Date: Fri, 30 May 1997 00:24:51 -0700 (MST) From: Don Yuniskis <dgy@rtd.com> To: narvi@haldjas.folklore.ee (Narvi) Cc: dgy@rtd.com, freebsd-hackers@freefall.FreeBSD.org Subject: Re: diskless hardware *design* suggestions Message-ID: <199705300724.AAA07362@seagull.rtd.com> In-Reply-To: <Pine.BSF.3.96.970524224929.12516A-100000@haldjas.folklore.ee> from "Narvi" at May 24, 97 11:06:35 pm
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It seems that Narvi said: > On Sat, 24 May 1997, Don Yuniskis wrote: > > > I suspect that a DMA channel of the SC400 could move enough bits. > > The problem would lie in the number of bcopy()'s, etc. needed to > > actually move the data to someplace useful... > > > > > But take a look at the SMC FEAST controller (91C100), it has > > > 32/16 bit bus support and is not meant specificly for PCI (actually, VL is > > > even mentioned). > > > > Yes, but the SC400 devices don't support *any* busmastering! > > So, that type of solution would necessitate the additon of > > a psuedo-dual-ported RAM just for the NIC. Kinda silly when > > there are gobs of DRAM sitting on the DRAM controller yet > > inaccessible to the NIC... > > Well, I am not sure if the FEAST chip even supports bus-mastering. It does > have support for 128K of external buffer RAM. Adding SRAM just for the NIC makes things bigger/more expensive... wasteful when there's gobs of DRAM sitting right there! > > > For 10 Mbit ethernet SMC also makes single-chip thingies > > > with direct ISA interface (91c94 - 91c96). They have 4.5KB RAM > > > on-board (dynamically allocated, in which upto 18 packets may be stored > > > at a time). There even seems to be enough information for writing a > > > driver. > > > > This is currently my best guess at a solution. However, I would > > have liked a faster device and I'm unsure of the overhead of > > moving bytes to/from it. > > It says on the DS it doesn't use any wait states on ISA, then again, it > seems to be a 16 bit wide IO device only (no memory mapping). My concern re: "overhead of moving bytes" was just that -- having to move the bytes from the "external RAM" into the main system DRAM. --don
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