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QEMU and DOS (Ultra)-DMA drivers (Emulation)

posted by Japheth Homepage, Germany (South), 12.08.2022, 22:04

> So my question is: are there any DOS DMA drivers (UIDE, UDMA, XIDE, XHDD, .. ) that work with Qemu?
Yes, at least now; although it's a driver for Jemm only. I adjusted the xdma32 JLM contained in the Jemm package ( no binary available, just the source on github ).

As it has turned out, Qemu doesn't care about what DMA mode is set for a drive, it might be multi-word DMA 0-2 or Ultra DMA 0-6, there's no speed difference. DMA access is, however, significantly faster than PIO access ( which is the default ): on my VM, PIO access reads achieved about 9 MB/sec, while DMA access was 50 MB/sec up to 860 MB/sec ( the latter may occur if one reads a virtually "empty" qcow2 image ).

A warning: don't try (in qemu) the xdma32 binary supplied in the current release version (v5.82) - it might cause data losses.

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MS-DOS forever!

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