Re: Quiescing Nubus DMA?

[Donald Lee <MacBSD.68k%caution.icompute.com@localhost>]

It's hard to imagine any OS running reliably if it does not "take charge"
of such a peripheral card at boot time, to reset and initialize it.

How does MacOS do this?  I would think it would *have* to be done
in the ROM, since nothing else would be safe from the DMA engine.

I would expect that NuBus would have some sort of reset sequence, and
that would *have* to "park" the card.

No help, but curious. ;->

-dgl-

>All,
>
>given the size of the audience, this question should probably go to
>tech-kern, and may eventually. Still...
>
>I have (once again) taken up toying with an FWB Jackhammer Nubus SCSI card,
>which features a 53c720 controller. It looks like the 53c720 is active even
>after the kernel has taken over, punching random holes into memory early
>during the boot and way before Nubus is probed. I've looked at the sn(4)
>DMA code, but we have other means of learning early up that the
>corresponding DMA hardware is present, and silence it, so that does not
>really help.
>
>What is the general NetBSD take on this, short of hacking the booter into
>shutting down the 53c720 DMA before handing control to the kernel?
>Unfortunately, mac68k hardware does not go through a full reset sequence
>before booting into NetBSD.
>
>Puzzled,
>       hauke
>
>--
>"It's never straight up and down"     (DEVO)