ravi@eneevax.UUCP (Ravi Kulkarni) (09/25/85)
The memory management unit on the ST is more of a memory controller. It handles refresh for up to 4 megs of memory organized as two banks. Even if you have different amounts of memory in the two banks it will configure it as one contiguous segment. The only memory management that it does that I know of is that certain areas of memory such as i/o space and and the first 1k of memory where the exception vectors are located are protected from writing when in user mode. Of course there could be undocumented features that we don't know about but then they could have easily made the text area of the operating system read only which I don't think is the case. >If this is the case, does that mean that the 512K in the machine is >really the CACHE for an external RAM disk? You may not be far off the mark. Rumors indicate that atari already has in prototype form an expansion box with a 32bit graphics processor. The ST might in this case be used as an i/o processor for the keyboard, disk, etc. Using the 512k as a cache would be very useful in speeding up the effective access times of todays slow hard disks. >I noticed that 1.33Mbytes/sec is about 10Mbit/sec, anybody know of an >Ethernet to SCSI interface? I know that this has been done. For example sequent has an ethernet controller off their scsi interface. I am very interested in this application. If somebody knows more about the atari interface and how it compares to SCSI please post it to net.micro.atari. >'Presenting...' describes the BIOS vectors and the BDOS vectors, where is >VDI? Is it a 'trap vector', a 'run-time library', or a 'link-time library'? The vdi or gsx calls are done via traps. I believe it uses trap#2. That is why you have to allocate those silly arrays when you use vdi calls since that is how you pass parameters. >Does VDI use the Graphics chip to do the painting, or does it 'bit bump' >like the MAC? The graphics processor is not documented very well(if at all) so the following is mere speculation. The graphics processor handles the generation of the video signals for both rgb and monochrome outputs. For monochrome output it uses a an internal crystal to generate the 70hz non-interlaced video. It also handles the 512 color palette for the rgb mode. The atari also has something called bit block transfer. There is a possibility that the graphics processor does this through a dma transfer. This is not an ordinary transfer since it involves non-contiguous sections of memory. A couple of things point to this. One try moving an open window on the desktop. You will notice that you cannot move it by single pixels in the horizontal direction but by small fixed increments implying word boundary limitations typical of dma operations. Also there are two screens one logical and one physical used for animation. Line drawing is done in software though. -- ARPA: eneevax!ravi@maryland UUCP: [seismo,allegra]!umcp-cs!eneevax!ravi
henry@utzoo.UUCP (Henry Spencer) (10/01/85)
> >I noticed that 1.33Mbytes/sec is about 10Mbit/sec, anybody know of an > >Ethernet to SCSI interface? > > I know that this has been done. For example sequent has an ethernet > controller off their scsi interface... Not so, sorry. The Ethernet controller and the SCSI interface are on the same board in the Sequent machines, but they are entirely independent. The Ethernet controller is not on the SCSI bus. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry