Re: [PARPORT] base address?

From: Tim Waugh (
Date: Wed Apr 19 2000 - 04:41:34 EDT

  • Next message: zhu qun ying: "Re: [PARPORT] base address?"

    On Wed, Apr 19, 2000 at 09:14:58AM +0800, zhu qun ying wrote:

    > Now I have a more clear direction of what I want to ask. :).
    > For my implementation, whenever a read to the data line, the buffer chip have
    > to switch direction so that peripheral data can go through the buffer and
    > reach the processor.

    Yes, this is true for the PC ports as well.

    > And from my trace, my low level read function is called
    > without switching the data direction.

    Your low-level data-register read function is called before having the
    direction switched, and that is a bug in the caller. I can't see
    where that's happening though -- if you force an oops (*(int*)0=0)
    we'll be able to figure it out.

    It's okay for your low-level protocol read functions to be called
    without the caller having switched direction first though, since the
    protocol function should take care of it. Speaking of which, I think
    there's a bug in parport_ieee1284_read_byte (but I don't think you can
    be hitting that)..

    > For the low-level forward and reverse function, do I need to take
    > care of the signaling, or just switch the data line direction?

    Just the data line direction.

    > Here is the trace:
    > [root@Linux modules]$insmod parport_arm.o
    > parport0: cpp_daisy: aa5500ff(08)

    I think at this stage we are here:

    ->parport_daisy_init (first time)

    > parport0: assign_addrs: aa5500ff(08)


    > parport_arm_write_control() 0x0c
    > parport_arm_read_control()
    > parport_arm_write_control() 0x0c
    > parport_arm_read_control()
    > parport_arm_write_control() 0x06
    > parport_arm_read_control()
    > parport_arm_write_control() 0x0c
    > parport0: Peripheral not IEEE1284 compliant (0xC8)


    > parport_arm_read_data() <<-- read data line
    > parport_arm_data_reverse() <<-- switch direction inside arm_aread_data
    > parport_arm_data_forward() <<-- switch back "
    > parport_arm_read_control()

      ??? I don't see this in the code..

    > parport_arm_write_control() 0x08
    > parport_arm_write_control() 0x0c
    > parport0: cpp_mux: aa55f00f52ad51(38)
    > parport0: cpp_daisy: aa5500ff(38)
    > parport0: assign_addrs: aa5500ff(38)

    And this is the rest of parport_announce_port.


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