmware v1.4. Retroweb has version v2.3. I tried to upgrade the BIOS chip with my T48 programmer but the update failed. I plugged the BIOS chip back into the motherboard and it just started beeping. Motherboard is borked!

Anyway, I peeled off another sticker on the BIOS chip and to my horror it was a EPROM (UV) and not an EEPROM. I've ordered a EPROM UV eraser and a couple of new EPROM chips. Hopefully once I've erased the BIOS chip and flashed v2.3, the cache issue will be resolved.

Reply 8 of 8, by zuldan

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Just update to this issue. After updating the BIOS to v2.3, the motherboard now recognizes the CPU and the L1 cache is now active. I replaced the 486DX2-66 Overdrive with a 486DX4-100 Overdrive. The speed of the both CPUs massively increased!

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