Subject: Re: ISA bus-master DMA on arc
To: None <>
From: M. Warner Losh <>
List: port-arc
Date: 07/18/2006 01:37:48
[[ sorry for the long lag in my reply ]]

In message: <>
            Izumi Tsutsui <> writes:
: wrote:
: > I've had a buslogic ISA controller work in my Deskstation ARCstation
: > (aka rPC44) under OpenBSD/arc.  It was a special hacked up driver that
: > pefo wrote to make it work...
: Hmm, thanks for your info. It looks rPC44 uses physical address
: for DMA address of ISA bus-master devices.
: (i.e. lower 24bit of KSEG1 address)

This makes a certain amount of sense, because the ISA bus can only
reference 16MB (lower 24bit) via busmaster/dma.

The rPC44 is as close as you can get to a 486 machine with a MIPS
R4400PC bolted in place of the 486.  The cache memory is slow (which
is horrible for MIPS performance), and it has nearly all of the warts
of the x86 of the era, plus a few more of its own.

: On the other hand, NEC PCI based machines (my NEC-JC94 etc.)
: use JAZZ DMA TLB for DMA address of PCI bus-master devices.
: I wonder what DMA address should be used for EISA based
: NEC or PICA machines (which have JAZZ-ISA bridge)...

I believe that PICA machines have a different set of constraints on
DMA addresses than the rPC44 does.  But I may be getting the PICA
based machines confused with the Deskstation Tyne machines which I
know had a special fast SRAM for DMA.