lauren@vortex.COM (Lauren Weinstein) (10/24/90)
Here are a few SCSI questions of my own for the collected wisdom: 1) What is "synchronous negotiation" mode? Does this refer to negotiating whether or not synchronous transfers will be done? By default, I assume the AHA-1540B does synchronous transfers, even with the "synchronous negotiation" mode disabled? (As it is by default on the 1540B.) 2) Is the 5.0 default DMA transfer rate for the 1540B correct for most situations? 3) How many disks with embedded SCSI controllers will the 1540B support? The 1540B documentation says that SCSI disks should be set to to ID 0 and 1. Why not ID 2 and 3 as well? Is the limit 2 or 4? Thanks much. --Lauren--
dwc@olivey.olivetti.com (Dan Crocker) (10/26/90)
In article <62.UUL1.3#1@vortex.COM>, lauren@vortex.COM (Lauren Weinstein) writes: > Here are a few SCSI questions of my own for the collected wisdom: > > 1) What is "synchronous negotiation" mode? Does this refer to negotiating > whether or not synchronous transfers will be done? By default, I > assume the AHA-1540B does synchronous transfers, even with the > "synchronous negotiation" mode disabled? (As it is by default on the > 1540B.) Synchonous negotiation is the message passing sequence for two devices to agree on the rate at which synchronous xfers can take place. Basically, one side might say: "I can do 5 MB/SEC" and the other might answer: "I can do 3 MB/SEC". The final rate will always be the lower of the two. As for the adaptec HA, I seem to remember that, if synchonous xfers are disabled, it will respond to a synchronous negotiation but it will not initiate it. All the devices that I've seen (mostly disks) will use asynchronous mode unless the initiator asks for synchronous mode (even if it can support sync mode). If you have a device that can do sync xfers, I think you need to enable them on the HA. > 2) Is the 5.0 default DMA transfer rate for the 1540B correct for > most situations? This should be fine since, if you connect a device that can't go that fast, it will tell the HA and transfers will take place at the lower rate. > > 3) How many disks with embedded SCSI controllers will the 1540B support? > The 1540B documentation says that SCSI disks should be set to to > ID 0 and 1. Why not ID 2 and 3 as well? Is the limit 2 or 4? The ID settings are for accessing the disks using standard INT13 calls (drive 80 = ID 0, and drive 81 = ID 1). If you set the ID's to anything else, DOS will not recognize them. If, however, you have a DOS device driver or you are using another operating system with the right driver, you should be able to connect the SCSI maximum of 7. One comment about sync. xfers. I have seen drives whose async and sync transfer rates are the same (i.e. 3 MB/SEC). The only point here is that you don't necessarily gain anything by using sync xfers. Consult your drive docs to find out for sure. Hope this helps... dan
bote@csense.uucp (John Boteler) (10/27/90)
dwc@olivey.olivetti.com (Dan Crocker) claimed: >In article <62.UUL1.3#1@vortex.COM>, lauren@vortex.COM (Lauren Weinstein) writes: >> Here are a few SCSI questions of my own for the collected wisdom: >> 1) What is "synchronous negotiation" mode? Does this refer to negotiating >> whether or not synchronous transfers will be done? > >it can support sync mode). If you have a device that can do sync xfers, >I think you need to enable them on the HA. >> 2) Is the 5.0 default DMA transfer rate for the 1540B correct for >> most situations? > >This should be fine since, if you connect a device that can't go that fast, >it will tell the HA and transfers will take place at the lower rate. I think the question referred to the DMA xfer rate to memory, not across the SCSI bus itself. Read on... Here it is from the horse's mouth: >From: neese@adaptex.UUCP Newsgroups: comp.unix.sysv386 Date: 10 Sep 90 16:13:00 GMT The bus speed has nothing to do with the DMA rate. It's more important to consider the memory bus rate, which is not driven by the bus clock speed. As the card is a bus master, it does ignore the bus clock speed and uses the programmed DMA rate to do all data transfers. The only signal that can affect the actual transfer rate is the IOCHRDY signal. The DMA speed is completely independent of the BUSON time. If anything, you would want to set the DMA speed as high as the machine will take it. I always recommend 6.7MBytes/sec for the DMA speed as this is much faster than the SCSI bus can run and will help to minimize any disconnects that may occur due to the adapter starving the device buffer it is connected to. [ editor's note: I had problems on a 'G2' 286 motherboard at 6.7; I had to switch to 5.7MB/sec for reliable performance. ] >>I've installed the Sync option jumper on the controller. >that jumper doesn't matter - it's setting is overridden by ISC's scsi >driver. Software cannot override this jumper. This jumper simply indicates who will attempt to negotiate for synchronous protocol. If the jumper is installed the AHA-154x board will negotiate for it, if the jumper is removed the adapter expects the device to negotiate for it. I would allow a device to do the negotiation as some devices will do the negotiation on each data transfer. If the 154x does the negotiation, it will only be done once. >>With BUSON 5, BUSOFF 9 and DMASPEED 0; the system seems to be >>performing just fine. > >sure, these are the 'works 100%' parameters. not the 'works 100% and >performs 100%' paramters. The system will perform with these paramters, but not they are not the optimum values. It actually takes some experimentation to find what is best for any given environment. The variables that come into play are the device(s) connected, the size of any given data request, and the actual speed at which data can be transfered across the AT bus. Roy Neese Adaptec Senior SCSI Applications Engineer UUCP @ uunet!swbatl! {nominil,merch,cpe,mlite}!adaptex!neese -- John Boteler bote@csense {uunet | ka3ovk}!media!csense!bote SkinnyDipper's Hotline: 703 241 BARE | VOICE only, Touch-Tone(TM) signalling
ts@cup.portal.com (Tim W Smith) (10/30/90)
<Synchonous negotiation is the message passing sequence for two devices <to agree on the rate at which synchronous xfers can take place. Basically, <one side might say: "I can do 5 MB/SEC" and the other might answer: <"I can do 3 MB/SEC". The final rate will always be the lower of the two. Actually, it might have to go a few rounds before it gets resolved. Some devices only implement a subset of the possible synchronous periods and offsets. For example, supposed the first device in the above example can do 2, 4, and 5 MB/SEC. When it gets the response "3 MB/SEC" from the second device, it will have to let the other device know that it has not accepted this, and then try to negotiate 2 MB/SEC. If you are writing host software, be careful. Many devices screw up message handling. For example, I have a case where the Sony 40 meg drive that Apple sells blatently violates the SCSI protocol during message handling. I don't remember the exact details, but basically the drive gets confused, asks the host for a message when the host doesn't have one, so the host sends a NOP, and the drive then just disconnects from the bus! This case can show up during synchronous negotiation with this drive. This is very annoying! Tim Smith