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Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing (Developers)

posted by RayeR , CZ, 08.01.2024, 18:38

Hi,
to get a real SB-compatible sound support under DOS (instead of half-working emulators) I designed and built my LPC2ISA adapter that allows me to connect any ISA card (including ISA DMA support) to relative "modern" motherboard via TPM header that exposes the LPC bus. There are some catches and hacks needed, whole story about the HW at VOGONS thread: https://www.vogons.org/viewtopic.php?p=1221763#p1221763

Currently it's working but with some minor SW issue - some programs that rely on soundcard autodetection doesn't find it properly. With manual settings it works. One example is Creative Sound Blaster Pro Test program from 1992 bundled with some SB drivers and also programs using MIDAS sound library that was very popular in '90 era and maybe more. The problem is caused probably by IRQ 7 sharing with LPT port but I cannot avoid this because of nature of PnP enumeration at boot. SETUP has no option to reserve IRQ for legacy device and when I disable LPT the IRQ is stolen by onboard PCI devices that don't work with IRQ sharing at all so I need keep LPT enabled at boot to other PCI devices keep out.

I tested SBPro test program on old 386 machine with native ISA without LPT and soundcard autodetection works fine there. On my MB with LPC2ISA bridge it ends with an error:
http://rayer.g6.cz/hardware/lpc2isa/sbptst1.jpg
http://rayer.g6.cz/hardware/lpc2isa/sbptst2.jpg
Programs using MIDAS doesn't detect soundcard too but when they can enable manual sound setup and I select IO, IRQ, DMA manually it works then.

I had some ideas to try, one was to completly disable the LPT block in SuperIO chip after boot. To do this a friend of mine Ruik made DOS ports of Linux tools ISADUMP and ISASET (maybe usefull for someone else):
http://rayer.g6.cz/download/download.htm#ISADUMP
When I disabled the LPT it helped with MIDAS programs so they autodetect soundcard properly then. But SBPro Test program still show an ERROR on IRQ7 and cannot continue (cannot force the value). I also tried to clear LPT address value and count in BDA but didn't helped. Any idea how SBPro Test perform IRQ autodetection and how to make in working? Any idea what else to clear/disable to kill any evidence of LPT that could disturb the SBPro Test?

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DOS gives me freedom to unlimited HW access.

Complete thread:

• Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing - RayeR, 08.01.2024, 18:38 (Developers)
  • Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing - DosWorld, 09.01.2024, 03:26
    • Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing - RayeR, 09.01.2024, 06:12
      • Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing - rr, 09.01.2024, 21:29
        • Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing - RayeR, 10.01.2024, 05:28
          • Sound Blaster Pro Test IRQ autodetect-how it wrks,IRQ sharing - RayeR, 14.01.2024, 06:27