Subject: Re: SCSI questions
To: Greg Cronau <>
From: Michael L. VanLoon -- Iowa State University <>
List: current-users
Date: 05/14/1994 01:02:10
>>>I am currently running Netbsd current from the Aprill 6th sources.
>>>My machine is as follows:
>>>	AMI Enterprise III EISA 486-66 with 12meg.
>>>	Bustek 747S EISA Fast-SCSI at 0x330, int-11, DMA-5
>>>	Adaptec 1542B ISA SCSI at 0x334, int-12, DMA-6
>>>2 days ago I opened the machine up to make 2 addtions: I added an additional
>>>8 meg of memory to bring the total to 20megs,
>>>5.) Does Netbsd properly handle DMA to ISA devices from memory beyond the
>>>    16mem boundary?

>>No.  It has been posted repeatedly that it doesn't.  The ISA bus
>>doesn't address more than 16 meg, and NetBSD doesn't yet do anything
>>to compensate for that.  Your EISA BusLogic card should work fine in
>>20 meg, but the ISA-bus Adaptec will only work if you have less than
>>16 meg.

>Ok, thanks. I must have missed the earlier posts. I knew that an ISA
>bus master card couldn't get to memory beyond 16meg directly, but most PC
>based UNIX that I have used, have included some buffer dancing logic to 
>make sure the DMA is always below the 16meg boundary. I just didn't know
>whether netbsd was capable of this.

Well, the stubs are there, the code has just never been written to do
the actual dance.  There is a performance hit for doing it this way,
however, since you're doing a lot more copying for each disk transfer.
An EISA board will just plain be faster in this scenario.

I know it isn't a high priority -- any idea on when bounce buffers
might make the list?


 Michael L. VanLoon                 Iowa State University Computation Center                    Project Vincent Systems Staff
  Free your mind and your machine -- NetBSD free Un*x for PC/Mac/Amiga/etc.