Re: No cache on SiS471 VLB board

Posted on 2025-04-05, 05:31

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Sorry to necro this thread but wanted to thank you @LunarG for the information provided in this thread about the Iston S486G, particularly the pointer about JP30 and getting the AMD 5x86 running at the correct speed! I just added one of these boards to my collection and got it working perfectly …

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Re: Why is Amiga so popular with retro community ?

Posted on 2021-04-25, 12:48

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It's usually not about trying to compete with open standards. In Amigas case we'll give them the benefit of a doubt its becasue they couldn't just use open source hardware and the only solution was to build something from scratch. These days if you did these kinds of things you would be Apple and …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-25, 12:33

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Right. So I think I've finally tracked down all the signals I need. The INV* signal I need comes from the output portion of the I/O pin called W/R* (pin 104 on the 85C471) and is used together with EADS to invalidate a cache line. The CACHE* signal comes from pin 118 (PCD - Page Cache Disable). This …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-24, 21:29

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Nice! L1 WB may be a bit trickier, since it involves connecting several lines between the CPU and chipset, so that may require more than one jumper depending on how the motherboard was designed. This page is a good resource if you want to figure out the correct jumper(s) for L1 WB in a 5x86 among …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-24, 20:17

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Partial success! 😁 Got the multiplier working. Running Intel DX4 settings at the moment. As soon as I got the multiplier set, it reported as the correct CPU in POST, rather than 486DX4-Plus. So next goal is to get WB L1 cache. 😀

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Re: No cache on SiS471 VLB board

Posted on 2021-04-24, 19:20

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The board boots with Intel DX4 settings using my Am5x86, no problem, but Chkcpu claims that L1 cache is enabled in Write-Through mode. It's set to Write-Back in BIOS. The AMD and Intel DX4 / 5x86 processors do not support software-selectable L1 mode. The BIOS setting is only effective on Cyrix 486 …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-24, 15:23

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Right. I did a makeshift repair of my old test leads... I got impatient. I found that R17 on the CPU socket (where DX4 and Am5x86 are supposed to receive signal for CLKMUL) goes to JP30 pin 2 and JP32 pin 1. The board boots with Intel DX4 settings using my Am5x86, no problem, but Chkcpu claims that …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-24, 10:27

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I found a website with a table showing pin configs for different 486s. It shows lists "Intel DX4 (AMD 5x86)" in the same column, suggesting that I can just set my motherboard to P24C settings, and it should work perfectly with my 5x86. Also, since I'm getting 100MHz running the settings for "AMD DX- …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-23, 21:54

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

[ and try to figure out which jumpers specify model of CPU and which might indicate multiplier. You do not specify model by use of jumpers. You just set some signal to be routed here or there or use this voltage and set this pin in this state (high or low or floating) And the pin that indicate …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-23, 20:39

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It may be undocumented, if the board was released before the 5x86 (had this happen to me with a PCChips M921). If you feel like doing some detective work, you can use a multimeter to find a pin in the jumper header area that is connected to the CLKMUL pin of the CPU socket. If you find one, there …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-23, 14:59

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

5x86 support does not require any oscillator changes, that CPU runs at 33 MHz bus speed like most 486s. What you need is a jumper that sets DX4 internal multiplier to x2 instead of the default x3, as the 5x86 maps x2 to x4 internally to run at 133MHz. Other than that the settings should be the same …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-23, 09:37

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The POST string is as follows: (C) American Megatrends Inc., 40-PF02-001630-00101111-072594-SIS471G-F I also did a BIOS dump using NSSI, just because...

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Re: No cache on SiS471 VLB board

Posted on 2021-04-23, 08:45

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Never tried GETROM before, so I hope I did it correctly. Ran both the AT and XT executables just to be on the safe side.

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Re: No cache on SiS471 VLB board

Posted on 2021-04-23, 08:03

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The manual doesn't have any jumper settings for running 133MHz unfortunately. I can't read the label of the chip that is in the top right corner on the photo, nearest to the label OSC2. If we can find the datasheet on that, I'm guessing, it will provide some insight on the possible frequencies that …

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Re: Why is Amiga so popular with retro community ?

Posted on 2021-04-22, 20:24

by

by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

These days I find myself spending more and more time tinkering with my upgraded A500 (ACA500Plus 680CE00@21MHz, 1MB Chipmem, 8MB Fastmem, 8GB CF-IDE HDD, Plipbox Nano network adapter and HDMI-520 Upscaler/Flicker-Fixer) and I must say if I knew this kind of Amiga configuration was possible I may …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-22, 20:18

by

by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

One thing I'm wondering about is : what if the problem with cache was not L2 cache but L1 cache actually ? The 5x86 supports both Write-Through and Write-Back cache. But That DX2 might only support Write-Through ? Causing the board to fail to POST :) Thanks for the photo, we'll add this board soon. …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-22, 19:52

by

by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It's probably not properly configured to operate with a DX2 Can you please send a photo that is not 8bpp and also a picture of the POST string (or preferably a BIOS dump using this http://cd.textfiles.com/microhaus/mhblackbox3/MEMORY/GETROM.ZIP) so we can try to identify it and add this to UH19 ? …

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Re: No cache on SiS471 VLB board

Posted on 2021-04-22, 16:29

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by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The plot thickens. It occurred to me that I hadn't actually tried booting with the AMD 5x86 and a jumper in place on JP30 pins 1 and 2. So I did that now, and it's still got functioning cache. So who the heck knows why it's not working for the DX2 then. *shrug*

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Re: Why is Amiga so popular with retro community ?

Posted on 2021-04-22, 16:21

by

by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

These days I find myself spending more and more time tinkering with my upgraded A500 (ACA500Plus 680CE00@21MHz, 1MB Chipmem, 8MB Fastmem, 8GB CF-IDE HDD, Plipbox Nano network adapter and HDMI-520 Upscaler/Flicker-Fixer) and I must say if I knew this kind of Amiga configuration was possible I may …

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Re: Why is Amiga so popular with retro community ?

Posted on 2021-04-22, 16:16

by

by LunarG

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Having had an Amiga 1000 on release day, and an A500 sometime later in '87 I clearly recall the first and old days. I personally believe it was the amazing (at the time) custom chipset that was the downfall. So many things were baked into it. So many things not customizable and modifiable through …

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