Announcement

Collapse

Forum etiquette

Our mission ...

This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

This forum has been around in this format for over 15 years. These rules and guidelines help us maintain a healthy and active community, and we moderate the forum to keep things on track. Please familiarize yourself with these rules and guidelines.


Remain civil and respectful

There are several hundred people who actively participate here. People come from all different backgrounds and will have different ways of seeing things. You will not agree with everything you read here. Back-and-forth discussions are fine but do not cross the line into rude or disrespectful behavior.

Conduct yourself as you would at any other place where people come together in person to discuss their hobby. If you wouldn't say something to somebody in person, then you probably should not be writing it here.

This should be obvious but, just in case: profanity, threats, slurs against any group (sexual, racial, gender, etc.) will not be tolerated.


Stay close to the original topic being discussed
  • If you are starting a new thread choose a reasonable sub-forum to start your thread. (If you choose incorrectly don't worry, we can fix that.)
  • If you are responding to a thread, stay on topic - the original poster was trying to achieve something. You can always start a new thread instead of potentially "hijacking" an existing thread.



Contribute something meaningful

To put things in engineering terms, we value a high signal to noise ratio. Coming here should not be a waste of time.
  • This is not a chat room. If you are taking less than 30 seconds to make a post then you are probably doing something wrong. A post should be on topic, clear, and contribute something meaningful to the discussion. If people read your posts and feel that their time as been wasted, they will stop reading your posts. Worse yet, they will stop visiting and we'll lose their experience and contributions.
  • Do not bump threads.
  • Do not "necro-post" unless you are following up to a specific person on a specific thread. And even then, that person may have moved on. Just start a new thread for your related topic.
  • Use the Private Message system for posts that are targeted at a specific person.


"PM Sent!" messages (or, how to use the Private Message system)

This forum has a private message feature that we want people to use for messages that are not of general interest to other members.

In short, if you are going to reply to a thread and that reply is targeted to a specific individual and not of interest to anybody else (either now or in the future) then send a private message instead.

Here are some obvious examples of when you should not reply to a thread and use the PM system instead:
  • "PM Sent!": Do not tell the rest of us that you sent a PM ... the forum software will tell the other person that they have a PM waiting.
  • "How much is shipping to ....": This is a very specific and directed question that is not of interest to anybody else.


Why do we have this policy? Sending a "PM Sent!" type message basically wastes everybody else's time by making them having to scroll past a post in a thread that looks to be updated, when the update is not meaningful. And the person you are sending the PM to will be notified by the forum software that they have a message waiting for them. Look up at the top near the right edge where it says 'Notifications' ... if you have a PM waiting, it will tell you there.

Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

Our discussions here generally fall under "fair use." Telling people how to pirate a software title is an example of something that is not allowable here.


Reporting problematic posts

If you see spam, a wildly off-topic post, or something abusive or illegal please report the thread by clicking on the "Report Post" icon. (It looks like an exclamation point in a triangle and it is available under every post.) This send a notification to all of the moderators, so somebody will see it and deal with it.

If you are unsure you may consider sending a private message to a moderator instead.


New user moderation

New users are directly moderated so that we can weed spammers out early. This means that for your first 10 posts you will have some delay before they are seen. We understand this can be disruptive to the flow of conversation and we try to keep up with our new user moderation duties to avoid undue inconvenience. Please do not make duplicate posts, extra posts to bump your post count, or ask the moderators to expedite this process; 10 moderated posts will go by quickly.

New users also have a smaller personal message inbox limit and are rate limited when sending PMs to other users.


Other suggestions
  • Use Google, books, or other definitive sources. There is a lot of information out there.
  • Don't make people guess at what you are trying to say; we are not mind readers. Be clear and concise.
  • Spelling and grammar are not rated, but they do make a post easier to read.
See more
See less

Using multiple controller cards, and learning about IRQs, DMAs, and I/Os

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Using multiple controller cards, and learning about IRQs, DMAs, and I/Os

    I'd like to try using multiple controller cards to control various drives simultaneously (hard drives, floppy drives, CD-ROM, magneto-optical drive, tape drive, whatever). I know that the following things exist for data flow, and they must be kept separate for everything to function.

    IRQ channels
    DMA addresses
    I/O addresses
    1. How many different IRQ channels are there? Sixteen, numbered 0 to 15.
    2. How many different DMA addresses are there?
    3. How many different I/O addresses are there?
    4. Are DMA addresses, RAM addresses, and I/O addresses referring to the same thing?
    5. Does every device I put into the computer need a unique IRQ channel?
    6. Does every device I put into the computer need a unique DMA address?
    7. IRQs seem to be generally controlled by jumpers on expansion boards. Are DMA addresses controlled by jumpers? If not, how are they controlled?


    If my mouse, for example, uses 3F8h, that is 3F8 hexadecimal = 1016 decimal = 1111111000 binary. Does that address then just refer to a specific RAM byte? Or is it a group of bytes? How many bytes are in the group?
    Sattinger’s Law: “It works better if you plug it in.” 🤯 Corollary: “It works even better if you plug it in correctly.” 🤯🤯
    "The simplest solution is the most likely solution." --My paraphrase of Occam's Razor
    "You can get [a computer] like yours at a garage sale for, like, fifteen dollars," --Strong Sad, sbemail #33

    #2
    Following answers are valid for the ISA bus. If otherwise, I'll mention it.

    [*]How many different IRQ channels are there? Sixteen, numbered 0 to 15.

    But you cannot use them all, certainly not on a 8088/8086 machine.

    [*]How many different DMA addresses are there?

    Eight, and again, not all usable. Please see: http://baltissen.org/newhtm/isabus.htm

    [*]How many different I/O addresses are there?

    $000 to $3FF. On PCI machines it can be up to $FFFF.

    [*]Are DMA addresses, RAM addresses, and I/O addresses referring to the same thing?

    Not at all. It aren't DMA addresses, it are single lines, see my page. The RAM and I/O addresses are different addresses. The 80x86 and Z80 support a separated I/O and memory range. The 6502, 6809 and 680x0 support memory mapped I/O.

    [*]Does every device I put into the computer need a unique IRQ channel?

    No. But the the IRQ routine for that channel must figure out which device generated the interrupt. This is something the Z80 and 6502 have to do all the time.

    [*]Does every device I put into the computer need a unique DMA address?

    Sorry, I don't know the answer for this question.

    [*]IRQs seem to be generally controlled by jumpers on expansion boards. Are DMA addresses controlled by jumpers? If not, how are they controlled?

    On older boards: yes. But by using extra ICs, a CPLD or FPGA, one can control what DMA or INQ to use by software.


    If my mouse, for example, uses 3F8h, that is 3F8 hexadecimal = 1016 decimal = 1111111000 binary. Does that address then just refer to a specific RAM byte? ]

    $3F8 to $3FF is reserved for COM1. This means your mouse is a serial mouse and not a bus mouse or a PS/2 mouse. And this is I/O, not RAM. Various parts of the I/O range is reserved for various I/O of the PC. $2F8 for COM2, $378 for LPT1, $278 for LPT2. But $3BC can be used by LPT1 as well and a LPT port on $378 becomes LPT2 then. Some I/O ranges are reserved for certain hardware. Some of those ranges you can use for your own purposes but be careful to use those other reserved ranges: the PC will search for this specific hardware but could be confused by yours.

    I hope this helps a bit.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

    Comment


      #3
      Originally posted by Ruud View Post
      No. But the the IRQ routine for that channel must figure out which device generated the interrupt. This is something the Z80 and 6502 have to do all the time.
      The 80x86 core itself only has mask-able and non-maskable interrupt pins, same as the Z80, it uses external interrupt controllers to cascade that out into the 8 or 15 individual IRQs (8 or 16 bit ISA respectively, not all available). They do the hardware needful to let the CPU figure out which IRQ line on the bus was pulled, IE, they essentially shove a byte onto the bus when the IRQ happens that tells the CPU which memory address to jump to to execute the handler.

      Sharing an IRQ between two different devices is technically possible, but it is *not* automatic on the ISA bus and few DOS drivers will support it. Essentially you get one "Jump here when you see this IRQ fired" signal from the hardware, and the software architecture lets *one* driver sit on that. To share an IRQ between two devices you'll need a driver that includes additional intelligence to determine which of those devices fired the interrupt pin; since there's no standard middleware for that under DOS you're essentially not going to be able to do it unless you're willing to write your own drivers for two devices you want to share.
      My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

      Comment


        #4
        I'm using a 386 ISA PC computer. It is a 27-inch tall tower, with 4 bays open to the front, and 2 3.5-inch bays internal only, where I have put hard drives. This is the case I want to use.

        The drives I expect I will use the most frequently I have already populated into the case:
        • 5.25-inch floppy (edge connector)
        • 3.5-inch floppy (edge connector)
        • internal Zip drive (IDE connector)
        • DVD drive (I will downgrade to a CD drive if I have to) (IDE connector either way)

        Of these, only the floppy drives are connected so far. I need to get hard drives working properly to install drivers for the others.

        The drives I can think of that I would want in case 2 are:
        • a magneto-optical drive (50-pin internal SCSI connector)
        • a tape drive (not bought yet)
        • a swappable hard drive bay for IDE drives (IDE connector)


        I've got enough controller cards to simultaneously reach all of these, so hopefully it will just be a matter of making sure the IRQs and DMAs and whatever else do not conflict.
        Sattinger’s Law: “It works better if you plug it in.” 🤯 Corollary: “It works even better if you plug it in correctly.” 🤯🤯
        "The simplest solution is the most likely solution." --My paraphrase of Occam's Razor
        "You can get [a computer] like yours at a garage sale for, like, fifteen dollars," --Strong Sad, sbemail #33

        Comment


          #5
          Other useful learning pages for IRQ, DMA, I/O, etc. These explain it pretty simply.

          https://www.escotal.com/IRQ.html

          https://www.helpwithpcs.com/upgradin...q-settings.htm

          https://www.pearsonitcertification.c...30360&seqNum=3
          Sattinger’s Law: “It works better if you plug it in.” 🤯 Corollary: “It works even better if you plug it in correctly.” 🤯🤯
          "The simplest solution is the most likely solution." --My paraphrase of Occam's Razor
          "You can get [a computer] like yours at a garage sale for, like, fifteen dollars," --Strong Sad, sbemail #33

          Comment


            #6
            I’d like to get back to this project, now that I’ve advanced a lot in knowing more and I've gotten many things to work since December 2020. I know my way around vintage computers not expertly, but way better than even a few months ago.

            Status updates:

            The tall tower 386 has ISA slots. I now have the following working:
            • Both floppy drives
            • Primary 425 MB. physical hard drive
            • Secondary 248 MB. physical hard drive
            • Sound Blaster 16 model CT1750
            • CF card adaptor board and several CF cards
            • Zip 100 parallel port drive
            • Serial mouse
            I also have the following available and have gotten them to work. They can’t all work at once, though (I need to install and properly configure a second controller card).
            • Conner tape drive for DC2120 tapes (34-pin)
            • CD-ROM drive (40-pin)
            (Regarding the magneto-optical drive I mentioned before and disks for it, it requires a 50-pin SCSI connection. I have the ISA SCSI controller card for this, too. But I will save that for another build.)

            I tried plugging the CD-ROM drive into the Panasonic 40-pin set on the Sound Blaster 16, and the Mitsumi 40-pin set, moving the jumper on the SB16 accordingly, but neither worked; MSCDEX.EXE was not able to find it. It looks like the CD-ROM drive can only work when it's connected to the controller card.

            I have a controller card that should work as the second controller card so I can connect the tape drive and CD-ROM drive.

            Motherboard: Micronics model 09-00021, 386DX, 25 MHz. (math coprocessor boosts it to 29 MHz.)

            Primary controller card: SIIG model CI_5000
            • Floppy channel connects to the two floppy drives
            • IDE hard drive channel 1 connects to the primary and secondary physical hard drives
            • IDE hard drive channel 2 connects to the CF card adaptor board. From what I’ve been able to tell, these CF card adaptor boards require themselves to be the only device on the channel.
            Proposed secondary controller card: SIIG model SC-JEE012
            • Floppy channel would connect to tape drive (and possibly a third floppy drive in the future)
            • IDE hard drive channel would connect to CD-ROM drive (and possibly a third hard drive in the future)
            So, the first questions are:
            1. What program can I use to peek at the DMA, I/O, and IRQ addresses?
              • I've got CheckIt 3.0, but I don't know if that will explicitly peek at the addresses and give a report on them.
            2. How do I change any of those values if I want to?
            3. How do I try to do this once I don't think I have any conflicts? Just plug all the hardware in and turn it on?
            Attached Files
            Sattinger’s Law: “It works better if you plug it in.” 🤯 Corollary: “It works even better if you plug it in correctly.” 🤯🤯
            "The simplest solution is the most likely solution." --My paraphrase of Occam's Razor
            "You can get [a computer] like yours at a garage sale for, like, fifteen dollars," --Strong Sad, sbemail #33

            Comment

            Working...
            X