[9fans] Writing drivers in Plan 9 - Plan9

This is a discussion on [9fans] Writing drivers in Plan 9 - Plan9 ; Hello: I've been using Inferno and Plan 9 for almost a year. I certainly love Plan 9's ideas and concepts, and I'd be glad to finally move forward and leave Unix behind, but for now it is imposible for me, ...

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Thread: [9fans] Writing drivers in Plan 9

  1. [9fans] Writing drivers in Plan 9

    Hello:
    I've been using Inferno and Plan 9 for almost a year. I certainly love
    Plan 9's ideas and concepts, and I'd be glad to finally move forward
    and leave Unix behind, but for now it is imposible for me, since my
    work does not allow me this (I do data analysis for some physics
    experiment using Cern's ROOT).
    Anyway, I've always wanted to learn to write drivers and I did try it
    a few years ago, using NetBSD, but I could not find time to complete
    the task, so I leaved it unfinished. I want to start again, but this
    time using Plan 9. So, I want to ask you for some pointers about how
    doing this. Please, bear in mind, that I am a complete newbie when it
    comes about writing drivers.
    Saludos

    Hugo


  2. Re: [9fans] Writing drivers in Plan 9

    Given that you're already into Inferno as well as Plan 9, I
    think a really nice way to get into driver development is
    with emu drivers for Inferno. The basic structure is the
    same as for native OS drivers in either system: implement
    a small set of entry points (fooattach, fooread, &c),
    making use of the dev* defaults where appropriate. It's
    then a much smaller step to move into native hardware
    drivers for Plan 9 or Inferno. And when you do get to that
    point, take a look at Inferno's os/port/devXXX.c; it's a
    template for what you need to implement. In any case,
    the devtab (look for '^Dev') towards the end of any driver
    will tell you what you really need. It's a much nicer,
    constrained set for Inferno and Plan 9 than any unix.
    Anthony



  3. Re: [9fans] Writing drivers in Plan 9

    > Hello:
    > I've been using Inferno and Plan 9 for almost a year. I certainly love
    > Plan 9's ideas and concepts, and I'd be glad to finally move forward
    > and leave Unix behind, but for now it is imposible for me, since my
    > work does not allow me this (I do data analysis for some physics
    > experiment using Cern's ROOT).
    > Anyway, I've always wanted to learn to write drivers and I did try it
    > a few years ago, using NetBSD, but I could not find time to complete
    > the task, so I leaved it unfinished. I want to start again, but this
    > time using Plan 9. So, I want to ask you for some pointers about how
    > doing this. Please, bear in mind, that I am a complete newbie when it
    > comes about writing drivers.
    > Saludos


    a few thoughts from inexperience

    0. pick something you want to use.
    1. you must have a datasheet. reading other drivers for the same
    h/w can be very misleading before you're done.
    2. implement as few features as you need to get the hardware
    working for your purposes. it's likely the other stuff will never
    be needed,
    3. set up an whole plan 9 environment which can pxeboot
    your target machine. if you're like me, you'll be rebooting
    quite a bit.
    4, this is still true
    The most effective debugging tool is still careful thought,
    coupled with judiciously placed print statements.
    -Kernighan, 1978

    - erik



  4. Re: [9fans] Writing drivers in Plan 9

    > Given that you're already into Inferno as well as Plan 9, I
    > think a really nice way to get into driver development is
    > with emu drivers for Inferno. The basic structure is the
    > same as for native OS drivers in either system: implement
    > a small set of entry points (fooattach, fooread, &c),
    > making use of the dev* defaults where appropriate. It's
    > then a much smaller step to move into native hardware
    > drivers for Plan 9 or Inferno. And when you do get to that
    > point, take a look at Inferno's os/port/devXXX.c; it's a
    > template for what you need to implement. In any case,
    > the devtab (look for '^Dev') towards the end of any driver
    > will tell you what you really need. It's a much nicer,
    > constrained set for Inferno and Plan 9 than any unix.
    > Anthony


    i think this confuses implementing a Dev interface with writing
    a device driver. for many devices, the Dev interface is already
    taken care of. for example, serial, ethernet, disk devices using
    sd implement an interface to devsd, ethernet.

    i don't buy the thesis that talking to hardware is always hard.
    talking to some hardware can be hard. for exampe, the aoe driver
    doesn't talk to hardware, it talks to the ethernet drivers. yet it's
    the largest driver i've written, largely because it implements its own
    dev interface.

    i think it's a mistake to think hardware == hard, software interfaces
    == easy.

    - erik



  5. Re: [9fans] Writing drivers in Plan 9

    > i think this confuses implementing a Dev interface with writing
    > a device driver. for many devices, the Dev interface is already
    > taken care of. for example, serial, ethernet, disk devices using
    > sd implement an interface to devsd, ethernet.


    i think the Dev interface is still the right place to start, in terms of
    understanding things.

    for the benifit of the original question, the Dev interface (that
    common set of entry points i was talking about) is the common
    kernel interface that all device drivers have to go through at some
    point. i think part of erik's point (which is correct) is that many of
    the things people are commonly writing drivers for - disk
    controllers, ethernet cards, and vga cards being probably the most
    common examples - already have that interface covered, and
    there's a separate interface that the hardware-specific part needs
    to talk to.

    > i don't buy the thesis that talking to hardware is always hard.
    > talking to some hardware can be hard. for exampe, the aoe driver
    > doesn't talk to hardware, it talks to the ethernet drivers. yet it's
    > the largest driver i've written, largely because it implements its own
    > dev interface.


    but working with Dev doesn't need to be so complex; it depends, at a
    minimum, on what the job you're trying to do is. dup and env
    both implement at least most of their own Dev interface (as opposed
    to relying on many of the default stubs), but are reasonably short and
    easy to understand. devaoe's hardly a fair comparison; it's not only
    the largest driver you've written, it's the largest dev*.c in the system.

    > i think it's a mistake to think hardware == hard, software interfaces
    > == easy.


    agreed. but it's also a mistake, at least in the context of Plan 9, to
    assume that device drivers inherently involve hardware. about a third
    of the things in section three of the manual don't.

    anthony



  6. Re: [9fans] Writing drivers in Plan 9

    Thanks for your feedback.
    Now, I think I am going to start by trying to understand a little
    about the Dev interface you talk about, and then continue to write a
    real driver for a gamepad that I have.
    Is there any documentation that describes this Dev interface?
    This is a usb gamepad, so probably I have to deal with a Dev interface
    related to the usb ports, am I right?

    Hugo

    2008/4/15, a@9srv.net :
    > > i think this confuses implementing a Dev interface with writing
    > > a device driver. for many devices, the Dev interface is already
    > > taken care of. for example, serial, ethernet, disk devices using
    > > sd implement an interface to devsd, ethernet.

    >
    >
    > i think the Dev interface is still the right place to start, in terms of
    > understanding things.
    >
    > for the benifit of the original question, the Dev interface (that
    > common set of entry points i was talking about) is the common
    > kernel interface that all device drivers have to go through at some
    > point. i think part of erik's point (which is correct) is that many of
    > the things people are commonly writing drivers for - disk
    > controllers, ethernet cards, and vga cards being probably the most
    > common examples - already have that interface covered, and
    > there's a separate interface that the hardware-specific part needs
    > to talk to.
    >
    >
    > > i don't buy the thesis that talking to hardware is always hard.
    > > talking to some hardware can be hard. for exampe, the aoe driver
    > > doesn't talk to hardware, it talks to the ethernet drivers. yet it's
    > > the largest driver i've written, largely because it implements its own
    > > dev interface.

    >
    >
    > but working with Dev doesn't need to be so complex; it depends, at a
    > minimum, on what the job you're trying to do is. dup and env
    > both implement at least most of their own Dev interface (as opposed
    > to relying on many of the default stubs), but are reasonably short and
    > easy to understand. devaoe's hardly a fair comparison; it's not only
    > the largest driver you've written, it's the largest dev*.c in the system.
    >
    >
    > > i think it's a mistake to think hardware == hard, software interfaces
    > > == easy.

    >
    >
    > agreed. but it's also a mistake, at least in the context of Plan 9, to
    > assume that device drivers inherently involve hardware. about a third
    > of the things in section three of the manual don't.
    >
    > anthony
    >
    >
    >



  7. Re: [9fans] Writing drivers in Plan 9

    > Thanks for your feedback.
    > Now, I think I am going to start by trying to understand a little
    > about the Dev interface you talk about, and then continue to write a
    > real driver for a gamepad that I have.
    > Is there any documentation that describes this Dev interface?
    > This is a usb gamepad, so probably I have to deal with a Dev interface
    > related to the usb ports, am I right?
    >
    > Hugo


    probablly not. the usb stuff is all accessable from userland. usbd
    runs in user space as do all the clients of usb -- usb/disk usb/mouse, etc.

    - erik



  8. Re: [9fans] Writing drivers in Plan 9

    > probablly not. the usb stuff is all accessable from userland. usbd
    > runs in user space as do all the clients of usb -- usb/disk usb/mouse, etc.


    So, this means that I never have to deal with usb interfaces?
    Can you point me some documentation about this?

    Hugo


  9. Re: [9fans] Writing drivers in Plan 9

    > So, this means that I never have to deal with usb interfaces?
    > Can you point me some documentation about this?
    >
    > Hugo


    it should be in the manul pages. try
    ; lookman usb

    - erik



  10. Re: [9fans] Writing drivers in Plan 9

    > it should be in the manul pages. try
    > ; lookman usb


    Great! thanks

    Hugo


  11. Re: [9fans] Writing drivers in Plan 9

    On Tue, Apr 15, 2008 at 4:40 AM, hugo rivera wrote:
    > Anyway, I've always wanted to learn to write drivers and I did try it
    > a few years ago, using NetBSD, but I could not find time to complete
    > the task, so I leaved it unfinished. I want to start again, but this
    > time using Plan 9. So, I want to ask you for some pointers about how
    > doing this. Please, bear in mind, that I am a complete newbie when it
    > comes about writing drivers.


    Did you do it? How did it go?

    --
    Tom Lieber
    http://AllTom.com/


  12. Re: [9fans] Writing drivers in Plan 9

    Sadly I cannot find time for Plan 9 for now. I am just too busy with
    my job in the university and preparing me for some tests in October.
    Hopefully I can start this thing in November.

    2008/9/3 Tom Lieber :
    > On Tue, Apr 15, 2008 at 4:40 AM, hugo rivera wrote:
    >> Anyway, I've always wanted to learn to write drivers and I did try it
    >> a few years ago, using NetBSD, but I could not find time to complete
    >> the task, so I leaved it unfinished. I want to start again, but this
    >> time using Plan 9. So, I want to ask you for some pointers about how
    >> doing this. Please, bear in mind, that I am a complete newbie when it
    >> comes about writing drivers.

    >
    > Did you do it? How did it go?
    >
    > --
    > Tom Lieber
    > http://AllTom.com/
    >
    >




    --
    Saludos

    Hugo


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